"Incus" means "anvil" in Latin. Several sources  attribute the discovery of the incus to the anatomist and philosopher  Alessandro Achillini . [ 4 ] [ 5 ]  The first brief written description of the  incus  was by  Berengario da Carpi  in his  Commentaria super anatomia Mundini  (1521). [ 6 ]   Andreas Vesalius , in his  De humani corporis fabrica , [ 7 ]  was the first to compare the second element of the ossicles to an anvil, thereby giving it the name  incus . [ 8 ]  The final part of the long limb was once described as a "fourth ossicle" by  Pieter Paaw  in 1615. [ 9 ]


The  inferior nasal concha  ( inferior turbinated bone  or  inferior turbinal/turbinate ) is one of the three paired  nasal conchae  in the  nose . It extends horizontally along the lateral wall of the  nasal cavity  and consists of a  lamina  of spongy  bone , curled upon itself like a scroll, ( turbinate  meaning inverted cone). [ 1 ]   The inferior nasal conchae are considered a pair of facial bones. As the air passes through the turbinates, the air is churned against these mucosa-lined bones in order to receive warmth, moisture and cleansing. Superior to inferior nasal concha are the  middle nasal concha  and  superior nasal concha  which both arise from the  ethmoid bone , of the cranial portion of the skull. [ 2 ]  Hence, these two are considered as a part of the cranial bones.


It has two surfaces, two borders, and two extremities.


The  medial surface  is  convex , perforated by numerous apertures, and traversed by longitudinal grooves for the lodgement of vessels.


The  lateral surface  is  concave , and forms part of the  inferior meatus .


Its  upper border  is thin, irregular, and connected to various bones along the lateral wall of the nasal cavity.


It may be divided into three portions: of these,


The  inferior border  is free, thick, and cellular in structure, more especially in the middle of the bone.


Both extremities are more or less pointed, the posterior being the more tapering.


The inferior nasal concha is ossified from a single center, which appears about the fifth month of fetal life in the lateral wall of the  cartilaginous nasal capsule . [ citation needed ]


The entire inferior concha may be absent in some people. This is a consequence of embryologic  agenesis  and is a normal anatomic variant. [ 3 ]


Large, swollen inferior turbinates may lead to blockage of nasal breathing.  Allergies , exposure to environmental  irritants , or a persistent  inflammation  within the sinuses can lead to turbinate swelling. Deformity of the  nasal septum  can also result in enlarged turbinates.


Treatment of the underlying allergy or irritant may reduce turbinate swelling. In cases that do not resolve, or for treatment of  deviated septum , turbinate surgery may be required.


Inferior  turbinate reduction  is a surgery to reduce the size of the inferior turbinates. There are different techniques, including bipolar  radiofrequency ablation  (also known as  somnoplasty ),  electrocautery , and use of cold steel instruments (eg, microdebrider).  Inferior turbinectomy  is a surgery to remove the  inferior turbinates .


In the case of  turbinate reduction , only small amounts of turbinate tissue are removed because the turbinates are essential for respiration.  Turbinectomy  is usually reserved for patients who have persistent symptoms despite previous  turbinate reduction  surgery. Risks of reduction of the inferior or middle turbinates include  empty nose syndrome .


This article incorporates text in the  public domain  from  page 169  of the 20th edition of   Gray's Anatomy   (1918)


The  infratemporal space  (also termed the  infra-temporal space  or the  infra-temporal portion of the deep temporal space ) [ 1 ]  is a  fascial space of the head and neck  (sometimes also termed  fascial  spaces or tissue spaces). It is a  potential space  in the side of the head, and is paired on either side. It is located posterior to the  maxilla , between the  lateral pterygoid plate  of the  sphenoid bone  medially and by the  base of skull  superiorly. [ 2 ]  The term is derived from  infra-  meaning below and  temporal  which refers to the  temporalis muscle .


The infratemporal space is the inferior portion of the  deep temporal space , which is one of the four  compartments  of the  masticator space , along with the  pterygomandibular space , the  submasseteric space  and the  superficial temporal space . [ 2 ]  The deep temporal space is separated from the pterygomandibular space by the  lateral pterygoid muscle  inferiorly and from the superficial temporal space by the temporalis muscle laterally. The deep temporal space and the superficial temporal space together make up the temporal spaces. [ 3 ]


The boundaries of the infratemporal space are: [ 4 ]


The communications of the infratemporal space are: [ 4 ]


The contents of the infratemporal space are: [ 2 ]


Infections of the infratemporal space are rare. They may be significant however, as it is possible for infection to spread via emissary veins from the pterygoid plexus to the cavernous sinus, which may result in  cavernous sinus thrombosis , a rare but life-threatening condition. [ 2 ]
The signs and symptoms of an infratemporal space infection are swelling of the face in the region of the  sigmoid notch , swelling of the mouth in the region of the maxillary tuberosity and marked  trismus  (difficulty opening the mouth), since some of the  muscles of mastication  are restricted by the swelling. [ 4 ]  Treatment of an abscess of this space is usually by surgical  incision and drainage , with the incision being placed on the face (a small horizontal incision posterior to the junction of the temporal and frontal process of the  zygomatic bone . or both on the face and inside the mouth. [ 2 ]


The spread of  odontogenic infections  may sometimes involve the infratemporal space. The most likely causative tooth is the maxillary third molar (upper  wisdom tooth ).


The  inner ear  ( internal ear ,  auris interna ) is the innermost part of the vertebrate  ear . In  vertebrates , the inner ear is mainly responsible for sound detection and balance. [ 1 ]  In  mammals , it consists of the  bony labyrinth , a hollow cavity in the  temporal bone  of the skull with a system of passages comprising two main functional parts: [ 2 ]


The inner ear is found in all vertebrates, with substantial variations in form and function. The inner ear is innervated by the eighth  cranial nerve  in all vertebrates.


The labyrinth can be divided by layer or by region.


The  bony labyrinth , or osseous labyrinth, is the network of passages with bony walls lined with  periosteum . The three major parts of the bony labyrinth are the  vestibule of the ear , the  semicircular canals , and the  cochlea . The  membranous labyrinth  runs inside of the bony labyrinth, and creates three parallel fluid filled spaces. The two outer are filled with  perilymph  and the inner with endolymph. [ 3 ]


In the  middle ear , the energy of  pressure waves  is translated into mechanical vibrations by the three auditory ossicles. Pressure waves move the tympanic membrane which in turns moves the malleus, the first bone of the middle ear. The malleus articulates to incus which connects to the stapes. The footplate of the stapes connects to the oval window, the beginning of the inner ear. When the stapes presses on the oval window, it causes the perilymph, the liquid of the inner ear to move. The middle ear thus serves to convert the energy from sound pressure waves to a force upon the perilymph of the inner ear. The oval window has only approximately 1/18 the area of the tympanic membrane and thus produces a higher  pressure . The cochlea propagates these mechanical signals as waves in the fluid and membranes and then converts them to nerve impulses which are transmitted to the brain. [ 4 ]


The vestibular system is the region of the inner ear where the semicircular canals converge, close to the cochlea. The vestibular system works with the visual system to keep objects in view when the head is moved. Joint and muscle receptors are also important in maintaining balance. The brain receives, interprets, and processes the information from all these systems to create the sensation of balance.


The vestibular system of the inner ear is responsible for the sensations of balance and motion.  It uses the same kinds of fluids and detection cells ( hair cells ) as the cochlea uses, and sends information to the brain about the attitude, rotation, and linear motion of the head.  The type of motion or attitude detected by a hair cell depends on its associated mechanical structures, such as the curved tube of a semicircular canal or the calcium carbonate crystals ( otolith ) of the  saccule  and  utricle .


The human inner ear develops during week 4 of  embryonic development  from the  auditory placode , a thickening of the  ectoderm  which gives rise to the  bipolar neurons  of the  cochlear  and  vestibular ganglions . [ 5 ]  As the auditory placode invaginates towards the embryonic  mesoderm , it forms the auditory vesicle or  otocyst .


The  auditory vesicle  will give rise to the utricular and saccular components of the  membranous labyrinth . They contain the sensory hair cells and  otoliths  of the  macula of utricle  and  of the saccule , respectively, which respond to  linear acceleration  and the force of  gravity . The utricular division of the auditory vesicle also responds to  angular acceleration , as well as the  endolymphatic sac  and  duct  that connect the saccule and utricle.


Beginning in the fifth week of development, the auditory vesicle also gives rise to the  cochlear duct , which contains the spiral  organ of Corti  and the  endolymph  that accumulates in the membranous labyrinth. [ 6 ]  The  vestibular wall  will separate the cochlear duct from the perilymphatic  scala vestibuli , a cavity inside the cochlea. The  basilar membrane  separates the cochlear duct from the  scala tympani , a cavity within the cochlear labyrinth. The lateral wall of the cochlear duct is formed by the  spiral ligament  and the  stria vascularis , which produces the  endolymph . The  hair cells  develop from the lateral and medial ridges of the cochlear duct, which together with the  tectorial membrane  make up the organ of Corti. [ 6 ]


Rosenthal's canal or the spiral canal of the cochlea is a section of the bony labyrinth of the inner ear that is approximately 30 mm long and makes 2¾ turns about the  modiolus , the central axis of the cochlea that contains the  spiral ganglion .


Specialized inner ear cell include: hair cells, pillar cells, Boettcher's cells, Claudius' cells, spiral ganglion neurons, and Deiters' cells (phalangeal cells).


The hair cells are the primary auditory receptor cells and they are also known as auditory sensory cells, acoustic hair cells, auditory cells or cells of Corti. The  organ of Corti  is lined with a single row of inner hair cells and three rows of outer hair cells. The hair cells have a hair bundle at the apical surface of the cell. The hair bundle consists of an array of actin-based stereocilia. Each stereocilium inserts as a rootlet into a dense filamentous actin mesh known as the cuticular plate. Disruption of these bundles results in hearing impairments and balance defects.


Inner and outer pillar cells in the organ of Corti support hair cells. Outer pillar cells are unique because they are free standing cells which only contact adjacent cells at the bases and apices. Both types of pillar cell have thousands of cross linked  microtubules  and  actin  filaments in parallel orientation. They provide mechanical coupling between the  basement membrane  and the  mechanoreceptors  on the hair cells.


Boettcher's cells  are found in the organ of Corti where they are present only in the lower turn of the cochlea. They lie on the basilar membrane beneath Claudius' cells and are organized in rows, the number of which varies between species. The cells interdigitate with each other, and project  microvilli  into the intercellular space. They are supporting cells for the auditory hair cells in the organ of Corti. They are named after German pathologist  Arthur Böttcher  (1831–1889).


Claudius' cells  are found in the organ of Corti located above rows of Boettcher's cells. Like Boettcher's cells, they are considered supporting cells for the auditory hair cells in the organ of Corti. They contain a variety of  aquaporin  water channels and appear to be involved in ion transport. They also play a role in sealing off endolymphatic spaces. They are named after the German anatomist  Friedrich Matthias Claudius  (1822–1869).


