Multiple meta-analyses of the literature from 2018 showed that CI users have large improvements in quality of life after cochlear implantation. [ 51 ] [ 52 ]  This improvement occurs in many different facets of life that extends beyond communication including improved ability to engage in social activities; decreased mental effort from listening; and improved environmental sound awareness. [ 53 ] [ 54 ] [ 50 ]  Deaf adolescents with cochlear implants attending mainstream educational settings report high levels of scholastic self-esteem, friendship self-esteem, and global self-esteem. [ 55 ]  They also tend to hold mostly positive attitudes towards their cochlear implants, [ 56 ]  and as a part of their identity, a majority either do "not really think about" their hearing loss, or are "proud of it." [ 57 ]  Though advancements in cochlear implant technology have helped patients in their understanding of language, users are still unable to understand suprasegmental portions of language, which includes pitch. [ 58 ]


A study by  Johns Hopkins University  determined that for a three-year-old child who receives them, cochlear implants can save $30,000 to $50,000 in special-education costs for elementary and secondary schools as the child is more likely to be mainstreamed in school and thus use fewer support services than similarly deaf children. [ 59 ]


A 2019 study found that bilateral cochlear implantation was widely regarded as the most beneficial hearing intervention for acceptable candidates, although it is more likely to be performed and reimbursed in children than adults. The study also found that the efficacy of bilateral implantation could be improved by enhancing communication between the two implants and by developing sound coding strategies specifically for bilateral users. [ 60 ]


Early research reviews found that the ability to communicate in spoken language was better the earlier the implantation was performed. The reviews also found that, overall, while cochlear implants provide open-set speech understanding for the majority of implanted profoundly hearing-impaired children, it was not possible to accurately predict the specific outcome of the given implanted child. [ 61 ] [ 62 ] [ 63 ]  Research since then has reported long-term socio-economic benefits for children as well as audiological outcomes including improved sound localization and speech perception. [ 64 ]  A consensus statement from the European Bilateral Pediatric Cochlear Implant Forum also confirmed the importance of bilateral cochlear implantation in children. [ 65 ]  In adults, new research shows that bilateral implantation can improve quality of life and speech intelligibility in quiet and noise. [ 66 ]


A 2015 review examined whether CI implantation to treat people with bilateral hearing loss had any effect on  tinnitus . This review found the quality of evidence to be poor and the results variable: overall total tinnitus suppression rates for patients who had tinnitus prior to surgery varied from 8% to 45% of people who received CI; decrease of tinnitus was seen in 25% to 72%, of people; for 0% to 36% of the people there was no change; increase of tinnitus occurred in between 0% to 25% of patients; and, in between 0 and 10% of cases, people who did not have tinnitus before the procedure, got it. [ 67 ]  Further research found that the electrical stimulation of the CI is at least partly responsible for the general reduction in symptoms. A 2019 study found that although tinnitus suppression in patients with CIs is multifactorial, simply having the CI switched on without any audiological input (while standing alone in a soundproof booth) reduced the symptoms of tinnitus. This would suggest that it is the electrical stimulation that explains the decrease in tinnitus symptoms for many patients, and not only the increased access to sound. [ 68 ]


A 2015 literature review on the use of CI for people with  auditory neuropathy spectrum disorder  found that, as of that date, description and diagnosis of the condition was too heterogeneous to make clear claims about whether CI is a safe and effective way to manage it. [ 69 ]


The data for cochlear implant outcomes in older adults differs. A 2016 research study found that age at implantation was highly correlated with post-operative speech understanding performance for various test measures. In this study, people who were implanted at age 65 or older performed significantly worse on speech perception testing in quiet and in noisy conditions compared to younger CI users. [ 70 ]  Other studies have shown different outcomes, with some reporting that adults implanted at the age of 65 and older showed audiological and speech discrimination outcomes similar to younger adults. [ 71 ]  While cochlear implants demonstrate substantial benefit across all age groups, results will depend on cognitive factors that are ultimately highly age dependent. However, studies have documented the benefit of cochlear implants in octogenarians. [ 72 ] [ 73 ]


The effects of aging on central auditory processing abilities are thought to play an important role in impacting an individual's speech perception with a cochlear implant. The Lancet reported that untreated hearing loss in adults is the number one modifiable risk factor for dementia. [ 74 ]  In 2017, a study also reported that adults using a cochlear implant had significantly improved cognitive outcomes including working memory, reaction time, and cognitive flexibility compared to people who were waiting to receive a cochlear implant. [ 75 ]


Prolonged duration of deafness is another factor that is thought to have a negative impact on overall speech understanding outcomes for CI users. However, a study found no statistical difference in the speech understanding abilities of CI patients over 65 who had been hearing impaired for 30 years or more prior to implantation. [ 70 ]  In general, outcomes for CI patients are dependent upon the individual's level of motivation, expectations, exposure to speech stimuli and consistent participation in aural rehabilitation programs.


A 2016 systematic review of CI for people with  unilateral hearing loss  (UHL) found that of the studies conducted and published, none were randomized, only one evaluated a control group, and no study was blinded. After eliminating multiple uses of the same subjects, the authors found that 137 people with UHL had received a CI. [ 76 ]  While acknowledging the weakness of the data, the authors found that CI in people with UHL improves  sound localization  compared with other treatments in people who lost hearing after they learned to speak; in the one study that examined this, CI did improve sound localization in people with UHL who lost hearing before learning to speak. [ 76 ]  It appeared to improve  speech perception  and to reduce  tinnitus . [ 76 ]


In terms of quality of life, several studies have shown that cochlear implants are beneficial in many aspects of quality of life, including communication improvements and positive effects on social, emotional, psychological and physical well-being. A 2017 narrative review also concluded that the quality of life scores of children using cochlear implants were comparable to those of children without hearing loss. Studies involving adults of all ages reported significant improvement in QoL after implantation when compared to adults with  hearing aids . This was often independent of audiological performance. [ 77 ]


As of October 2010, [update]  approximately 188,000 individuals had been fitted with cochlear implants. [ 78 ]  As of December 2012, [update]  the same publication cited approximately 324,000 cochlear implant devices having been surgically implanted. In the U.S., roughly 58,000 devices were implanted in adults and 38,000 in children. [ 23 ]  As of 2016, [update]  the Ear Foundation in the United Kingdom, estimates the number of cochlear implant recipients in the world to be about 600,000. [ 79 ]  The American Cochlear Implant Alliance estimates that 217,000 people received CIs in the United States through the end of 2019. [ 80 ]