Deiters' cells  (phalangeal cells) are a type of  neuroglial  cell found in the organ of Corti and organised in one row of inner phalangeal cells and three rows of outer phalangeal cells. They are the supporting cells of the hair cell area within the cochlea. They are named after the German pathologist Otto Deiters (1834–1863) who described them.


Hensen's cells  are high columnar cells that are directly adjacent to the third row of Deiters' cells.


Hensen's stripe  is the section of the tectorial membrane above the inner hair cell.


Nuel's spaces  refer to the fluid-filled spaces between the outer pillar cells and adjacent hair cells and also the spaces between the outer hair cells.


Hardesty's membrane  is the layer of the tectoria closest to the reticular lamina and overlying the outer hair cell region.


Reissner's membrane  is composed of two cell layers and separates the scala media from the scala vestibuli.


Huschke's teeth  are the tooth-shaped ridges on the spiral limbus that are in contact with the tectoria and separated by interdental cells.


The bony labyrinth receives its blood supply from three arteries:
1 – Anterior tympanic branch (from maxillary artery).
2 – Petrosal branch (from middle meningeal artery).
3 – Stylomastoid branch (from posterior auricular artery).
The  membranous labyrinth  is supplied by the  labyrinthine artery .
Venous drainage of the inner ear is through the labyrinthine vein, which empties into the  sigmoid sinus  or  inferior petrosal sinus .


Neurons within the ear respond to simple tones, and the brain serves to process other increasingly complex sounds. An average adult is typically able to detect sounds ranging between 20 and 20,000 Hz. The ability to detect higher pitch sounds decreases in older humans.


The human ear has evolved with two basic tools to encode sound waves; each is separate in detecting high and low-frequency sounds.  Georg von Békésy  (1899–1972) employed the use of a microscope in order to examine the basilar membrane located within the inner-ear of cadavers. He found that movement of the basilar membrane resembles that of a traveling wave; the shape of which varies based on the frequency of the pitch. In low-frequency sounds, the tip (apex) of the membrane moves the most, while in high-frequency sounds, the base of the membrane moves most. [ 7 ]


Interference with or infection of the labyrinth can result in a syndrome of ailments called  labyrinthitis .  The symptoms of labyrinthitis include temporary nausea, disorientation, vertigo, and dizziness. Labyrinthitis can be caused by viral infections, bacterial infections, or physical blockage of the inner ear. [ 8 ] [ 9 ]


Another condition has come to be known as autoimmune inner ear disease (AIED). It is characterized by idiopathic, rapidly progressive, bilateral sensorineural hearing loss. It is a fairly rare disorder while at the same time, a lack of proper diagnostic testing has meant that its precise incidence cannot be determined. [ 10 ]


Birds have an auditory system similar to that of mammals, including a cochlea. Reptiles, amphibians, and fish do not have cochleas but hear with simpler auditory organs or vestibular organs, which generally detect lower-frequency sounds than the cochlea.  The cochlea of birds is also similar to that of crocodiles, consisting of a short, slightly curved bony tube within which lies the basilar membrane with its sensory structures. [ 11 ]


In  reptiles , sound is transmitted to the inner ear by the  stapes  (stirrup) bone of the middle ear. This is pressed against the  oval window , a membrane-covered opening on the surface of the vestibule. From here, sound waves are conducted through a short  perilymphatic duct  to a second opening, the  round window , which equalizes pressure, allowing the incompressible fluid to move freely. Running parallel with the perilymphatic duct is a separate blind-ending duct, the  lagena , filled with  endolymph . The lagena is separated from the perilymphatic duct by a  basilar membrane , and contains the sensory hair cells that finally translate the vibrations in the fluid into nerve signals. It is attached at one end to the saccule. [ 12 ]


In most reptiles the perilymphatic duct and lagena are relatively short, and the sensory cells are confined to a small  basilar papilla  lying between them. However, in  mammals ,  birds , and  crocodilians , these structures become much larger and somewhat more complicated. In birds, crocodilians, and  monotremes , the ducts are simply extended, together forming an elongated, more or less straight, tube. The endolymphatic duct is wrapped in a simple loop around the lagena, with the basilar membrane lying along one side. The first half of the duct is now referred to as the  scala vestibuli , while the second half, which includes the basilar membrane, is called the  scala tympani . As a result of this increase in length, the basilar membrane and papilla are both extended, with the latter developing into the  organ of Corti , while the lagena is now called the  cochlear duct . All of these structures together constitute the cochlea. [ 12 ]


In  therian  mammals, the lagena is extended still further, becoming a coiled structure (cochlea) in order to accommodate its length within the head. The organ of Corti also has a more complex structure in mammals than it does in other  amniotes . [ 12 ]


The arrangement of the inner ear in living  amphibians  is, in most respects, similar to that of reptiles. However, they often lack a basilar papilla, having instead an entirely separate set of sensory cells at the upper edge of the saccule, referred to as the  papilla amphibiorum , which appear to have the same function. [ 12 ]


Although many fish are capable of hearing, the lagena is, at best, a short diverticulum of the saccule, and appears to have no role in sensation of sound. Various clusters of hair cells within the inner ear may instead be responsible; for example,  bony fish  contain a sensory cluster called the  macula neglecta  in the utricle that may have this function. Although fish have neither an outer nor a middle ear, sound may still be transmitted to the inner ear through the bones of the skull, or by the  swim bladder , parts of which often lie close by in the body. [ 12 ]


By comparison with the  cochlear  system, the  vestibular system  varies relatively little between the various groups of  jawed vertebrates . The central part of the system consists of two chambers, the saccule and utricle, each of which includes one or two small clusters of sensory hair cells. All jawed vertebrates also possess three semicircular canals arising from the utricle, each with an  ampulla  containing sensory cells at one end. [ 12 ]


An  endolymphatic duct  runs from the saccule up through the head and ending close to the brain. In  cartilaginous fish , this duct actually opens onto the top of the head, and in some  teleosts , it is simply blind-ending. In all other species, however, it ends in an  endolymphatic sac . In many reptiles, fish, and amphibians this sac may reach considerable size. In amphibians the sacs from either side may fuse into a single structure, which often extends down the length of the body, parallel with the  spinal canal . [ 12 ]


The primitive  lampreys  and  hagfish , however, have a simpler system. The inner ear in these species consists of a single vestibular chamber, although in lampreys, this is associated with a series of sacs lined by  cilia . Lampreys have only two semicircular canals, with the horizontal canal being absent, while hagfish have only a single, vertical, canal. [ 12 ]


The inner ear is primarily responsible for balance, equilibrium and orientation in three-dimensional space. The inner ear can detect both static and dynamic equilibrium. Three  semicircular ducts  and two chambers, which contain the  saccule  and  utricle , enable the body to detect any deviation from equilibrium. The macula sacculi detects vertical acceleration while the  macula utriculi  is responsible for horizontal acceleration. These microscopic structures possess stereocilia and one kinocilium which are located within the gelatinous otolithic membrane. The membrane is further weighted with otoliths. Movement of the stereocilia and kinocilium enable the hair cells of the saccula and utricle to detect motion. The semicircular ducts are responsible for detecting rotational movement. [ 13 ]


The  internal auditory meatus  (also  meatus acusticus internus ,  internal acoustic meatus ,  internal auditory canal , or  internal acoustic canal ) is a canal within the  petrous part of the temporal bone  of the  skull  between the  posterior cranial fossa  and the  inner ear .


The opening to the meatus is called the  porus acusticus internus  or  internal acoustic opening . It is located inside the  posterior cranial fossa  of the skull, near the center of the posterior surface of the petrous part of the temporal bone.  The size varies considerably. Its outer margins are smooth and rounded.


The canal which comprises the internal auditory meatus is short (about 1 cm) and runs laterally into the bone.


The lateral (outer) aspect of the canal is known as the  fundus . [ 1 ]  The fundus is subdivided by two thin crests of bone to form three separate canals, through which course the  facial  and  vestibulocochlear nerve  branches. [ citation needed ]  The falciform crest first divides the meatus into superior and inferior sections; a vertical crest (Bill's bar, named by  William F. House ) then divides the upper passage into anterior and posterior sections. [ 2 ]  Although there are three osseous canals, the fundus is conceptually divided more commonly into four quadrant areas according to the four major nerve branches of the inner ear:


The cochlear and vestibular branches of cranial nerve VIII separate according to this schema and terminate in the inner ear. The facial nerve continues traveling through the  facial canal , eventually exiting the skull at the  stylomastoid foramen . A common mnemonic to remember the anterior quadrants of the inner ear is: "seven up, coke down" (seventh nerve superior, cochlear nerve inferior).


The internal auditory meatus provides a passage through which the  vestibulocochlear nerve  (CN VIII), the  facial nerve  (CN VII), and the  labyrinthine artery  (an internal auditory branch of the  anterior inferior cerebellar artery  in 85% of people) can pass from inside the skull to structures of the inner ear and face. It also contains the  vestibular ganglion .


The  internal carotid artery  is an  artery  in the  neck  which supplies the  anterior  and  middle   cerebral circulation . [ 1 ]


In human anatomy, the internal and  external  carotid arise from the  common carotid artery , where it bifurcates at  cervical vertebrae  C3 or C4. The internal carotid artery supplies the  brain , including the eyes, [ 2 ]  while the external carotid nourishes other portions of the head, such as the  face ,  scalp ,  skull , and  meninges .


Terminologia Anatomica  in 1998 subdivided the artery into four parts: "cervical", "petrous", "cavernous", and "cerebral". [ 3 ] [ 4 ]


In clinical settings, however, usually the classification system of the internal carotid artery follows the 1996 recommendations by Bouthillier, [ 5 ]  describing seven anatomical segments of the internal carotid artery, each with a corresponding alphanumeric identifier: C1 cervical; C2 petrous; C3 lacerum; C4 cavernous; C5 clinoid; C6 ophthalmic; and C7 communicating. The Bouthillier nomenclature remains in widespread use by neurosurgeons, neuroradiologists and neurologists.


The segments are subdivided based on anatomical and microsurgical landmarks and surrounding anatomy, more than  angiographic  appearance of the artery. An alternative  embryologic  classification system proposed by  Pierre Lasjaunias [ 6 ]  and colleagues is invaluable when it comes to explanation of many internal carotid artery variants. An older clinical classification, based on pioneering work by Fischer, [ 7 ]  is mainly of historical significance.


The segments of the internal carotid artery are as follows:


The internal carotid artery is a terminal branch of the  common carotid artery ; it arises around the level of the fourth cervical  vertebra  when the common carotid bifurcates into this artery and its more superficial counterpart, the  external carotid artery .


The  cervical segment , or C1, or  cervical part of the internal carotid , extends from the carotid bifurcation until it enters the  carotid canal  in the skull anterior to the  jugular foramen .


At its origin, the internal carotid artery is somewhat dilated. This part of the artery is known as the  carotid sinus  or the carotid bulb. The ascending portion of the cervical segment occurs distal to the bulb when the vessel walls are again parallel.


The internal carotid runs vertically upward in the  carotid sheath  and enters the  skull  through the  carotid canal . During this part of its course, it lies in front of the  transverse processes  of the upper three cervical vertebrae.


It is relatively superficial at its start, where it is contained in the  carotid triangle  of the neck, and lies behind and medial to the external carotid, overlapped by the  sternocleidomastoid  muscle, and covered by the deep fascia, the  platysma , and integument: it then passes beneath the  parotid gland , being crossed by the  hypoglossal nerve , the  digastric muscle  and the  stylohyoid muscle , the  occipital artery  and the  posterior auricular artery . Higher up, it is separated from the external carotid by the  styloglossus  and  stylopharyngeus  muscles, the tip of the  styloid process  and the  stylohyoid ligament , the  glossopharyngeal nerve  and the pharyngeal branch of the  vagus nerve . It is in relation, behind, with the  longus capitis , the  superior cervical ganglion  of the  sympathetic trunk , and the  superior laryngeal nerve ; laterally, with the  internal jugular vein  and  vagus nerve , the nerve lying on a plane posterior to the artery; medially, with the  pharynx ,  superior laryngeal nerve , and  ascending pharyngeal artery . At the base of the skull the  glossopharyngeal , vagus,  accessory , and  hypoglossal  nerves lie between the artery and the  internal jugular vein .


Unlike the  external carotid artery , the internal carotid normally has no branches in the  neck .


The  petrous segment , or C2, of the internal carotid, is that which is inside the petrous part of the  temporal bone . This segment extends until the  foramen lacerum .


The petrous portion classically has three sections:


When the internal carotid artery enters the canal in the  petrous portion of the temporal bone , it first ascends a short distance and then curves anteriorly and medially. The artery lies at first in front of the  cochlea  and  tympanic cavity ; from the latter cavity it is separated by a thin, bony lamella, which is cribriform in the young subject, and often partly absorbed in old age. Farther forward, it is separated from the  trigeminal ganglion  by a thin plate of bone, which forms the floor of the fossa for the ganglion and the roof of the horizontal portion of the canal. Frequently this bony plate is more or less deficient, and then the ganglion is separated from the artery by fibrous membrane. The artery is separated from the bony wall of the  carotid canal  by a prolongation of  dura mater  and is surrounded by a number of small veins and by filaments of the  carotid plexus , derived from the ascending branch of the  superior cervical ganglion  of the sympathetic trunk.


The named branches of the petrous segment of the internal carotid artery are:


The  lacerum segment , or C3, is a short segment that begins above the  foramen lacerum  and ends at the  petrolingual ligament , a reflection of  periosteum  between the lingula and petrous apex (or petrosal process) of the  sphenoid bone . The lacerum portion is still considered "extradural" since it is surrounded by periosteum and fibrocartilage along its course. It is erroneously stated in several anatomy textbooks that the internal carotid artery passes through the foramen lacerum. This at best has only ever been a partial truth in that it passes through the superior part of the foramen on its way to the cavernous sinus. As such it does not traverse the skull through it. The inferior part of the foramen is actually filled with fibrocartilage. The broad consensus is that the internal carotid artery should not be described as travelling through the foramen lacerum. [ 8 ]


The  cavernous segment , or C4, of the internal carotid artery begins at the petrolingual ligament and extends to the proximal dural ring, which is formed by the medial and inferior periosteum of the anterior clinoid process. The cavernous segment is surrounded by the  cavernous sinus .


In this part of its course, the artery is situated between the layers of the  dura mater  forming the  cavernous sinus , but covered by the lining membrane of the sinus. It at first ascends toward the  posterior clinoid process , then passes forward by the side of the  body of the sphenoid bone , again curves upward on the medial side of the  anterior clinoid process , and perforates the dura mater forming the roof of the sinus. The curve in the cavernous segment is called the  carotid siphon . This portion of the artery is surrounded by filaments of the sympathetic trunk, and on its lateral side is the  abducent nerve , or cranial nerve VI.


The named branches of the cavernous segment are:


The cavernous segment also gives rise to small capsular arteries that supply the wall of the cavernous sinus.


The  clinoid segment , or C5, is another short segment of the internal carotid that begins after the artery exits the  cavernous sinus  at the proximal dural ring and extends distally to the distal dural ring, after which the carotid artery is considered "intra-dural" and has entered the  subarachnoid space .


The clinoid segment normally has no named branches, though the  ophthalmic artery  may arise from the clinoid segment.


The  ophthalmic segment , or C6, extends from the distal dural ring, which is continuous with the falx cerebri, to the origin of the  posterior communicating artery . The ophthalmic segment courses roughly horizontally, parallel to the  optic nerve , which runs superomedially to the carotid at this point.


The named branches of the ophthalmic segment are:


The  communicating segment , or terminal segment, or C7, of the internal carotid artery passes between the optic and oculomotor nerves to the anterior perforated substance at the medial extremity of the lateral cerebral fissure. Angiographically, this segment extends from the origin of the  posterior communicating artery  to the bifurcation of the internal carotid artery.


The named branches of the communicating segment are:


The internal carotid then divides to form the  anterior cerebral artery  and  middle cerebral artery . The  circle of Willis  provides a  collateral pathway  for blood supply to the brain.


The following are the branches of the internal carotid artery, listed by segment: [ 9 ]


The  sympathetic trunk  forms a plexus of nerves around the artery known as the  carotid plexus . The  internal carotid nerve  arises from the  superior cervical ganglion , and forms this plexus, which follows the internal carotid into the skull.


The state and health of internal carotid arteries is usually evaluated using  doppler ultrasound ,  CT angiogram  or  phase contrast magnetic resonance imaging  (PC-MRI).


Typically internal carotid artery blood flow velocities are measured in peak systolic velocity (PSV) and end diastolic velocity (EDV) and according to Society of Radiologists in Ultrasound in healthy subjects without stenosis must be below 125 cm/sec at PSV and below 40 cm/sec at EDV. [ 10 ]


One study found that for  normative  males in the 20-39 age group, PSV averaged 82 cm/sec and EDV 34 cm/sec. In the male 80+ age group, PSV averaged 76 cm/sec and EDV 18 cm/sec. [ 11 ]


This article incorporates text in the  public domain  from  page 566  of the 20th edition of   Gray's Anatomy   (1918)


The  internal jugular vein  is a paired  jugular vein  that collects blood from the  brain  and the superficial parts of the  face  and  neck . This vein runs in the  carotid sheath  with the  common carotid artery  and  vagus nerve .


It begins in the posterior compartment of the  jugular foramen , at the base of the  skull . It is somewhat dilated at its origin, which is called the  superior bulb .


This vein also has a common trunk into which drains the anterior branch of the  retromandibular vein , the  facial vein , and the  lingual vein .


It runs down the side of the neck in a vertical direction, being at one end lateral to the  internal carotid artery , and then lateral to the  common carotid artery , and at the root of the neck, it unites with the  subclavian vein  to form the  brachiocephalic vein  (innominate vein); a little above its termination is a second dilation, the  inferior bulb .


Above, it lies upon the  rectus capitis lateralis , behind the  internal carotid artery  and the nerves passing through the  jugular foramen . Lower down, the vein and artery lie upon the same plane, the  glossopharyngeal  and  hypoglossal  nerves passing forward between them. The  vagus nerve  descends between and behind the  vein  and the  artery  in the same sheath (the  carotid sheath ), and the  accessory  runs obliquely backward,  superficial  or deep to the vein.


At the root of the neck, the  right internal jugular vein  is a little distance from the  common carotid artery , and crosses the first part of the  subclavian artery , while the  left internal jugular vein  usually overlaps the common carotid artery.


The left vein is generally smaller than the right, and each contains a pair of  valves , which exist about 2.5 cm above the termination of the vessel.


In 9–12% of the Western population, the size, shape or course of the internal jugular vein is abnormal. [ 1 ]  Variants identified including veins markedly smaller, or not functionally present. [ 2 ]  The mean diameter is 10 mm, but may range between 5 and 35 mm. [ 3 ]


The jugular veins are relatively superficial and not protected by tissues such as  bone  or  cartilage . This makes them susceptible to damage. Due to the large volumes of blood that flow through the jugular veins, damage to the jugulars can quickly cause significant blood loss, which can lead to hypovolæmic shock and then death if not treated.


As there is one pair of valves between the  right atrium  of the heart and the internal jugular, blood can flow back into the internal jugular when the pressure in the atrium is sufficiently high. This can be seen from the outside, and allows one to estimate the pressure in the atrium. The pulsation seen is called the  jugular venous pressure , or JVP. This is normally viewed with the patient at 45 degrees turning his/her head slightly away from the observer. The JVP can be raised in a number of conditions: [ 4 ]


The JVP can also be artificially raised by applying pressure to the liver (the  hepatojugular reflux ). This method is used to locate the JVP and distinguish it from the carotid pulse. Unlike the carotid pulse, the JVP is impalpable.


As the internal jugular is large, central and relatively superficial, it is often used to place  central venous lines . Such a line may be inserted for several reasons, such as to accurately measure the central venous pressure or to administer fluids when a line in a peripheral vein would be unsuitable (such as during resuscitation when peripheral veins are hard to locate). [ 5 ]


Because the internal jugular rarely varies in its location, it is easier to find than other veins. However, sometimes when a line is inserted the jugular is missed and other structures such as the  carotid artery , lung or the  vagus nerve  (CN X) are punctured, and damage is caused to these structures.


This article incorporates text in the  public domain  from  page 648  of the 20th edition of   Gray's Anatomy   (1918)


A  jugular foramen  is one of the two (left and right) large  foramina  (openings) in the  base of the skull , located behind the  carotid canal . It is formed by the  temporal bone  and the  occipital bone . It allows many structures to pass, including the  inferior petrosal sinus , three  cranial nerves , the  sigmoid sinus , and meningeal arteries.


The jugular foramen is formed in front by the  petrous  portion of the  temporal bone , and behind by the  occipital bone . [ 1 ]  It is generally slightly larger on the right side than on the left side.


The jugular foramen may be subdivided into three compartments, each with their own contents.


An alternative imaging based subclassification exists, delineated by the  jugular spine  which is a bony ridge partially separating the jugular foramen into two parts:


Obstruction of the jugular foramen can result in  jugular foramen syndrome . [ 2 ] [ 3 ]


This article incorporates text in the  public domain  from  page 181  of the 20th edition of   Gray's Anatomy   (1918)


The  jugular fossa  is a deep depression ( fossa ) in the inferior part of the  temporal bone  at the  base of the skull . It lodges the bulb of the  internal jugular vein .


The jugular fossa is located in the  temporal bone , posterior to the  carotid canal  and the  cochlear aqueduct .


In the bony ridge dividing the carotid canal from the jugular fossa is the small inferior tympanic canaliculus for the passage of the tympanic branch of the  glossopharyngeal nerve . [ 1 ]


In the lateral part of the jugular fossa is the  mastoid canaliculus  for the entrance of the  auricular branch  of the  vagus nerve . [ 1 ]


Behind the jugular fossa is a quadrilateral area, the jugular surface, covered with cartilage in the fresh state, and articulating with the jugular process of the  occipital bone . [ 1 ]


The jugular fossa has variable depth and size in different skulls.