Cochlear implantation includes the medical device as well as related services and procedures including pre-operative testing, the surgery, and aftercare that includes audiology and speech language pathology services. These are provided over time by a team of clinicians with specialized training. All of these services, as well as the cochlear implant device and related peripherals, are part of the medical intervention and are typically covered by health insurance in the United States and many areas of the world. These medical services and procedures include candidacy evaluation, hospital services inclusive of supplies and medications used during surgery, surgeon and other physicians such as anesthesiologists, the cochlear implant device and system kit, and programming and (re)habilitation following the surgery. [ citation needed ]  In many countries around the world, the cost of cochlear implantation and aftercare is covered by health insurance. [ 81 ] [ 82 ]  However, financial factors impact the evaluation selection process. Children with public health insurance or no health insurance are less likely to receive the implant before 2 years old. [ 83 ]


In the US, as cochlear implants have become more commonplace and accepted as a valuable and cost effective health intervention, insurance coverage has expanded to include private insurance,  Medicare ,  Tricare , the VA System, other federal health plans, and  Medicaid . In September 2022 the  Centers for Medicare & Medicaid Services  expanded coverage of cochlear implants for appropriate candidates under Medicare. Candidates must demonstrate limited benefit with appropriately fit hearing aids but with criteria now defined by test scores of less than or equal to 60% correct in the best-aided listening condition on recorded tests of open-set sentence recognition. [ 84 ]  Just as there is with any medical procedure, there are typically co-pays which vary depending upon the insurance plan. [ 81 ] [ 82 ]


In the  United Kingdom , the  NHS  covers cochlear implants in full, as does Medicare in  Australia , and the Department of Health [ 85 ]  in  Ireland , Seguridad Social in  Spain , Sistema Sanitario Nazionale in  Italy , Sécurité Sociale in France [ 86 ]  and  Israel , and the Ministry of Health or  ACC  (depending on the cause of deafness) in  New Zealand . In  Germany  and  Austria , the cost is covered by most health insurance organizations. [ 87 ] [ 88 ]


6.1% of the world population live with hearing loss, and it is predicted that by 2050, more than 900 million people around the globe will have a disabling hearing loss. [ 89 ]  According to a WHO report, unaddressed hearing loss costs the world 980 billion dollars annually. Particularly hard hit are the healthcare and educational sectors, as well as societal costs. 53% of these costs are attributable to low- and middle-income countries. [ 90 ]


The WHO reports that cochlear implants have been shown to be a cost-effective way to mitigate the challenges of hearing loss. In a low-to-middle-income setting, every dollar invested in unilateral cochlear implants has a return on investment of 1.46 dollars. This rises to a return on investment of 4.09 dollars in an upper-middle-income setting. A study in Colombia assessed the lifetime investments made in 68 children who received cochlear implants at an early age. Taking into account the cost of the device and any other medical costs, follow-up, speech therapy, batteries and travel, each child required an average investment of US$99 000 over the course of their life (assuming a life span of 78 years for women and 72 years for men). The study concluded that for every dollar invested in rehabilitation of a child with a cochlear implant, there was a return on investment of US$2.07. [ 90 ]


As of 2021, four cochlear implant devices approved for use in the United States are manufactured by  Cochlear Limited , the  Advanced Bionics  division of  Sonova ,  MED-EL , and  Oticon Medical . [ 91 ] [ 92 ]


In Europe, Africa, Asia, South America, and Canada, an additional device manufactured by  Neurelec  (later acquired by Oticon Medical) was available. A device made by  Nurotron  (China) was also available in some parts of the world. Each manufacturer has adapted some of the successful innovations of the other companies to its own devices. There is no consensus that any one of these implants is superior to the others. Users of all devices report a wide range of performance after implantation. [ citation needed ]


Much of the strongest objection to cochlear implants has come from within the  deaf community , some of whom are pre-lingually deaf people whose first language is a  sign language . Some in the deaf community call cochlear implants  audist  and an affront to their culture, which, as they view it, is a minority threatened by the hearing majority. [ 93 ]  This is an old problem for the deaf community, going back as far as the 18th century with the argument of  manualism vs. oralism . This is consistent with medicalisation and the standardisation of the "normal" body in the 19th century when differences between normal and abnormal began to be debated. [ 94 ]  It is important to consider the sociocultural context, particularly in regards to the deaf community, which has its own unique language and culture. [ 95 ]  This accounts for the cochlear implant being seen as an affront to their culture, as many do not believe that deafness is something that needs to be cured. However, it has also been argued that this does not necessarily have to be the case: the cochlear implant can act as a tool deaf people can use to access the "hearing world" without losing their deaf identity. [ 95 ]


Cochlear implants for congenitally deaf children are most effective when implanted at a young age. [ 96 ]  Children who have had confirmed severe hearing loss can receive the implant as young as 9 months old. [ 97 ]  Evidence shows that deaf children of deaf parents (or with fluent signers as daily caregivers) learn signed language as effectively as hearing peers. Some deaf-community advocates recommend that all deaf children should learn sign language from birth, [ 98 ]  but more than 90% of deaf children are born to hearing parents. Since it takes years to become fluent in sign language, deaf children who grow up without amplification such as hearing aids or cochlear implants will not have daily access to fluent language models in households without fluent signers.


Critics of cochlear implants from deaf cultures also assert that the cochlear implant and the subsequent therapy often become the focus of the child's identity at the expense of language acquisition and ease of communication in sign language and deaf identity. They believe that measuring a child's success only by their mastery of speech will lead to a poor self-image as "disabled" (because the implants do not produce normal hearing) rather than having the healthy self-concept of a proudly deaf person. [ 99 ]  However, these assertions are not supported by research. The first children to receive cochlear implants as infants are only in their 20s (as of 2020), and anecdotal evidence points to a high level of satisfaction in this cohort, most of whom don't consider their deafness their primary identity. [ 55 ] [ 56 ] [ 100 ]


Children with cochlear implants are most likely to be educated with listening and spoken language, without  sign language  and are often not educated with other deaf children who use sign language. [ 101 ]  Cochlear implants have been one of the technological and social factors implicated in the decline of sign languages in the developed world. [ 102 ]  Some Deaf activists have labeled the widespread implantation of children as a  cultural genocide . [ 103 ]


As the trend for cochlear implants in children grows, deaf-community advocates have tried to counter the "either or" formulation of  oralism  vs.  manualism  with a "both and" or "bilingual-bicultural" [ 104 ]  approach; some schools are now successfully integrating cochlear implants with sign language in their educational programs. [ 105 ]  However, there is disagreement among researchers about the effectiveness of methods using both sign and speech as compared to sign or speech alone. [ 106 ] [ 107 ]


Another point of controversy made by advocates are that there are racial disparities in the cochlear implantation evaluation process. Data taken from 2010-2020 at one academic tertiary care institution showed that 68.5% of patients referred for evaluation were White, 18.5% were Black, and 12.3% were Asian, however the institution's main service area was 46.9% White, 42.3% Black, and 7.7% Asian. It was also shown that the Black patients who were referred for evaluation to receive the implants had greater hearing loss compared to White patients who were also referred. Based on this study, it is shown that Black patients receive cochlear implants at a disproportionately lower rate than White patients. [ 108 ]


Biderman, Beverly.   Wired for Sound: A Journey into Hearing Rev. 2016  Briar Hill Publishing