The jugular fossa lodges the bulb of the  internal jugular vein . [ 1 ]


Abnormally shaped jugular fossae may cause ear problems. [ 2 ]  If it lies close to the  cochlea , it may cause  tinnitus . [ 2 ]  A high jugular fossa may be linked to  Ménière's disease . [ 2 ]


The  jugular process  is a quadrilateral or triangular bony plate projecting lateralward from the posterior half of the  occipital condyle ; it is a part of the  lateral part of the occipital bone . [ 1 ]


The jugular process is excavated in front by the jugular notch of occipital bone (which forms the posterior part of the  jugular foramen ). The posterolateral side of the jugular formanen is divided from the anteromedial side by the  intrajugular process of occipital bone . [ 1 ]


The jugular process serves as the insertion of the  rectus capitis lateralis . [ 1 ]


Killian's dehiscence  (also known as  Killian's triangle ) is a triangular area in the wall of the  pharynx  between the cricopharyngeus and thyropharyngeus which are the two parts of the inferior constrictors(also see  Pharyngeal pouch ). It can be seen as a locus minoris resistentiae.
A similar triangular area between circular fibres of the cricopharyngeus and longitudinal fibres of the esophagus is  Lamier's   triangle  or  Lamier-hackermann's area .


It represents a potentially weak spot where a pharyngoesophageal diverticulum ( Zenker's diverticulum ) is more likely to occur. [ 1 ]


It is named after the German ENT surgeon  Gustav Killian . [ 2 ]


The  lacrimal glands  are paired  exocrine glands , one for each  eye , found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the  tear  film. [ 1 ]  In humans, they are situated in the upper lateral region of each  orbit , in the  lacrimal fossa  of the orbit formed by the frontal bone. [ 2 ]  Inflammation of the lacrimal glands is called  dacryoadenitis . The lacrimal gland produces tears which are secreted by the lacrimal ducts, and flow over the ocular surface, and then into canals that connect to the  lacrimal sac . From that sac, the tears drain through the  lacrimal duct  into the nose.


Anatomists divide the gland into two sections, a palpebral lobe, or portion, and an orbital lobe or portion. [ 3 ]  The smaller  palpebral lobe  lies close to the eye, along the inner surface of the eyelid; if the upper  eyelid  is everted, the palpebral portion can be seen.


The orbital lobe of the gland, contains fine  interlobular ducts  that connect the orbital lobe and the palpebral lobe. [ 4 ]  They unite to form three to five main secretory ducts, joining five to seven ducts in the palpebral portion before the secreted fluid may enter on the surface of the eye.  Tears secreted collect in the fornix conjunctiva of the upper lid, and pass over the eye surface to the  lacrimal puncta , small holes found at the inner corner of the eyelids.  These pass the tears through the  lacrimal canaliculi  on to the  lacrimal sac , in turn to the  nasolacrimal duct , which dumps them out into the nose. [ 5 ]


Lacrimal glands are also present in other  mammals , such as horses.


The lacrimal gland is a compound  tubuloacinar gland , it is made up of many  lobules  separated by  connective tissue , each lobule contains many  acini . The acini composed of large serous cells which, produce a watery serous secretion, serous cells are filled with lightly stained secretory granules and surrounded by well-developed myoepithelial cells and a sparse, vascular stroma.
Each acinus consists of a grape-like mass of  lacrimal gland cells  with their apices pointed to a central  lumen .


The central lumen of many of the units converge to form  intralobular ducts , and then they unite to form interlobular ducts. The gland lacks  striated ducts .


The lacrimal gland receives blood from the  lacrimal artery , which is a branch of the  ophthalmic artery . Blood from the gland drains to the  superior ophthalmic vein .


No lymphatic vessels have been observed draining the lacrimal gland.


The lacrimal gland is innervated by the  lacrimal nerve , which is the smallest branch of the  ophthalmic nerve , itself a branch of the  trigeminal nerve  (CN V). After the lacrimal nerve branches from the ophthalmic nerve it receives a communicating branch from the  zygomatic nerve . This communicating branch carries postganglionic parasympathetic axons from the  pterygopalatine ganglion . The lacrimal nerve passes anteriorly in the orbit and through the lacrimal gland providing parasympathetic and sympathetic innervation to it.


The parasympathetic innervation to the lacrimal gland is a complex pathway which traverses through numerous structures in the head. Ultimately this two-neuron pathway involving both a preganglionic and postganglionic parasympathetic neuron increases the secretion of lacrimal fluid from the lacrimal gland. The preganglionic parasympathetic neurons are located in the  superior salivatory nucleus . They project axons which exit the brainstem as part of the  facial nerve  (CN VII). Within the  facial canal  at the  geniculate ganglion  the axons branch from the facial nerve forming the  greater petrosal nerve . This nerve exits the facial canal through the  hiatus for the greater petrosal nerve  in the  petrous part of the temporal bone . It emerges to the  middle cranial fossa  and travels anteromedially to enter the  foramen lacerum . Within the foramen lacerum it joins to the  deep petrosal nerve  to form the  nerve of the pterygoid canal  and then passes through this canal. It emerges in the pterygopalatine fossa and enters the pterygopalatine ganglion where the preganglionic parasympathetic axons synapse with the postganglionic parasympathetic neurons. The postganglionic neurons then send axons which travel with the zygomatic nerve to enter the inferior orbital fissure. As the zygomatic nerve travels anteriorly in the orbit it sends a communicating branch to the lacrimal nerve which carries the postganglionic parasympathetic axons. The lacrimal nerve completes this long pathway by travelling through the lacrimal gland and sending branches to which it provides parasympathetic innervation to increase the secretion of lacrimal fluid.


Sympathetic innervation to the lacrimal gland is of less physiologic importance than the parasympathetic innervation, however there are noradrenergic axons found within the lacrimal gland. Their cell bodies are located in the superior cervical ganglion.


In contrast to the normal moisture of the eyes or even crying, there can be persistent dryness, scratching, itchiness and burning in the eyes, which are signs of dry eye syndrome (DES) or keratoconjunctivitis sicca (KCS). With this syndrome, the lacrimal glands produce less lacrimal fluid, which mainly occurs with aging or certain medications. The Schirmer test, conducted by placing a thin strip of filter paper at the edge of the eye, can be used to determine the level of dryness of the eye. Many medications or diseases that cause dry eye syndrome can also cause hyposalivation with xerostomia. Treatment varies according to aetiology and includes avoidance of exacerbating factors, tear stimulation and supplementation, increasing tear retention, eyelid cleansing, and treatment of eye inflammation. [ 6 ]


In addition, the following can be associated with lacrimal gland pathology:


The  lacrimal sac  or  lachrymal sac [ 1 ]  is the upper dilated end of the  nasolacrimal duct , [ 2 ]  and is lodged in a deep groove formed by the  lacrimal bone  and  frontal process of the maxilla . It connects the  lacrimal canaliculi , which drain tears from the eye's surface, and the  nasolacrimal duct , which conveys this fluid into the nasal cavity. [ 3 ]  Lacrimal sac occlusion leads to  dacryocystitis .
 [ 4 ]


It is oval in form and measures from 12 to 15 mm. in length; its upper end is closed and rounded; its lower is continued into the nasolacrimal duct.


Its superficial surface is covered by a fibrous expansion derived from the  medial palpebral ligament , and its deep surface is crossed by the lacrimal part of the  orbicularis oculi , which is attached to the crest on the lacrimal bone.


Like the nasolacrimal duct, the sac is lined by  stratified columnar epithelium  with mucus-secreting  goblet cells , with surrounding connective tissue. The Lacrimal Sac also drains the eye of debris and microbes.


It serves as a reservoir for overflow of tears, in which the lacrimal sac pumps inward and outward driven by the  orbicularis  muscle during blinking.


The lacrimal sac can be imaged by  dacrocystography , in which  radiocontrast  is injected, followed by  X-ray imaging .


This article incorporates text in the  public domain  from  page 1028  of the 20th edition of   Gray's Anatomy   (1918)


Laryngitis  is  inflammation  of the  larynx  (voice box). [ 1 ]  Symptoms often include a  hoarse voice  and may include  fever , cough, pain in the front of the neck, and  trouble swallowing . [ 1 ] [ 2 ]  Typically, these last under 2 weeks. [ 1 ]


Laryngitis is categorized as  acute  if it lasts less than 3 weeks and  chronic  if symptoms last more than 3 weeks. [ 1 ]  Acute cases usually occur as part of a  viral upper respiratory tract infection , [ 1 ]  other infections, and trauma such as from coughing or other causes. [ 1 ]  Chronic cases may occur due to  smoking ,  tuberculosis ,  allergies ,  acid reflux ,  rheumatoid arthritis , or  sarcoidosis . [ 1 ] [ 3 ]  The underlying mechanism involves irritation of the  vocal cords . [ 2 ]


Concerning signs that may require further investigation include  stridor , history of  radiation therapy  to the neck, trouble swallowing, duration of more than 3 weeks, and a history of smoking. [ 1 ]  If concerning signs are present. the vocal cords should be examined via  laryngoscopy . [ 1 ]  Other conditions that can produce similar symptoms include  epiglottitis ,  croup , inhaling a  foreign body , and  laryngeal cancer . [ 1 ] [ 4 ]


The acute form of the infection, or acute laryngitis, generally resolves without specific treatment. [ 1 ]  Resting the voice and sufficient fluids may help. [ 1 ]   Antibiotics  generally do not appear to be useful in the acute form. [ 5 ]  The acute form is common while the chronic form of the infection, or chronic laryngitis, is not. [ 1 ]  Chronic laryngitis occurs most often in middle age and is more common in men than women. [ 6 ]


The primary symptom of laryngitis is a hoarse voice. [ 7 ] : 108   Because laryngitis can have various causes, other signs and symptoms may vary. [ 8 ]  They can include:


Aside from a hoarse-sounding voice, changes to pitch and volume may occur with laryngitis. Speakers may experience a lower or higher pitch than normal, depending on whether their vocal folds are swollen or stiff. [ 1 ] [ 9 ]  They may also have breathier voices, as more air flows through the space between the vocal folds (the  glottis ), quieter volume, [ 10 ]  and a reduced range. [ 1 ]


Laryngitis can be infectious as well as noninfectious in origin. The resulting inflammation of the vocal folds results in a distortion of the sound produced there. [ 1 ]  It normally develops in response to either an infection, trauma to the vocal folds, or allergies. [ 3 ]  Chronic laryngitis may also be caused by more severe problems, such as nerve damage, sores, and polyps, or hard and thick lumps  (nodules ) on the vocal cords. [ 11 ]


Diagnosis of different forms of acute laryngitis include:


The larynx itself will often show  erythema  (reddening) and  edema  (swelling). This can be seen with  laryngoscopy  or  stroboscopy  (method depends on the type of laryngitis). [ 7 ]  Stroboscopy may be relatively normal or may reveal asymmetry, aperiodicity, and reduced mucosal wave patterns. [ 22 ]


Other features of the laryngeal tissues may include [ citation needed ]


Some signs and symptoms indicate the need for early referral. [ 1 ]  These include:


Treatment is often supportive in nature, and depends on the severity and type of laryngitis (acute or chronic). [ 1 ]  General measures to relieve symptoms of laryngitis include behavior modification, hydration, and humidification. [ 1 ]


Vocal hygiene (care of the voice) is very important to relieve symptoms of laryngitis. Vocal hygiene involves measures such as resting the voice, drinking sufficient water, reducing caffeine and alcohol intake, stopping smoking, and limiting throat clearing. [ 1 ]


In general, acute laryngitis treatment involves vocal hygiene, painkillers ( analgesics ), humidification, and antibiotics. [ 1 ] [ 5 ]


The suggested treatment for viral laryngitis involves vocal rest,  pain medication , and mucolytics for frequent coughing. [ 7 ]  Home remedies such as tea and honey may also be helpful. [ 1 ]  Antibiotics are not used for treatment of viral laryngitis. [ 1 ] [ 23 ]


Antibiotics  may be prescribed for bacterial laryngitis, especially when symptoms of upper respiratory infection are present. [ 7 ]  However, the use of antibiotics is highly debated for acute laryngitis. This relates to issues of effectiveness, side effects, cost, and possibility of antibiotic resistance patterns. Overall, antibiotics do not appear to be very effective in the treatment of acute laryngitis. [ 5 ]


In severe cases of bacterial laryngitis, such as supraglottitis or epiglottitis, there is a higher risk of the airway becoming blocked. [ 7 ]  An urgent referral to a physician should be made to manage the airway. [ 1 ]  Treatment may involve humidification,  corticosteroids , intravenous antibiotics, and nebulised adrenaline. [ 7 ]


Fungal laryngitis can be treated with oral antifungal tablets and antifungal solutions. [ 1 ] [ 7 ]  These are typically used for up to 3 weeks and treatment may need to be repeated if the fungal infection returns. [ 7 ]


Laryngitis caused by excessive use or misuse of the voice can be managed through vocal hygiene measures. [ citation needed ]


Laryngopharyngeal reflux  treatment primarily involves behavioral management and medication. [ 1 ] [ 7 ]  Behavioral management involves aspects such as:


Anti-reflux medications may be prescribed for patients with signs of chronic laryngitis and hoarse voice. [ 24 ]  If anti-reflux treatment does not result in a decrease of symptoms, other possible causes should be examined. [ 1 ]  Over-the-counter medications for neutralizing acids ( antacids ) and acid suppressants ( H-2 blockers ) may be used. [ 7 ]  Antacids are often short-acting and may not be sufficient for treatment. [ 7 ]   Proton pump inhibitors  are an effective type of medication. [ 7 ]  These should only be prescribed for a set period of time, after which the symptoms should be reviewed. [ 1 ]  Proton pump inhibitors do not work for everyone. A physical reflux barrier (e.g., Gaviscon Liquid) may be more appropriate for some. [ 1 ]  Antisecretory medications (i.e., ulcers) can have several side-effects. [ 1 ]


When appropriate, anti-reflux surgery may benefit some individuals. [ 1 ]


When treating allergic laryngitis, topical nasal steroids and  immunotherapy  have been found to be effective for  allergic rhinitis . [ 7 ]   Antihistamines  may also be helpful, but can create a dryness in the larynx. [ 7 ]  Inhaled steroids that are used for a long period can lead to problems with the larynx and voice. [ 7 ]


Mucous membrane pemphigoid  may be managed with medication ( cyclophosphamide  and  prednisolone ). [ 1 ]


Sarcoidosis  is typically treated with  systemic corticosteroids . Less frequently used treatments include intralesional injections or laser resection. [ 1 ]


Acute laryngitis may persist, but will typically resolve on its own within 2 weeks. [ 1 ]  Recovery is likely to be quick if the patient follows the treatment plan. [ 25 ]  In viral laryngitis, symptoms can persist for an extended period, even when upper respiratory tract inflammation has been resolved. [ 23 ]


Laryngitis that continues for more than 3 weeks is considered  chronic . [ 1 ]  If laryngeal symptoms last for more than 3 weeks, a referral to a physician should be made for further examination, including direct  laryngoscopy . [ 1 ]  The prognosis for chronic laryngitis varies depending on the cause of the laryngitis. [ 25 ]


Laryngology  is a branch of  medicine  that deals with disorders,  diseases  and  injuries  of the  larynx , colloquially known as the voice box. Laryngologists treat disorders of the larynx, including diseases that affects the voice, swallowing, or upper airway. Common conditions addressed by laryngologists include  vocal fold nodules  and  cysts ,  laryngeal cancer ,  spasmodic dysphonia ,  laryngopharyngeal reflux ,  papillomas , and voice misuse/abuse/overuse syndromes.  Dysphonia /hoarseness;  laryngitis  (including  Reinke's edema ,  Vocal cord nodules  and  polyps ); * Spasmodic dysphonia ;  dysphagia ;  Tracheostomy ;  Cancer of the larynx ; and  vocology  (the science and practice of voice habilitation) are included in laryngology.


The word "laryngology" is derived from:


Laryngospasm  is an uncontrolled or involuntary muscular contraction ( spasm ) of the  vocal folds . [ 1 ]  It may be triggered when the  vocal cords  or the area of the  trachea  below the vocal folds detects the entry of water, mucus, blood, or other substance.  It may be associated with  stridor  or  retractions .


Laryngospasm is characterized by involuntary spasms of the laryngeal muscles. It is associated with difficulty or inability to breathe or speak,  retractions , a feeling of suffocation, which may be followed by hypoxia-induced loss of consciousness. [ 2 ]  It may be followed by paroxysmal coughing and in partial laryngospasms, a stridor may be heard. [ 3 ]  It requires prompt identification to avoid possibly fatal complications. It may present with loss of end-tidal carbon dioxide (for mechanically ventilated patients), chest or neck retractions and paradoxical chest wall movements. [ 3 ]


The condition typically lasts less than 60 seconds, but in cases of partial blocking it may last 20 to 30 minutes and hinder  inspiration , while  exhalation  remains easier. [ 1 ]


Laryngospasm is a primitive protective airway reflex that functions to protect against  aspiration . However, it may be detrimental if there is sustained closure of the  glottis  resulting in blockage of respiration that hinders the free flow of air. It may be triggered when the  vocal cords  or the area of the  trachea  below the vocal folds detects the entry of water, mucus, blood, or other substance.   [ 1 ]


It is most often reported 1) post-operatively after endotracheal extubation or 2) after sudden reflux of gastric contents. [ 2 ]   [ 4 ] [ 1 ]   It is common in drowning. It is estimated that in 10% of cases of drowning as a response to inhalation of water, death occurs due to asphyxia due to laryngospasm without any water in the lungs. [ 5 ]  It is also a symptom of  hypoparathyroidism . [ 6 ]  It can sometimes occur during sleep, waking up the affected person. These episodic interruptions of sleep have been attributed to acute irritation due to gastro-oesophageal reflux. [ 2 ] [ 7 ]  Laryngospasm is also an unlikely but possible side effect of  ketamine  administration. [ 8 ]  Laryngospasm may happen in people with neurological disease. [ 9 ]


In children, rapid detection and management are imperative to prevent deadly complications such as cardiac arrest, hypoxia and bradycardia. [ 10 ]


Patients with a history of significant aspiration, asthma, exposure to airway irritants (smoke, dust, mold, fumes, use of  Desflurane ), upper respiratory infections, airway anomalies, light anesthesia and patients with acute mental status depression may be at increased risk. [ 2 ] [ 4 ]


When gastroesophageal reflux disease (GERD) is the trigger, treatment of GERD can help manage laryngospasm. Proton pump inhibitors such as  Dexlansoprazole  (Dexilant),  Esomeprazole  (Nexium), and  Lansoprazole  (Prevacid) reduce the production of stomach acids, making reflux fluids less irritant.  Prokinetic agents  reduce the amount of acid available by stimulating movement in the digestive tract. [ 2 ]


Patients who are prone to laryngospasm during illness can take measures to prevent irritation such as antacids to avoid acid reflux. [ 3 ]


For acute context, making an upright position of the upper part of the body has been shown to shorten the spasm episodes.  Fixation  of  the arms  on  stabilization  of  the  body  and  slowing  of  breathing is also recommended. [ 3 ]


Incidence has been estimated at approximately 1% in both adult and pediatric populations. Its incidence is reported to be more than triple in the very young (birth to 3 months of age), increasing to 10% in those with  reactive airways . Other sub-populations with high incidence of laryngospams include patients undergoing tonsillectomy and adenoidectomy (25%). [ 11 ]


It is likely that more than 10% of  drownings  involve laryngospasm, but the evidence suggests that it is not usually effective at preventing water from entering the trachea. [ 12 ]


Most minor laryngospasm get better on its own for most people. [ 1 ]


Laryngospasm is one of the most common intraoperative complications. It may be life-threatening as it involves reflex closure of the laryngeal muscles and thus results in inability to ventilate the patient. [ 13 ]  Treatment requires clearing secretions from the  oropharynx , applying  continuous positive airway pressure  with 100%  oxygen , followed by deepening the plane of anaesthesia with  propofol , and/or paralyzing with  succinylcholine . [ 11 ]


The  lesser palatine nerves  ( posterior palatine nerve ) are branches of the  maxillary nerve  (CN V 2 ). They descends through the  greater palatine canal  alongside the greater palatine nerve, and emerge (separately) through the  lesser palatine foramen  to pass posteriorward. [ 1 ]  They supply the  soft palate ,  tonsil , [ 1 ] [ 2 ]  and  uvula . [ 2 ]


The  lesser petrosal nerve  (also known as the  small superficial petrosal nerve ) is the  general visceral efferent  (GVE) nerve conveying pre-ganglionic  parasympathetic  secretomotor fibers for the  parotid gland  from the  tympanic plexus  to the  otic ganglion  (where they synapse). It passes out of the tympanic cavity through the petrous part of the temporal bone into the middle cranial fossa of the cranial cavity, then exits the cranial cavity through its own canaliculus to reach the infratemporal fossa.


Cell bodies of the lesser petrosal nerve are situated in the  inferior salivatory nucleus , and are conveyed first by the  glossopharyngeal nerve (CN IX)  and then by the  tympanic nerve  to the tympanic plexus.