Craniofacial surgery  is a surgical  subspecialty  that deals with  congenital  and acquired  deformities  of the  head ,  skull ,  face ,  neck ,  jaws  and associated structures. Although craniofacial treatment often involves manipulation of bone, craniofacial surgery is not tissue-specific; craniofacial  surgeons  deal with bone, skin, nerve, muscle, teeth, and other related anatomy. [ 1 ] [ 2 ]


Defects typically treated by craniofacial surgeons include  craniosynostosis  (isolated and syndromic), rare  craniofacial clefts , acute and chronic sequelae of facial fractures,  cleft lip and palate , micrognathia,  Treacher Collins Syndrome ,  Apert's Syndrome ,  Crouzon's Syndrome , Craniofacial microsomia, microtia and other congenital ear anomalies, and many others. Training in craniofacial surgery requires completion of a Craniofacial surgery fellowship. Such fellowships are available to individuals who have completed residency in  oral and maxillofacial surgery ,  plastic  and  reconstructive surgery , or  ear, nose, and throat surgery . Those who have completed residency in oral and maxillofacial surgery may be either single degree or dual-degree surgeons with no differences. There is no specific board for craniofacial surgery. In the US, cleft and craniofacial centers are found in many major academic centers.


The bones of the human skull are joined by cranial  sutures  (see figure 1). The anterior fontanelle is where the metopic, sagittal and coronal sutures meet. Normally the sutures gradually fuse within the first few years after birth. In infants where one or more of the sutures fuses too early the growth of the skull is restricted, resulting in compensation mechanisms which cause irregular growth patterns. Growth in the skull is perpendicular to the sutures. When a suture fuses too early, the growth perpendicular to that suture will be restricted, and the bone growth near the other sutures will be stimulated, causing an abnormal head shape. The expanding brain is the main stimulus for the rapid growth of the skull in the first years of life. Inhibited growth potential of the skull can restrict the volume, needed by the brain. In cases in which the compensation does not effectively provide enough space for the growing brain,  craniosynostosis  results in increased intracranial pressure. [ 3 ]


Craniosynostosis is called simple when one suture is involved, and complex when two or more sutures are involved. It can occur as part of a syndrome or as an isolated defect (nonsyndromic). [ 4 ]


In scaphocephaly, the sagittal suture is prematurely fused. The sagittal suture runs from the front to the back of the head. The shape of this deformity is a long narrow head, formed like a boat (Greek  skaphe , "light boat or skiff"). The compensatory head-growth forward at the coronal suture gives a prominent forehead, frontal bossing and a prominent back of the head, called coning. [ 5 ]  The incidence of scaphocephaly is 2.8 per 10,000 births in the Netherlands; therefore, it is the most common form of craniosynostosis. [ 6 ] [ 7 ]


In trigonocephaly, the metopic suture is prematurely fused. The metopic suture is situated in the medial line of the forehead. Premature fusion of this suture causes the forehead to become pointed, giving the head a triangular shape when viewed from above (Greek  trigono , "triangle"). The incidence of trigonocephaly is 1 - 1.9 per 10,000 births in the Netherlands. [ 6 ]


In plagiocephaly, one of the coronal sutures is prematurely fused. The coronal sutures run over the top of the head, just in front of the ears. The shape of this deformity is an asymmetrical distortion (flattening of one side of the head) as you can see in figure 2. The incidence is 1 in 10,000 births. [ 6 ] [ 8 ]


In brachycephaly, both of the coronal sutures are prematurely fused. The shape of this deformity is a wide and high head. The incidence at birth is 1/20,000. [ 9 ]


Craniofacial surgery and follow-up care are usually conducted by a multidisclinary team of doctors, surgeons, nurses, and various therapists. [ 10 ]  As of 2016, there is a new multidisciplinary care team of Neuroplastic Surgeons working with Neurosurgeons to prevent and/or correct neurosurgical-related deformities and to maximize outcomes in adult patients.


In cases where the forehead is involved (trigonocephaly and plagiocephaly), a technique called fronto-supraorbital advancement is used to correct the shape of the head. The procedure is performed at a young age in order to provide the brain with enough space to grow and prevent further abnormal growth of the skull. Fronto-orbital advancement literally means moving the front of the skull including the eye sockets forward. A section of the skull, ranging from the coronal sutures to the eye sockets is cut loose in order to correct the shape of the skull. The incision is cut in a zigzag shape from ear to ear so that the hair will cover the scar and make it less visible. The incision is made to the bone only, leaving the underlying meninges intact. The top half of the eye sockets is cut loose. Once the eye socket section has been cut loose, a vertical incision is made in the midline, and the whole section of the eye socket is bent outwards in order to correct the pointed shape of the forehead. Because the section is now too wide, a wedge needs to be cut on either side to allow the section to fit into the skull. Figure 4 shows the sections that are loosened and adjusted, and Figure 3 shows the location of the vertical incision (arrow A) and the two wedges (arrow B). [ citation needed ]


In scaphocephaly, the sagittal suture is prematurely fused, preventing the skull from growing perpendicular to the suture. Thus, the head becomes very narrow and long. If a scaphocephaly is diagnosed within 4 to 5 months after birth, it can be corrected with a relatively simple procedure whereby the sagittal suture is surgically reopened. Once the suture has been opened the bone segments will be able to grow again, and the head can regain its normal shape. This operation is only performed on patients younger than five months old with a scaphocephaly. This is due to the fact that the bone segments only have the ability to adapt so severely when the operation is performed at this young age. A scaphocephaly that is diagnosed and treated later in life requires a more extensive secondary operation than one that is treated before five months. [ citation needed ]


A major focus in craniosynostosis reconstruction is maintaining normalized aesthetics of temporal region, and avoiding temporal hollowing. Despite using overcorrection methods, autologous fat transfer, and bone grafts to prevent temporal hollowing, up to 50% of patients still experience post-operative depression in the temporal fossa.


Cranioplasty, or skull reconstruction, is the main concentration of a new field for adult neurosurgical patients known as Neuroplastic Surgery. There are now several centers around the world, including the United States and Israel. The first center of Neuroplastic Surgery was started at Johns Hopkins by Dr. Chad Gordon and the Department of Neurosurgery, which is where this new craniofacial subspecialty was born ( c.  2016 ). [ 11 ]


Some of the surgical complications in craniofacial surgery may include Death, Shock, Haemorrhage, visual loss, Intracranial collection of air/fluid, Epileptic seizures, Unexpected respiratory complications, etc. [ 12 ]


In  mammalian  anatomy, the  cribriform plate  ( Latin  for  lit.   sieve -shaped ),  horizontal lamina  or  lamina cribrosa  is part of the  ethmoid bone . It is received into the  ethmoidal notch  of the  frontal bone  and roofs in the  nasal cavities . It supports the  olfactory bulb , and is perforated by  olfactory foramina  for the passage of the  olfactory nerves  to the roof of the  nasal cavity  to convey smell to the brain. The foramina at the  medial  part of the groove allow the passage of the nerves to the upper part of the  nasal septum  while the foramina at the lateral part transmit the nerves to the  superior nasal concha .