The nucleus of the lesser petrosal nerve is the  inferior salivatory nucleus . [ citation needed ]  The lesser petrosal nerve may be considered a continuation of the  tympanic nerve . [ 1 ]


After arising in the  tympanic plexus , the lesser petrosal nerve passes anterior-ward, then through the  hiatus for lesser petrosal nerve  on the anterior surface of the  petrous part  of the  temporal bone  into the  middle cranial fossa . [ 2 ]


It runs across the floor of this fossa [ 2 ]  along a groove oriented in the direction the  foramen ovale  and situated parallel and anterolateral to the groove for the  greater petrosal nerve  and its groove. [ 3 ] : 509


It exits the skull via canaliculus innominatus [ 4 ]  and enters the  infratemporal fossa . In the fossa, its fibres synapse at the  otic ganglion . Post-ganglionic fibres then exit the ganglion to briefly travel along with the  auriculotemporal nerve  (a branch of the  mandibular nerve (CN V 3 ) ) before entering the substance of the  parotid gland . [ citation needed ]


The lesser petrosal nerve distributes its post-ganglionic parasympathetic (GVE) fibers to the parotid gland via the intraparotid plexus (or  parotid plexus ), the branches from the facial nerve in the parotid gland. [ citation needed ]


This article incorporates text in the  public domain  from the 20th edition of   Gray's Anatomy   (1918)


The  levator labii superioris  ( pl. :  levatores labii superioris , also called  quadratus labii superioris ,  pl. :  quadrati labii superioris ) is a  muscle  of the  human body  used in  facial expression .  It is a broad sheet, the origin of which extends from the side of the  nose  to the  zygomatic bone . [ 1 ]


Its medial fibers form the  angular head  (also known as the  levator labii superioris alaeque nasi muscle [ 2 ] ) which arises by a pointed extremity from the upper part of the  frontal process  of the  maxilla  and passing obliquely downward and lateralward divides into two slips.


One of these is inserted into the  greater alar cartilage  and skin of the nose; the other is prolonged into the lateral part of the  upper lip , blending with the infraorbital head and with the  orbicularis oris .


The intermediate portion or  infraorbital head  arises from the lower margin of the  orbit  immediately above the infraorbital foramen, some of its fibers being attached to the  maxilla , others to the  zygomatic bone .


Its fibers converge, to be inserted into the muscular substance of the upper lip between the angular head and the  levator anguli oris .


The lateral fibers, forming the  zygomatic head  (also known as the  zygomaticus minor muscle [ 3 ] ) arise from the malar surface of the  zygomatic bone  immediately behind the  zygomaticomaxillary suture  and pass downward and medialward to the upper lip.


Its main function is to elevate the upper lip. [ 4 ]


This article incorporates text in the  public domain  from  page 383  of the 20th edition of   Gray's Anatomy   (1918)


The  major alar cartilage  ( greater alar cartilage ) ( lower lateral cartilage ) is a thin, flexible plate, situated immediately below the  lateral nasal cartilage , and bent upon itself in such a manner as to form the  medial wall  and lateral wall of the  nostril  of its own side.


The portion which forms the  medial wall  (crus mediale) is loosely connected with the corresponding portion of the opposite cartilage, the two forming, together with the thickened  integument  and subjacent tissue, the  nasal septum .


The part which forms the lateral wall (crus laterale) is curved to correspond with the  ala of the nose ; it is oval and flattened, narrow behind, where it is connected with the  frontal process of the maxilla  by a tough fibrous membrane, in which are found three or four small cartilaginous plates, the  lesser alar cartilages  (cartilagines alares minores; sesamoid cartilages).


Above, it is connected by fibrous tissue to the lateral cartilage and front part of the  cartilage of the septum ; below, it falls short of the margin of the nostril, the ala being completed by fatty and fibrous tissue covered by  skin .


In front, the greater alar cartilages are separated by a notch which corresponds with the apex of the nose.


This article incorporates text in the  public domain  from  page 993  of the 20th edition of   Gray's Anatomy   (1918)


The  malleus , or  hammer , is a hammer-shaped small bone or  ossicle  of the  middle ear . It connects with the  incus , and is attached to the inner surface of the  eardrum . The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibrations from the eardrum to the  incus  (anvil).


The malleus is a bone situated in the middle ear. It is the first of the three  ossicles , and attached to the  eardrum  (tympanic membrane). The head of the malleus is the large protruding section, which attaches to the  incus . The head connects to the neck of malleus. The bone continues as the handle (or manubrium) of malleus, which connects to the tympanic membrane. [ 1 ]  Between the neck and handle of the malleus, lateral and anterior processes emerge from the bone. [ 2 ] [ 3 ]  The bone is oriented so that the head is superior and the handle is inferior. [ 3 ]


Embryologically, the malleus is derived from the first  pharyngeal arch  along with the  incus . [ 3 ]  In humans it grows from  Meckel's cartilage . [ 3 ]


The malleus is one of three  ossicles  in the  middle ear  which transmit sound from the  tympanic membrane (ear drum)  to the  inner ear . The malleus receives vibrations from the tympanic membrane and transmits this to the incus. [ 2 ]


The malleus may be  palpated  by  surgeons  during  ear surgery . [ 1 ]  It may become fixed in place due to surgical complications, causing hearing loss. [ 1 ]  This may be corrected with further surgery. [ 1 ]


Several sources  attribute the discovery of the malleus to the  anatomist  and  philosopher   Alessandro Achillini . [ 4 ] [ 5 ]  The first brief written description of the malleus was by  Berengario da Carpi  in his  Commentaria super anatomia Mundini  (1521). [ 6 ]   Niccolo Massa 's  Liber introductorius anatomiae [ 7 ]  described the malleus in slightly more detail and likened both it and the  incus  to little hammers terming them  malleoli . [ 8 ]


The  malleus  is unique to mammals, and  evolved from a lower jaw bone  in basal  amniotes  called the  articular , which still forms part of the jaw joint in reptiles and birds. [ 9 ] [ 10 ]


In  neuroanatomy , the  mandibular nerve  ( V 3 ) is the largest of the three divisions of the  trigeminal nerve , the fifth  cranial nerve  (CN V). Unlike the other divisions of the trigeminal nerve ( ophthalmic nerve ,  maxillary nerve ) which contain only  afferent fibers , the mandibular nerve contains both afferent and  efferent fibers . These nerve fibers innervate structures of the  lower jaw  and face, such as the  tongue ,  lower lip , and  chin . The mandibular nerve also innervates the  muscles of mastication . [ 1 ]


The large sensory root of mandibular nerve emerges from the lateral part of the  trigeminal ganglion  and exits the  cranial cavity  through the  foramen ovale . The motor root (Latin:  radix motoria  s.  portio minor ), the small motor root of the  trigeminal nerve , passes under the trigeminal ganglion and through the  foramen ovale  to unite with the sensory root just outside the  skull . [ 2 ] [ better source needed ]


The mandibular nerve immediately passes between  tensor veli palatini , which is medial, and  lateral pterygoid , which is lateral, and gives off a  meningeal branch  (nervus spinosus) and the  nerve to medial pterygoid  from its medial side. The nerve then divides into a small anterior division and a large posterior division.


The mandibular nerve gives off the following branches:


Anterior Division


(Motor Innervation -  Muscles of mastication )


(Sensory Innervation)


Posterior Division


Lingual Split
(general sensory innervation ( not  special sensory for taste))


Inferior Alveolar Split
(Motor Innervation)


Auriculotemporal Split


Mandibular setback surgery  is a  surgical procedure  performed along the  occlusal plane  to prevent bite opening on the anterior or posterior teeth and retract the lower jaw for both functional and aesthetic effects in patients with  mandibular prognathism . [ 1 ] [ 2 ]  It is an orthodontic surgery that is a form of  reconstructive plastic surgery. [ 3 ]  There are three main types of procedures for mandibular setback surgery: Bilateral Sagittal Split Osteotomy (BSSO), Intraoral Vertical Ramus Osteotomy (IVRO) and Extraoral Ramus Osteotomy (EVRO), depending on the magnitude of mandibular setback for each patient. Postoperative care aims to minimise postoperative complications, complications includes  bite  changes,  relapse  and  nerve injury .


The origin of orthognathic surgery was introduced by  Simon P. Hullihen  in 1849. [ 4 ]  Upon Hullihen's discovery of the procedure, many surgeons further investigated and modified approaches to correct mandibular prognathism. [ 5 ]  Vilray Blair and Edward H. Angle collaborated to introduce osteotomy to the mandibular body with a horizontal incision, marking the beginning of orthognathic surgery. [ 6 ]  With these notable modifications in surgical procedures for prognathism, BSSO, IVRO and EVRO are procedures used in practise to treat individuals with dentofacial deformities. VRO was first introduced as EVRO by Caldwell and Letterman and further modified into IVRO by Moose in 1964. [ 7 ] [ 8 ] [ 9 ] [ 10 ]  BSSO was then introduced by Obwegeser in 1959. [ 11 ]


Mandible  is a movable solitary bone forming the lower jaw. [ 12 ]  It is composed of a mandibular body and two mandibular rami (singular: ramus [ 13 ] ) on bilateral sides of the face. [ 14 ]  The mandibular ramus contains the  mandibular foramen , which is where the  inferior alveolar nerve  and  artery  enters. [ 14 ]  Each end of the ramus has a projection that articulates with the  temporal bones  via  temporomandibular joint  called  mandibular condyle . [ 14 ]


Lingula  is superior to mandibular foramen on the mandibular ramus, which often acts as a recognisable feature for surgical procedures. [ 15 ] [ 16 ]


BSSO and IVRO are the two most common types of procedures used for mandibular setback surgery while EVRO is carried out for specific cases.


A vertical incision is performed on the inferior and lateral sides of the soft tissue in the mouth at a distance from the adjacent  gums . [ 17 ]  The cut is performed from the mandibular ramus to the mandibular body along the external oblique line, down to the mandibular  first molar  region, and further down the  buccal vestibule  of the mandible. [ 16 ]  A precise cut allows sufficient tissues remained for closing the suture. [ 17 ]   The surrounding soft tissue from the bone is dissected and elevated in a subperiosteal plane to see the mandibular ramus clearly. The mandibular foramen and the lingula must also be exposed without damaging the inferior alveolar nerve. A clamp is used to hold the layers in a fixed position for mandibular osteotomy to be carried out.


The BSSO technique requires two cuts of the mandible utilising an osteotome that is inclined to one side. [ 17 ]  Firstly, the lateral osteotomy starts at the buccal cortex, the bone in the buccal space. This split is done vertically down to the first or second molar region. [ 18 ]  Then the medial osteotomy is done on the lingual cortical bone, which extends to the anterior border of the ramus posterior and to the inferior alveolar canal. [ 16 ]  Subsequently, the fractures of the ramus are split by applying slight force.


Mobilisation of the segments are done to the pre-arranged position and fixed internally with screws and plates. [ 19 ]  BSSO allows rigid fixation and increases stability of mandibular setbacks. However, as the nerve is manipulated to a large extent during the surgery, it increases the chance of patients experiencing neurosensory loss. [ 20 ]  Studies have shown statistically that another type of method, IVRO, can reduce the chance of neurosensory disturbance. [ 21 ]


Firstly, a horizontal incision through the  oral mucosa  along the anterior border of the ramus of mandible within the mouth allows surgeons to reach the underlying bone and tissue of the lower jaw. [ 16 ]  Once the cut opens near the coronoid process and mandibular first molar region, a deeper dissection is done so the  mandibular notch , inferior and posterior of the ramus are visible. [ 16 ]  Then, the IVRO can be performed.