A fractured cribriform plate can result in  olfactory dysfunction ,  septal hematoma ,  cerebrospinal fluid rhinorrhoea  (CSF rhinorrhoea), and possibly infection which can lead to  meningitis . CSF rhinorrhoea (clear fluid leaking from the nose) is very serious and considered a  medical emergency . Aging can cause the openings in the cribriform plate to close, pinching olfactory nerve fibers. A reduction in olfactory receptors, loss of blood flow, and thick nasal mucus can also cause an impaired sense of smell. [ 1 ]


The cribriform plate is part of the  ethmoid bone , which has a low density, and is spongy. [ 2 ]  It is narrow, with deep grooves supporting the  olfactory bulb .


Its anterior border, short and thick, articulates with the  frontal bone . It has two small projecting alae (wings), which are received into corresponding depressions in the frontal bone to complete the  foramen cecum .


Its sides are smooth, and sometimes bulging due to the presence of a small  air sinus  in the interior.


The  crista galli  projects upwards from the middle line of the cribriform plate. The long thin posterior border of the crista galli serves for the attachment of the  falx cerebri . On either side of the crista galli, the cribriform plate is narrow and deeply grooved. At the front part of the cribriform plate, on either side of the crista galli, is a small fissure that is occupied by a process of  dura mater .


Lateral to this fissure is a notch or foramen which transmits the  nasociliary nerve ; from this notch a groove extends backward to the anterior ethmoidal foramen.


The cribriform plate is formed from the fetal age to the end of the first year, completing ossification. Deriving from the nasal capsule, formation begins specifically during the 5th week of gestation. Ossification begins at its most anterior part and proceeds in a posterior manner. The position also shifts from vertical during the 1st postnatal month to horizontal at the age of 6 months.


The Keros classification is a method of classifying the depth of the olfactory fossa.


The depth of the olfactory fossa is determined by the height of the lateral lamella of the cribriform plate.  Keros  in 1962, classified the depth into three categories. [ 3 ]


The cribriform plate is perforated by  olfactory foramina , which allow for the passage of the  olfactory nerves  to the roof of the  nasal cavity . [ 4 ]  This conveys information from smell receptors to the  brain . The foramina at the  medial  part of the groove allow the passage of the nerves to the upper part of the  nasal septum  while the foramina at the lateral part transmit the nerves to the  superior nasal concha .


A fractured cribriform plate (anterior skull trauma) can result in leaking of  cerebrospinal fluid  into the nose and  loss of sense of smell . The tiny apertures of the plate transmitting the olfactory nerve become the route of ascent for a pathogen,  Naegleria fowleri . This  amoeba  tends to destroy the olfactory bulb and the adjacent inferior surface of the frontal lobe of the brain. This surface initially becomes the site of proliferation of the  trophozoites  of  Naegleria fowleri  and their subsequent spread to the rest of the brain and CSF. Because of its initial involvement and trophozoite presence in early phases of  Naegleria fowleri  infection, flushing of this region with saline using a device, to obtain  Naegleria fowleri  for diagnostic PCR and microscopic viewing, has been proposed for patients affected by  naegleriasis , by (Baig AM., et al.) in a recent publication. [ 5 ]  Researchers have suggested the same route to administer drugs at an early phase of infection by using a "Transcribrial Device" [ 6 ]  that has been proposed to kill this pathogen at the place of its maximum proliferation. In 2017 the inventor of this device suggested that after slight modifications this method could be effective in delivery of stem cells to the brain as well. [ 7 ]  A recent Australian study has shown that the bacterium causing the tropical disease  melioidosis ,  Burkholderia pseudomallei , can also invade the brain via the olfactory nerve within 24 h by traversing the cribriform plate. [ 8 ]


The cribriform plate is named after its resemblance to a sieve (from Latin  cribrum , "sieve" + -form). [ 2 ]  It is also known as the horizontal lamina, and the lamina cribrosa.


The cribriform plate is found in every  mammal  that has been studied. [ 9 ]  It serves the same function of allowing passage of the  olfactory nerves . [ 9 ]


This article incorporates text in the  public domain  from  page 153  of the 20th edition of   Gray's Anatomy   (1918)


Croup  ( / k r uː p /   KROOP ), also known as  croupy cough , is a type of  respiratory infection  that is usually caused by a  virus . [ 2 ]  The infection leads to swelling inside the  trachea , which interferes with normal breathing and produces the classic symptoms of "barking/brassy"  cough , inspiratory  stridor  and a  hoarse voice . [ 2 ]   Fever  and  runny nose  may also be present. [ 2 ]  These symptoms may be mild, moderate, or severe. [ 3 ]  Often it starts or is worse at night and normally lasts one to two days. [ 6 ] [ 2 ] [ 3 ]


Croup can be caused by a number of viruses including  parainfluenza  and  influenza virus . [ 2 ]  Rarely is it due to a  bacterial infection . [ 5 ]  Croup is typically diagnosed based on signs and symptoms after potentially more severe causes, such as  epiglottitis  or an  airway foreign body , have been ruled out. [ 4 ]  Further investigations, such as blood tests,  X-rays  and cultures, are usually not needed. [ 4 ]


Many cases of croup are preventable by  immunization  for  influenza  and  diphtheria . [ 5 ]  Most cases of croup are mild and the patient can be treated at home with supportive care. Croup is usually treated with a single dose of  steroids  by mouth. [ 2 ] [ 7 ]  In more severe cases inhaled  epinephrine  may also be used. [ 2 ] [ 8 ]  Hospitalization is required in one to five percent of cases. [ 9 ]


Croup is a relatively common condition that affects about 15% of children at some point. [ 4 ]  It most commonly occurs between six months and five years of age but may rarely be seen in children as old as fifteen. [ 3 ] [ 4 ] [ 9 ]  It is slightly more common in males than females. [ 9 ]  It occurs most often in autumn. [ 9 ]  Before  vaccination , croup was frequently caused by  diphtheria  and was often fatal. [ 5 ] [ 10 ]  This cause is now very rare in the  Western world  due to the success of the  diphtheria vaccine . [ 11 ]


Croup is characterized by a "barking"  cough ,  stridor ,  hoarseness , and  difficult breathing  which usually worsens at night. [ 2 ]  The "barking" cough is often described as resembling the call of a  sea lion . [ 5 ]   The stridor is worsened by agitation or  crying , and if it can be heard at rest, it may indicate critical narrowing of the airways. As croup worsens, stridor may decrease considerably. [ 2 ]


Other symptoms include  fever ,  coryza  (symptoms typical of the  common cold ), and indrawing of the  chest wall –known as  Hoover's sign . [ 2 ] [ 12 ]   Drooling  or a very sick appearance can indicate other medical conditions, such as  epiglottitis  or  tracheitis . [ 12 ]


Croup is usually deemed to be due to a viral infection. [ 2 ] [ 4 ]  Others use the term more broadly, to include acute laryngotracheitis ( laryngitis  and  tracheitis  together), spasmodic croup, laryngeal diphtheria, bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis. The first two conditions involve a viral infection and are generally milder with respect to symptomatology; the last four are due to bacterial infection and are usually of greater severity. [ 5 ]


Viral croup or acute laryngotracheitis is most commonly caused by  parainfluenza virus  (a member of the  paramyxovirus  family), primarily types 1 and 2, in 75% of cases. [ 3 ]  Other viral causes include  influenza  A and B,  measles ,  adenovirus  and  respiratory syncytial virus  (RSV). [ 5 ]  Spasmodic croup is caused by the same group of viruses as acute laryngotracheitis, but lacks the usual signs of infection (such as fever, sore throat, and increased  white blood cell count ). [ 5 ]   Treatment, and response to treatment, are also similar. [ 3 ]


Croup caused by a bacterial infection is rare. [ 13 ]  Bacterial croup may be divided into laryngeal diphtheria, bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis. [ 5 ]   Laryngeal diphtheria is due to  Corynebacterium diphtheriae  while bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis are usually due to a primary viral infection with secondary bacterial growth.  The most common cocci implicated are  Staphylococcus aureus  and  Streptococcus pneumoniae , while the most common bacteria are  Haemophilus influenzae , and  Moraxella catarrhalis . [ 5 ]


The viral infection that causes croup leads to swelling of the  larynx ,  trachea , and large  bronchi [ 4 ]  due to infiltration of  white blood cells  (especially  histiocytes ,  lymphocytes ,  plasma cells , and  neutrophils ). [ 5 ]  Swelling produces airway obstruction which, when significant, leads to dramatically increased work of breathing and the characteristic turbulent, noisy airflow known as  stridor . [ 4 ]


Croup is typically diagnosed based on signs and symptoms. [ 4 ]  The first step is to exclude other obstructive conditions of the upper airway, especially  epiglottitis , an airway  foreign body ,  subglottic stenosis ,  angioedema ,  retropharyngeal abscess , and  bacterial tracheitis . [ 4 ] [ 5 ]


A frontal  X-ray  of the neck is not routinely performed, [ 4 ]  but if it is done, it may show a characteristic narrowing of the trachea, called the  steeple sign , because of the subglottic stenosis, which resembles a  steeple  in shape.  The steeple sign is suggestive of the diagnosis, but is absent in half of cases. [ 12 ]


Other investigations (such as  blood tests  and  viral culture ) are discouraged, as they may cause unnecessary agitation and thus worsen the stress on the compromised airway. [ 4 ]  While viral cultures, obtained via  nasopharyngeal  aspiration, can be used to confirm the exact cause, these are usually restricted to research settings. [ 2 ]  Bacterial infection should be considered if a person does not improve with standard treatment, at which point further investigations may be indicated. [ 5 ]


The most commonly used system for classifying the severity of croup is the Westley score. It is primarily used for research purposes rather than in clinical practice. [ 5 ]  It is the sum of points assigned for five factors: level of consciousness, cyanosis, stridor, air entry, and retractions. [ 5 ]  The points given for each factor is listed in the adjacent table, and the final score ranges from 0 to 17. [ 14 ]


85% of children presenting to the emergency department have mild disease; severe croup is rare (<1%). [ 3 ]


Croup is contagious during the first few days of the infection. [ 13 ]  Basic hygiene including hand washing can prevent transmission. [ 13 ]  There are no vaccines that have been developed to prevent croup, [ 13 ]  however, many cases of croup have been prevented by  immunization  for  influenza  and  diphtheria . [ 5 ]  At one time, croup referred to a diphtherial disease, but with vaccination, diphtheria is now rare in the developed world. [ 5 ]


Most children with croup have mild symptoms and supportive care at home is effective. [ 13 ]  For children with moderate to severe croup, treatment with corticosteroids and nebulized epinephrine may be suggested. Steroids are given routinely, with  epinephrine  used in severe cases. [ 4 ]  Children with  oxygen saturation  less than 92% should receive oxygen, [ 5 ]  and those with severe croup may be hospitalized for observation. [ 12 ]  In very rare severe cases of croup that result in respiratory failure, emergency intubation and ventilation may be required. [ 15 ]  With treatment, less than 0.2% of children require  endotracheal intubation . [ 14 ]  Since croup is usually a viral disease,  antibiotics  are not used unless secondary bacterial infection is suspected. [ 2 ]  The use of  cough medicines , which usually contain  dextromethorphan  or  guaifenesin , are also discouraged. [ 2 ]


Supportive care for children with croup includes resting and keeping the child hydrated. [ 13 ]  Infections that are mild are suggested to be treated at home. Croup is contagious so washing hands is important. [ 13 ]  Children with croup should generally be kept as calm as possible. [ 4 ]  Over the counter medications for pain and fever may be helpful to keep the child comfortable. [ 13 ]  There is some evidence that cool or warm mist may be helpful, however, the effectiveness of this approach is not clear. [ 4 ] [ 5 ] [ 13 ]  If the child is showing signs of distress while breathing ( inspiratory stridor , working hard to breathe, blue (or blue-ish) coloured lips, or decrease in the level of  alertness ), immediate medical evaluation by a doctor is required. [ 13 ]


Corticosteroids , such as  dexamethasone  and  budesonide , have been shown to improve outcomes in children with all severities of croup, however, the benefits may be delayed. [ 7 ]  Significant relief may be obtained as early as two hours after administration. [ 7 ]  While effective when given  by injection , or by inhalation, giving the medication by mouth is preferred. [ 4 ]  A single dose is usually all that is required, and is generally considered to be quite safe. [ 4 ]  Dexamethasone at doses of  0.15, 0.3 and 0.6 mg/kg appear to be all equally effective. [ 16 ]


Moderate to severe croup (for example, in the case of severe stridor) may be improved temporarily with  nebulized   epinephrine . [ 4 ]  While epinephrine typically produces a reduction in croup severity within 10–30 minutes, the benefits are short-lived and last for only about 2 hours. [ 2 ] [ 4 ]  If the condition remains improved for 2–4 hours after treatment and no other complications arise, the child is typically discharged from the hospital. [ 2 ] [ 4 ]  Epinephrine treatment is associated with potential adverse effects (usually related to the dose of epinephrine) including  tachycardia ,  arrhythmias , and  hypertension . [ 15 ]


More severe cases of croup may require treatment with oxygen. If oxygen is needed, "blow-by" administration (holding an oxygen source near the child's face) is recommended, as it causes less agitation than use of a  mask . [ 5 ]