A pair of  retractors  are positioned properly and carefully for clear exposure of the ramus. [ 16 ]  The cutting of the bone is done by surgical  oscillating saw , [ 22 ]  at an angle of 105° precisely behind the body prominence of antilingula, superior to the  sigmoid notch  and inferior to the  mandibular angle . The bone fragment is adjusted to the preoperative planned position, which sets the lower jaw backwards. [ 23 ]  Stabilisation of the jaw at its modified position is then done through wiring. The inter-maxillary fixation is usually kept for around six weeks. [ 16 ]


The IVRO procedure can be performed if the magnitude of the mandibular setback is within 10mm. [ 24 ]  The limitation of the specific range of setback is to prevent postoperative forward relapse and the dislocation of mandibular condylar head. [ 24 ]  When the required adjustment of the jaw exceeds 10mm, patients will most likely undertake the EVRO procedure.


The incision for EVRO is made on the most superficial layer of the skin, approximately 1 to 2 cm below the mandibular angle. [ 25 ] [ 26 ]  The dissection cuts the  platysma  and the  masseter muscle . As the skin dissection is done, a small protrude of the ramus could be observed. This allows the mandible osteotomy to be done safely by avoiding damaging the adjacent nerves. [ 16 ]


The bony cut is made from the sigmoid notch to the mandibular angle with an osteotome. The bony fragment at the proximal end is rearranged and stabilized using screws, plates, or wires. The closure of the wound is done layer by layer. The intermaxillary fixation is usually kept for a week to ten days. [ 25 ]


Compared to BSSO and IVRO, this technique takes the least surgical time as it is performed on the external surface, which allows the surgeons to have easier access and clearer vision. However, the surgical scar that is left behind could be a concern to certain patients.


The mandibular setback surgery can improve masticatory function and facial aesthetics by repositioning the jaw and mouth, which can have a positive effect on the patient's psychosocial well-being. [ 27 ] [ 28 ]


Patients with mandibular prognathism may have difficulty chewing, speaking, and breathing, which can affect their quality of life. [ 17 ]  The mandibular setback surgery improves one's  masticatory muscle  activity and  speech intelligibility . [ 29 ]  The mandibular setback surgery improves functional difficulties caused by mandibular prognathism.


Aesthetic correction is second positive effect of mandibular setback surgery. In particular, it improves the asymmetry of the upper and lower lip in patients with  mandibular prognathism . Patients after the surgery may result in a more pronounced and defined chin by repositioning the jaw. [ 30 ] [ 31 ]  Ultimately, it allows for a more balanced and harmonious facial profile. [ 32 ]


Post-surgery questionnaires results indicated improved psychosocial well-being, self-esteem and social functioning in patients after the mandibular setback surgery. [ 32 ]  There is also a high patient satisfaction rate for the surgery. [ 33 ]  These show how the mandibular setback surgery improves well-being of patients with mandibular prognathism. [ 28 ]


After the setback surgery, a 2-week recovery period is needed for the wires to be closed and inter-maxillary fixation to stabilise the position of the mandible. [ 34 ]  Patients would stay for a minimum of 1 to 2 days and exception may occur if a complication has occurred. Post-operative assessments need to be done for the 2 weeks after the operation.


Gum chewing and patient education exercise post-surgery can improve masticatory function in patient and minimise the risk of complications. [ 35 ] [ 36 ]


More than 40% of patients have complications after mandibular setback surgery. [ 31 ]  Complications include bite changes, nerve injuries and relapse.


Bite changes occur in 20.3% of the cases post-setback surgery. [ 37 ]  Change in pharyngeal airway space and tongue position can have a significant effect on bite changes after mandibular setback surgery and cause obstructive sleep apnea. [ 1 ] [ 38 ] [ 39 ]


The tongue is normally positioned against the roof of the mouth, supporting the upper jaw. After surgery, the change in the position of the tongue affects the position of the jaw, leading to bite changes. [ 40 ]  Bite changes can narrow the pharyngeal airway space after surgery can lead obstructive sleep apnea. [ 41 ]  Incorrect jaw positioning requires additional surgery to reposition the jaw and open up the airway. [ 42 ]


9.2% of the patients who underwent the mandibular setback surgery has found post-surgery relapse. [ 43 ]  This is caused by actions of the condyle resorption. [ 44 ]  Condyle resorption is when the bone tissue is lost in the condyle. Condyle resorption reduces stability of the mandible and cause long term skeletal relapse. [ 45 ] [ 46 ]  When the mandible is not stabilised, it allows movement of the mandible into its pre-operative position, contributing to early relapse. [ 47 ]  Bone fixation procedures will be needed due to the lack of bone healing. [ 48 ]


Nerve injuries occur in 3.7% of the patients after the mandibular setback surgery. [ 49 ]  Cutting and repositioning of the mandible in the surgery can potentially damage nerves in the mandible that is responsible for sensation and movement. Specifically, the inferior alveolar nerve are the commonly affected nerve in the surgery. [ 50 ]  Less common nerves injuries are on the lingual nerve and mental nerve, which are responsible for tongue and chin sensation respectively. The lingual nerve is affected by the wire placement in the molar region. [ 51 ]  The mental nerve injury can be caused by the presence of  bony spurs . A damage in the nerve may require additional therapy to repair the loss of ability in the nerves. [ 52 ]


The  marginal mandibular branch of the facial nerve  arises from the  facial nerve (CN VII)  in the parotid gland at the  parotid plexus . It passes anterior-ward deep to the  platysma  and  depressor anguli oris  muscles. It provides motor innervation to muscles of the  lower lip  and  chin : the  depressor labii inferioris muscle ,  depressor anguli oris muscle , and  mentalis muscle . [ 1 ]  It communicates with the mental branch of the  inferior alveolar nerve . [ citation needed ]


The marginal mandibular nerve may be injured during surgery in the neck region, especially during excision of the submandibular salivary gland or during neck dissections due to lack of accurate knowledge of variations in the course, branches and relations. An injury to this nerve during a surgical procedure can distort the expression of the smile as well as other facial expressions. The marginal mandibular branch of the facial nerve is found superficial to the facial artery and (anterior) facial vein. Thus the facial artery can be used as an important landmark in locating the marginal mandibular nerve during surgical procedures. [ 2 ]  Damage can cause paralysis of the three muscles it supplies, which can cause an asymmetrical smile due to lack of contraction of the  depressor labii inferioris muscle . [ 3 ]  This may be corrected with resection of the muscle, which tends to be successful. [ 3 ]


The  mastoid antrum  ( tympanic antrum ,  antrum mastoideum ,  Valsalva's antrum ) is an air space in the petrous portion of the  temporal bone , communicating posteriorly with the  mastoid cells  and anteriorly with the  epitympanic recess  of the  middle ear  via the  aditus to mastoid antrum  (entrance to the mastoid antrum). These air spaces function as sound receptors, provide voice resonance, act as acoustic insulation and dissipation, provide protection from physical damage and reduce the mass of the cranium. [ citation needed ]
The roof is formed by the tegmen antri which is a continuation of the  tegmen tympani  and separates it from the  middle cranial fossa .
The lateral wall of the antrum is formed by a plate of bone which is an average of 1.5 cm in adults.
The  mastoid air cell   system is a major contributor to middle ear inflammatory diseases. [ 1 ]


In the lateral part of the  jugular fossa  of the  temporal bone  is the  mastoid canaliculus  for the entrance of the  auricular branch  of the  vagus nerve .


This article incorporates text in the  public domain  from  page 144  of the 20th edition of   Gray's Anatomy   (1918)


The  mastoid cells  (also called  air cells of Lenoir  or  mastoid cells of Lenoir ) are air-filled cavities within the  mastoid process  of the  temporal bone  of the  cranium . The mastoid cells are a form of  skeletal pneumaticity . Infection in these cells is called  mastoiditis .


The term  cells  here refers to enclosed spaces, not  cells  as living, biological units.


The mastoid air cells vary greatly in number, shape, and size; they may be extensive or minimal or even absent. [ 1 ] : 746


The cells are typically interconnected and their walls lined by mucosa that is continuous with that of the mastoid antrum and tympanic cavity. [ 1 ] : 746


They may excavate the mastoid process to its tip, and be separated from the  posterior cranial fossa  and  sigmoid sinus  by a mere slip of bone or not at all. They may extend into the  squamous part of temporal bone ,  petrous part of the temporal bone   zygomatic process of temporal bone , and - rarely - the  jugular process of occipital bone ; they may thus come to adjoin many important structures (including the bony labyrinth, tympanic cavity, external acoustic meatus, pharyngotympanic tube, superior jugular bulb, posterior cranial fossa, middle cranial fossa, carotid canal, abducens nerve, sigmoid sinus) to which they may disseminate infection in case of infective mastoiditis. [ 1 ] : 746


The cells receive  innervation [ clarify ]  from the posterior branch of the  meningeal branch of the mandibular nerve (nervus spinosus) , [ 1 ] : 400.e2  [ 2 ] : 364   and branches of the  tympanic plexus . [ 1 ] : 749  [ 2 ] : 366


The cells receive arterial supply from the stylomastoid branch of the  occipital artery  or  posterior auricular artery , and (sometimes) a mastoid branch of the  occipital artery . [ 1 ] : 749


The  superior petrosal sinus  receives venous drainage from the mastoid air cells (mastoid infection may thus lead to a cerebellar abscess). [ 2 ] : 443


At birth, the mastoid is not pneumatized, but becomes aerated before age six. [ 3 ]  At birth, the mastoid antrum is well developed but the air cells are represented only by small diverticula from the antrum. The air cells then gradually extend into the bone of the mastoid during the first years of life. Their most significant enlargements takes place during puberty. [ 1 ] : 746


The air cells are hypothesised to protect the temporal bone and the inner and middle ear against trauma and to regulate air pressure. [ 4 ]


Infections in the middle ear  easily spread into the mastoid air cells through the  aditus ad antrum , resulting in  mastoiditis , a potentially dangerous and life-threatening condition. Infection may then further spread into the middle cranial fossa or posterior cranial fossa, causing meningitis or abscess of adjacent brain tissue. Infection may also spread to muscles of the neck, causing pain and  torticollis . [ 1 ] : 746


The  mastoid foramen  is a hole in the posterior border of the  temporal bone . It transmits an  emissary vein  between the  sigmoid sinus  and the  suboccipital venous plexus , and a small branch of the  occipital artery , the  posterior meningeal artery  to the  dura mater .


The mastoid foramen is a hole in the posterior border of the  temporal bone  of the  skull . [ 1 ]


The opening of the mastoid foramen is an average of 18 mm from the  asterion , [ 2 ]  and around 34 mm from the  external auditory meatus . [ 3 ]  It is typically very narrow. [ 1 ] [ 3 ]  This may be around 2 mm. [ 3 ]


The position and size of this foramen are very variable. [ 1 ] [ 3 ]  It is not always present. [ 1 ] [ 3 ]  Sometimes, it is duplicated on one side or both sides. [ 1 ]  Sometimes, it is situated in the  occipital bone , or in the  suture  between the temporal bone and the occipital bone.


The mastoid foramen transmits:


This article incorporates text in the  public domain  from  page 141  of the 20th edition of   Gray's Anatomy   (1918)


The  mastoid part of the temporal bone  is the posterior (back) part of the  temporal bone , one of the  bones  of the  skull . Its rough surface gives attachment to various  muscles  (via  tendons ) and it has  openings  for  blood vessels . From its borders, the mastoid part  articulates  with two other bones.