While other treatments for croup have been studied, none has sufficient evidence to support its use.  There is tentative evidence that breathing  heliox  (a mixture of  helium  and  oxygen ) to decrease the work of breathing is useful in those with severe disease, however, there is uncertainty in the effectiveness and the potential adverse effects and/or side effects are not well known. [ 15 ]   In cases of possible secondary bacterial infection, the antibiotics  vancomycin  and  cefotaxime  are recommended. [ 5 ]  In severe cases associated with  influenza A  or  B  infections, the  antiviral   neuraminidase inhibitors  may be administered. [ 5 ]


Viral croup is usually a  self-limiting  disease, [ 2 ]  with half of cases resolving in a day and 80% of cases in two days. [ 6 ]  It can very rarely result in death from  respiratory failure  and/or  cardiac arrest . [ 2 ]   Symptoms usually improve within two days, but may last for up to seven days. [ 3 ]  Other uncommon complications include  bacterial tracheitis ,  pneumonia , and  pulmonary edema . [ 3 ]


Croup affects about 15% of children, and usually presents between the ages of 6 months and 5–6 years. [ 4 ] [ 5 ]  It accounts for about 5% of hospital admissions in this population. [ 3 ]  In rare cases, it may occur in children as young as 3 months and as old as 15 years. [ 3 ]  Males are affected 50% more frequently than are females, and there is an increased  prevalence  in autumn. [ 5 ]


The word  croup  comes from the  Early Modern English  verb  croup , meaning "to cry hoarsely." The noun describing the disease originated in southeastern Scotland and became widespread after  Edinburgh  physician  Francis Home  published the 1765 treatise  An Inquiry into the Nature, Cause, and Cure of the Croup . [ 17 ] [ 18 ]


Diphtheritic croup  has been known since the time of  Homer 's  ancient Greece , and it was not until 1826 that viral croup was differentiated from croup due to  diphtheria  by  Bretonneau . [ 11 ] [ 19 ]  Viral croup was then called "faux-croup" by the French and often called "false croup" in English, [ 20 ] [ 21 ]  as "croup" or "true croup" then most often referred to the disease caused by the  diphtheria bacterium . [ 22 ] [ 23 ]  False croup has also been known as pseudo croup or spasmodic croup. [ 24 ]  Croup due to diphtheria has become nearly unknown in affluent countries in modern times due to the advent of effective  immunization . [ 11 ] [ 25 ]


One famous fatality of croup was  Napoleon 's designated heir,  Napoléon Charles Bonaparte . His death in  1807  left Napoleon without an heir and contributed to his decision to divorce from his wife, the Empress  Josephine de Beauharnais . [ 26 ]


A  cystic hygroma  is a form of  lymphatic malformation . It is an abnormal growth that usually appears on a baby's neck or head. It consists of one or more  cysts  and tends to grow larger over time. The disorder usually develops while the fetus is still in the uterus, but can also appear after birth.


Also known as  cystic lymphangioma  and  macrocystic lymphatic malformation , the growth is often a  congenital   lymphatic   lesion  of many small cavities (multiloculated) that can arise anywhere, but is classically found in the left  posterior triangle  of the  neck  and armpits. The malformation contains large  cyst -like cavities containing  lymph , a watery fluid that circulates throughout the  lymphatic system . Microscopically, cystic hygroma consists of multiple  locules  filled with lymph. Deep locules are quite big, but they decrease in size towards the surface.


Cystic hygromas are  benign , but can be  disfiguring . It is a condition which usually affects children; very rarely it can be present in adulthood. [ 2 ]


Currently, the medical field prefers to use the term  lymphatic malformation , because the term cystic hygroma means water tumor. [ 3 ]  Lymphatic malformation is more commonly used now because it is a  sponge -like collection of abnormal growth that contains clear lymphatic fluid. The fluid collects within the cysts or channels, usually in the soft tissue. Cystic hygromas occur when the  lymphatic vessels  that make up the lymphatic system are not formed properly. The two types of lymphatic malformations are macrocystic  (large cysts) and microcystic (small cysts) lymphatic malformations. A person may have only one kind of the malformation or can have a mixture of both macro- and microcysts.


Cystic hygroma can be associated with a  nuchal   lymphangioma  or a  fetal hydrops . [ 4 ]  Additionally, it can be associated with  Down syndrome ,  Turner syndrome , [ 5 ]  or  Noonan syndrome . If it is diagnosed in the third trimester, then chances of association with Down syndrome are increased, but if diagnosed in the second trimester, then it is associated with Turner syndrome.


A lethal version [ 6 ]  of this condition exists, known as  Cowchock–Wapner–Kurtz syndrome , that, in addition to cystic hygroma, includes  cleft palate  and  lymphedema , a condition of localized  edema  and tissue swelling caused by a compromised lymphatic system. [ 7 ]


Cystic hygromas are increasingly diagnosed by  prenatal   ultrasonography . A common sign is a neck growth. It may be found at birth, or discovered later in an infant after an  upper respiratory tract infection . [ 8 ]  Cystic hygromas can grow very large and may affect breathing and swallowing. Some symptoms may include a mass or lump in the mouth, neck, cheek, or tongue. It feels like a large, fluid-filled sac. In addition, cystic hygromas can be found in other body parts, such as the arms, chest, legs, groin, and buttocks. Cystic hygromas are also often seen in Turner's syndrome, although a patient who does not have the syndrome can present with this condition.


Lymphatic malformations may be detected in the human fetus by ultrasound if they are of sufficient size. Detection of a cystic malformation may prompt further investigation, such as  amniocentesis , to evaluate for genetic abnormalities in the fetus. Lymphatic malformations may be discovered postnatally or in older children/adults, and most commonly present as a mass or as an  incidental finding  during  medical imaging .


Verification of the diagnosis may require more testing, as multiple cystic masses can arise in children. [ 9 ]  Imaging, such as ultrasound or MRI, may provide more information as to the size and extent of the lesion.


A baby with a prenatally diagnosed cystic hygroma should be delivered in a major medical center equipped to deal with neonatal complications, such as a  neonatal intensive care unit . An  obstetrician  usually decides the method of delivery. If the cystic hygroma is large, a  cesarean section  may be performed. After birth, infants with a persistent cystic hygroma must be monitored for airway obstruction. A thin needle may be used to reduce the volume of the cystic hygroma to prevent facial deformities and airway obstruction. Close observation of the baby by a  neonatologist  after birth is recommended. If resolution of the cystic hygroma does not occur before birth, a  pediatric surgeon  should be consulted. [ 10 ]


Cystic hygromas that develop in the third trimester, after 30 weeks' gestation, or in the  postnatal period  are usually not associated with  chromosome abnormalities . A chance exists of recurrence after  surgical  removal of the cystic hygroma. The chance depends on the extent of the cystic hygroma and whether its wall was completely removed. [ 10 ]


Treatments for removal of cystic hygroma are surgery or  sclerosing agents , which include:


The  deep temporal space   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 deep to the  temporalis muscle


The inferior portion of the deep temporal space is also termed the  infratemporal space . The deep temporal space is one of the four  compartments  of the  masticator space , along with the  pterygomandibular space , the  submasseteric space  and the  superficial temporal space . [ 1 ]  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. [ 1 ] [ 2 ] [ 3 ] [ 4 ]


The boundaries of the deep temporal space are:


Superior :


Superior and Inferior temporal lines


Inferior :


Infratemporal crest and Zygomatic arch


The communications of the deep temporal space are:


The contents of the deep temporal space are:


Temporalis muscle


Identification of a  hearing loss  is usually conducted by a general practitioner  medical doctor ,  otolaryngologist , certified and licensed  audiologist , school or industrial  audiometrist , or other audiometric technician. Diagnosis of the cause of a hearing loss is carried out by a specialist physician (audiovestibular physician) or  otorhinolaryngologist .


Difference between subjective and objective hearing test .


Subjective:


Objective:


A case history (usually a written form, with questionnaire) can provide valuable information about the context of the hearing loss, and indicate what kind of diagnostic procedures to employ. Case history will include such items as:


In case of infection or inflammation, blood or other body fluids may be submitted for laboratory analysis.


Hearing loss is generally measured by playing generated or recorded sounds, and determining whether the person can hear them. Hearing sensitivity varies according to the  frequency  of sounds. To take this into account, hearing sensitivity can be measured for a range of frequencies and plotted on an  audiogram .


Other method for quantifying hearing loss is a  hearing test  using a mobile application or  hearing aid application , which includes a  hearing test . [ 1 ] [ 2 ]  Hearing diagnosis using mobile application is similar to the  audiometry  procedure. As a result of  hearing test ,  hearing thresholds  at different frequencies ( audiogram ) are determined. Despite the errors in the measurements, application can help to diagnose hearing loss. [ 1 ]   Audiogram , obtained using mobile application, can be used to adjust  hearing aid application . [ 2 ]


An alternative approach to assessing hearing impairment is through the utilization of a speech-in-noise test. This evaluation method assesses an individual's ability to comprehend speech amidst background noise. Individuals with hearing loss typically experience difficulty in understanding speech, particularly in environments with high levels of noise. This is especially true for people who have a sensorineural loss – which is by far the most common type of hearing loss. As such, speech-in-noise tests can provide valuable information about a person's hearing ability, and can be used to detect the presence of a sensorineural hearing loss. A recently developed digit-triple speech-in-noise test may be a more efficient screening test. [ 3 ]


Otoacoustic emissions test is an objective hearing test that may be administered to toddlers and children too young to cooperate in a conventional hearing test. The test is also useful in older children and adults and is an important measure in diagnosing auditory neuropathy described above.


Auditory brainstem response testing is an electrophysiological test used to test for hearing deficits caused by pathology within the ear, the cochlear nerve and also within the brainstem. This test can be used to identify delay in the conduction of neural impulses due to tumours or inflammation but can also be an objective test of hearing thresholds. Other electrophysiological tests, such as cortical evoked responses, can look at the hearing pathway up to the level of the auditory cortex.


MRI and CT scans can be useful to identify the pathology of many causes of hearing loss. They are only needed in selected cases. [ vague ]


Hearing loss is categorized by type, severity, and configuration. Furthermore, a hearing loss may exist in only one ear (unilateral) or in both ears (bilateral).  Hearing loss can be temporary or permanent, sudden or progressive.


The severity of a hearing loss is ranked according to ranges of nominal thresholds in which a sound must be so it can be detected by an individual. It is measured in  decibels  of hearing loss, or dB HL. The measurement of hearing loss in an individual is conducted over several  frequencies , mostly 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. The hearing loss of the individual is the average of the hearing loss values over the different frequencies. Hearing loss can be ranked differently according to different organisations; and so, in different countries different systems are in use.


Hearing loss may be ranked as slight, mild, moderate, moderately severe, severe or profound as defined below: [ medical citation needed ]


The 'Audiometric Classifications of Hearing Impairment' according to the International Bureau Audiophonology (BIAP) in Belgium is as follows: [ 5 ]


Hearing loss may affect one or both ears. If both ears are affected, then one ear may be more affected than the other.  Thus it is possible, for example, to have normal hearing in one ear and none at all in the other, or to have mild hearing loss in one ear and moderate hearing loss in the other.


For certain legal purposes such as insurance claims, hearing loss is described in terms of percentages. Given that hearing loss can vary by frequency and that audiograms are plotted with a logarithmic scale, the idea of a percentage of hearing loss is somewhat arbitrary, but where decibels of loss are converted via a legally recognized formula, it is possible to calculate a standardized "percentage of hearing loss", which is suitable for legal purposes only.


There are three main types of hearing loss,  conductive hearing loss ,  sensorineural hearing loss . Combinations of conductive and sensorineural hearing losses are called a mixed hearing loss. [ 4 ]  An additional problem which is increasingly recognised is  auditory processing disorder  which is not a hearing loss as such but a difficulty perceiving sound.


Conductive hearing loss is present when the sound is not reaching the inner ear, the  cochlea . This can be due to external ear canal malformation, dysfunction of the eardrum or malfunction of the bones of the middle ear. The eardrum may show defects from small to total resulting in hearing loss of different degree.  Scar tissue  after ear infections may also make the eardrum dysfunction as well as when it is retracted and adherent to the medial part of the middle ear.


Dysfunction of the three small bones of the  middle ear  – malleus, incus, and stapes – may cause conductive hearing loss. The mobility of the  ossicles  may be impaired for different reasons including a boney disorder of the ossicles called  otosclerosis  and disruption of the ossicular chain due to trauma, infection or  ankylosis  may also cause hearing loss.


Sensorineural hearing loss is one caused by dysfunction of the inner ear, the cochlea or the nerve that transmits the impulses from the cochlea to the hearing centre in the brain. The most common reason for sensorineural hearing loss is damage to the  hair cells  in the cochlea. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has impaired hearing. [ 6 ]


Damage to the brain can lead to a central deafness. The peripheral ear and the auditory nerve may function well but the central connections are damaged by tumour, trauma or other disease and the patient is unable to process speech information.


Mixed hearing loss is a combination of conductive and sensorineural hearing loss. Chronic ear infection (a fairly common diagnosis) can cause a defective  ear drum  or middle-ear ossicle damages, or both.  In addition to the conductive loss, a sensory component may be present.


This is not an actual hearing loss but gives rise to significant difficulties in hearing. One kind of auditory processing disorder is  King-Kopetzky syndrome , which is characterized by an inability to process out background noise in noisy environments despite normal performance on traditional hearing tests. An  auditory processing disorders  is sometimes linked to language disorders in persons of all ages.