The word "mastoid" is derived from the Greek word for " breast ", a reference to the shape of this bone.


Its outer surface is rough and gives attachment to the  occipitalis  and  posterior auricular muscles . It is perforated by numerous  foramina  (holes); for example, the  mastoid foramen  is situated near the posterior border and transmits a vein to the  transverse sinus  and a small branch of the  occipital artery  to the  dura mater . The position and size of this foramen are very variable; it is not always present; sometimes it is situated in the occipital bone, or in the suture between the temporal and the occipital.


The mastoid process is located posterior and inferior to the  ear canal , lateral to the  styloid process , and appears as a conical or pyramidal projection. It forms a bony prominence behind and below the ear. [ 1 ]  It has variable size and form (e.g. it is larger in the  male  than in the  female ). It is also filled with  sinuses , or  mastoid cells . The mastoid process serves for the attachment of the  sternocleidomastoid , the posterior belly of the  digastric muscle ,  splenius capitis , and  longissimus capitis . On the medial side of the process is a deep groove, the mastoid notch, for the attachment of the  digastric muscle ; medial to this is a shallow furrow, the  occipital groove , which lodges the  occipital artery . The  facial nerve  passes close to the mastoid process. [ 2 ]


The inner surface of the mastoid portion presents a deep, curved groove, the  sigmoid sulcus , which lodges part of the  transverse sinus ; in it may be seen in the opening of the  mastoid foramen .


The groove for the transverse sinus is separated from the innermost of the mastoid cells by a very thin lamina of bone, and even this may be partly deficient.


The  superior border  of the mastoid part is broad and serrated, for articulation with the mastoid angle of the parietal.


The  posterior border , also serrated, articulates with the inferior border of the occipital between the lateral angle and  jugular process .


Anteriorly, the mastoid portion is fused with the descending process of the  squama  above; below, it enters into the formation of the  ear canal  and the  tympanic cavity .


A section of the mastoid process shows it to be hollowed out into a number of spaces, the  mastoid cells , which exhibit the greatest possible variety as to their size and number. At the upper and front part of the process, they are large and irregular and contain air, but toward the lower part, they diminish in size, while those at the apex of the process are frequently quite small and contain marrow; occasionally, they are entirely absent, and the mastoid is then solid throughout.


In addition to these a large irregular cavity is situated at the upper and front part of the bone. It is called the  tympanic antrum  and must be distinguished from the mastoid cells, though it communicates with them. Like the mastoid cells, it is filled with air and lined by a prolongation of the mucous membrane of the tympanic cavity, with which it communicates. The tympanic antrum is bounded above by a thin plate of bone, the  tegmen tympani , which separates it from the middle fossa of the  base of the skull , below by the mastoid process, laterally by the squama just below the  temporal line , and medially by the  lateral semicircular canal  of the  internal ear , which projects into its cavity. It opens in front into that portion of the tympanic cavity which is known as the attic or  epitympanic recess . The tympanic antrum is a cavity of some considerable size at the time of birth; the mastoid air cells may be regarded as diverticula from the antrum and begin to appear at or before birth. By the fifth year, they are well-marked, but their development is not completed until toward  puberty .


The mastoid process is absent or rudimentary in the neonatal skull. It forms postnatally (starts to develop after 1 year old), [ citation needed ]  as the sternocleidomastoid muscle develops and pulls on the bone. It usually finishes structural development by 2 years old. [ 3 ]


Because of the late  postnatal development  of the mastoid process, antenatal injuries to the region often recover spontaneously. [ 3 ]  The largest size is found in  South Africans  and least found in North American Indians. [ 4 ]


Rarely, lesions can develop on the mastoid process. [ 5 ]


A  mastoidectomy  is a procedure performed to remove the  mastoid air cells [ 1 ]  near the middle ear. The procedure is part of the treatment for  mastoiditis ,  chronic suppurative otitis media  or  cholesteatoma . [ 2 ]  Additionally, it is sometimes performed as part of other procedures, such as  cochlear implants , [ 3 ]  or to access the middle ear.


Historically,  trephination  was used to potentially relieve intracranial pressures or build-up of pus, with records dating back to pre-historic times. [ 4 ]  Over time, these became formalized as mastoidectomies. Mastoidectomies were used to treat infections such as otitis media, or abnormal skin cell growth near the middle ear. [ 2 ]  Over time, they were adapted to help treat hearing issues such as  tinnitus . [ 5 ]


Mastoidectomies have also been used in the modern practice of placing cochlear implants. [ 6 ]  Additionally, mastoidectomies are occasionally performed with  tympanoplasties  to fix the tympanic membrane. [ 7 ]


The following are possible complications from mastoidectomy procedures: [ 8 ]


In 2018, the International Otology Outcome Group agreed on guidelines defining different mastoidectomies. [ 8 ]  Before this, there was discourse on the proper classifications of the procedure. [ 11 ]


Under the 2018 guidelines, there are the following types of mastoidectomy: [ 12 ]


Also known as  schwartze procedure  or  cortical mastoidectomy  or  canal wall up


Also known as  canal wall down


Used for


Additionally, there are mixed categories, such as M 1a+2a  and M 1b+2a . There is a slight distinction between M 2c  and M 3a  in that M 3a  removes the eardrum before pre auricular pit and cavity closure and blocks the tympanic opening of the  Eustachian tube . [ 12 ]


After the invention of  endoscopic transcanal ear surgery  by  Muaaz Tarabichi , the usage of this procedure has decreased significantly. [ 14 ]


Greek physician  Galen  (AD 129-217) was the first to write in his treatise Hygiene (Italian:  De Sanitate Tuenda ,  English:  On the Preservation of Health ) about ear discharge being a natural secretion form the brain, and the importance of permitting drainage of such fluid. [ 15 ]


The first potential documented case of a mastoidectomy procedure was recorded in 1524 by  Lucas van Leyden  as an incision behind the right ear. Abscess drainage was popularized by  Adam Politzer , considered to be one of the founders of  otology  and initially interpreted Galen's writings on ear discharge to mean that Galen removed infected mastoid regions. [ 16 ]  However, this may have been deliberately misrepresented to justify mastoidectomy procedures to more conservative audiences. [ 17 ]


Additionally, there is controversy whether French physician  Ambroise Paré  was the first to describe a surgical procedure draining an infected ear of  Francis II of France  in 1560. [ 18 ]  Recent studies have shown how there is lack of documentation of this event by French historian Louis Régnier de la Planch, and also lack of mention in Paré's own writings. [ 17 ]


Credit for the first mastoidectomy to remove abscesses is attributed to  Jean-Louis Petit  in the 18th century. [ 19 ]  However soon after this, the procedure fell out of popularity in the 18th century after the death of Justus von Berger in 1791. [ 20 ]  von Berger, the court physician of  Christian VII , died 13 days after a mastoidectomy attempt to fix his right-sided deafness.


The mastoidectomy was revitalized in 1873 following the publication,  Ueber die künstliche Eröffnung des Warzenfortsatzes  (English:  “On the artificial opening of the mastoid process” ), written by  Hermann Schwartze  and his assistant Adolf Eysell. [ 21 ]  In the publication, Schwartze made several recommendations on modernizing the procedure, including replacing older instruments and a new surgical technique. This procedure, using a chisel and gouge, [ 4 ]  is now credited as the "modern mastoid operation" or Schwartze operation. [ 22 ]  Published in the oldest and most known otolaryngology journal of the time,  Archiv für Ohrenheilkunde , the publication became widely disseminated and referenced. [ 23 ]


Mastoiditis  is the result of an infection that extends to the  air cells  of the  skull  behind the ear.  Specifically, it is an inflammation of the  mucosal lining  of the  mastoid antrum  and  mastoid air cell  system inside [ 1 ]  the  mastoid process . The mastoid process is the portion of the  temporal bone  of the skull that is behind the ear. The mastoid process contains open,  air-containing spaces . [ 2 ] [ 3 ]  Mastoiditis is usually caused by untreated acute  otitis media  (middle ear infection) and used to be a leading cause of child mortality. With the development of  antibiotics , however, mastoiditis has become quite rare in developed countries where surgical treatment is now much less frequent and more conservative, unlike former times. [ 2 ]


There is no evidence that the drop in antibiotic prescribing for otitis media has increased the incidence of mastoiditis, raising the possibility that the drop in reported cases is due to a confounding factor such as childhood immunizations against  Haemophilus  and  Streptococcus . Untreated, the infection can spread to surrounding structures, including the brain, causing serious complications. [ 4 ]  While the use of antibiotics has reduced the incidence of mastoiditis, the risk of masked mastoiditis, a subclinical infection without the typical findings of mastoiditis has increased with the inappropriate use of antibiotics and the emergence of  multidrug-resistant bacteria . [ 5 ]


Some common  symptoms  and  signs  of mastoiditis include  pain , tenderness, and swelling in the mastoid region. There may be ear pain ( otalgia ), and the ear or mastoid region may be red (erythematous). Fever or headaches may also be present. Infants usually show  nonspecific symptoms , including  anorexia ,  diarrhea , or  irritability . Drainage from the ear occurs in more serious cases often manifests as brown discharge on the pillowcase upon waking. [ 4 ] [ 6 ]


The pathophysiology of mastoiditis is straightforward: bacteria spread from the middle ear to the  mastoid air cells , where the inflammation causes damage to the bony structures.  Streptococcus pneumoniae ,  Streptococcus pyogenes ,  Staphylococcus aureus ,  Haemophilus influenzae ,  and  Moraxella catarrhalis  are the most common organisms recovered in acute mastoiditis. Organisms that are rarely found are  Pseudomonas aeruginosa  and other Gram-negative aerobic bacilli, and anaerobic bacteria. [ 7 ]   P. aeruginosa,  Enterobacteriaceae,  S. aureus  and  anaerobic bacteria  ( Prevotella ,  Bacteroides ,  Fusobacterium , and  Peptostreptococcus  spp.) are the most common isolates in chronic mastoiditis. [ 8 ]  Rarely,  Mycobacterium  species can also cause the infection. Some mastoiditis is caused by  cholesteatoma , which is a sac of keratinizing squamous epithelium in the middle ear that usually results from repeated middle-ear infections. If left untreated, the cholesteatoma can erode into the mastoid process, producing mastoiditis, as well as other complications. [ 4 ]


The diagnosis of mastoiditis is clinical—based on the  medical history  and  physical examination . Imaging studies provide additional information; The standard method of diagnosis is via  MRI scan  although a  CT scan  is a common alternative as it gives a clearer and more useful image to see how close the damage may have gotten to the brain and facial nerves. Planar (2-D)  X-rays  are not as useful. If there is drainage, it is often sent for  culture , although this will often be negative if the patient has begun taking antibiotics.  Exploratory surgery  is often used as a last resort method of diagnosis to see the mastoid and surrounding areas. [ 2 ] [ 9 ]


If ear infections are treated in a reasonable amount of time, the antibiotics will usually cure the infection and prevent its spread. For this reason, mastoiditis is rare in developed countries. Most ear infections occur in infants as the eustachian tubes are not fully developed and don't drain readily. [ citation needed ]