The shape of an audiogram shows the relative configuration of the hearing loss, such as a  Carhart notch  for otosclerosis, 'noise' notch for noise-induced damage, high frequency rolloff for presbycusis, or a flat audiogram for conductive hearing loss. In conjunction with speech audiometry, it may indicate central auditory processing disorder, or the presence of a  schwannoma  or other tumor. There are four general configurations of hearing loss:


People with  unilateral hearing loss  or single-sided deafness (SSD) have difficulty in:


In quiet conditions, speech discrimination is approximately the same for normal hearing and those with unilateral deafness; however, in noisy environments speech discrimination varies individually and ranges from mild to severe.


One reason for the hearing problems these patients often experience is due to the  head shadow effect . Newborn children with no hearing on one side but one normal ear could still have problems. [ 7 ]  Speech development could be delayed and difficulties to concentrate in school are common. More children with unilateral hearing loss have to repeat classes than their peers. Taking part in social activities could be a problem. Early aiding is therefore of utmost importance. [ 8 ] [ 9 ]


The  digastric muscle  (also  digastricus ) (named  digastric  as it has two 'bellies') is a bilaterally paired  suprahyoid muscle  located under the  jaw . Its posterior belly is attached to the  mastoid notch of temporal bone , and its anterior belly is attached to the  digastric fossa of mandible ; the two bellies are united by an intermediate tendon which is held in a loop that attaches to the hyoid bone. The anterior belly is innervated via the  mandibular nerve (cranial nerve V) , and the posterior belly is innervated via the  facial nerve (cranial nerve VII) . It may act to depress the mandible or elevate the hyoid bone.


The term "digastric muscle" refers to this specific muscle even though there are other muscles in the body to feature two bellies. [ citation needed ]


The digastric muscle consists of two muscular bellies united by an intermediate tendon. The posterior belly is longer than the anterior belly. The two bellies of the digastric muscle have different  embryological  origins - the anterior belly is derived from the first brachial arch and the posterior belly from the second brachial arch - and consequently differ in their innervation (the former being innervated via CN V and the latter via CN VII). [ 1 ]


The posterior belly attaches at the  mastoid notch of the temporal bone [ 1 ]  (which is located upon the inferior surface of the skull, medial to the  mastoid process  of the  temporal bone  - between the mastoid process and the  styloid process  of the temporal bone). [ citation needed ]


It extends anteroinferiorly from its osseous attachment toward the intermediate tendon. [ 1 ]


The anterior belly attaches at the  digastric fossa of mandible  (situated at the base of the mandible near the midline). [ 1 ]


It extends inferoposteriorly from its origin toward the intermediate tendon. [ 1 ]


The two bellies meet at the intermediate  tendon  which perforates the  stylohyoideus  muscle. The tendon is embraced by a fibrous sling which attaches the body and  greater cornu  of  hyoid bone . The tendon occasionally features a  synovial sheath . [ 1 ]


The anterior belly receives motor innervation from the  mylohyoid nerve  (a branch of the  inferior alveolar nerve , which is in turn a branch of the  mandibular division of the trigeminal nerve (CN V 3 ) ). [ 1 ]


The posterior belly is supplied by the  digastric branch of facial nerve . [ citation needed ]


The posterior belly is situated posterior to the parotid gland [ 2 ]  and the facial nerve. [ citation needed ]


The digastric muscle divides the  anterior triangle of the neck  into four smaller triangles: the  submandibular triangle (digastric triangle) , the  carotid triangle , the  submental triangle (suprahyoid triangle) , and the  inferior carotid triangle (muscular triangle) . [ citation needed ]


The intermediate tendon may be absent. The posterior belly may arise partly (by an supplemental strip of muscle) or entirely from the styloid process of the temporal bone. [ 1 ]  It may be connected by a  muscle slip  to the middle or inferior constrictor. [ citation needed ]


The anterior belly may be double, or extra slips from this belly may pass to the jaw or mylohyoideus or decussate with a similar slip on opposite side. It may be absent and posterior belly inserted into the middle of the jaw or hyoid bone. [ citation needed ]  It may fuse with the  mylohyoid muscle . [ 1 ]


The tendon may pass in front, more rarely behind the stylohyoideus. The mentohyoideus muscle passes from the body of hyoid bone to chin. [ citation needed ]


The muscle depresses the mandible, and may elevate the hyoid bone. [ 1 ]


It depresses the  mandible  when the hyoid bone is held in place (by the  infrahyoid muscles ). [ citation needed ]


The digastric muscle is involved in any complex jaw action such as speaking, swallowing, chewing, and breathing. [ citation needed ]  The posterior belly is particularly functionally involved in swallowing and chewing. [ 1 ]


The digastric muscles are present in a variety of animals, specific attachment sites may vary. For example, in the  orangutan , the posterior digastric attaches to the  mandible  rather than the hyoid. [ citation needed ]


This article incorporates text in the  public domain  from  page 391  of the 20th edition of   Gray's Anatomy   (1918)


A  direct acoustic cochlear implant  - also  DACI  - is an  acoustic   implant  which converts  sound  in  mechanical  vibrations that stimulate directly the  perilymph  inside the  cochlea . The hearing function of the external and middle  ear  is being taken over by a little  motor  of a  cochlear implant , directly stimulating the cochlea. With a DACI, people with no or almost no residual hearing but with a still functioning inner ear, can again perceive speech, sounds and music.
DACI is an official product category, as indicated by the nomenclature of  GMDN . [ 1 ]


A DACI tries to provide an answer for people with hearing problems for which no solution exists today. People with some problems at the level of the cochlea can be helped with a  hearing aid . A hearing aid will absorb the incoming sound from a microphone, and offer enhanced through the natural way. For larger reinforcements, this may cause problems with  feedback  and  distortion . A hearing aid also simply provides more loudness, no more resolution. Users will view this often as, "all sounds louder, but I understand nothing more than before."
Once a hearing aid offers no solution anymore, one can switch to a  cochlear implant . A Cochlear implant captures the sound and sends it electrically, through the cochlea, to the auditory nerve. In this way, completely deaf patients can perceive sounds again.
However, As soon as there are problems not only at the level of the cochlea, but also in the middle ear (the so-called  conductive  losses), then there are more efficient ways to get sound to the partially functioning cochlea.
The most obvious solution is a  BAHA , which brings the sound to the cochlea via bone conduction.
However, patients who have both problems with the cochlea, as with the middle ear (i.e. patients with mixed losses), none of the above solutions is ideal.
To this end, the direct acoustic cochlear implant was developed. A DACI brings the sound directly to the cochlea, and provides the most natural way of sound amplification.


The first DACI was implanted in Hannover. In Belgium, the first DACI was implanted at the Catholic University Hospital of Leuven. [ 2 ]   In the Netherlands, the Radboud clinic in Nijmegen was the first while in Poland it was first implanted at the Institute of Physiology and Pathology of Hearing in Warsaw. [ 3 ]


The  dorsal nasal artery  is an  artery  of the  face . [ citation needed ]  It is one of the two terminal branches of the  ophthalmic artery . It contributes arterial supply to the  lacrimal sac , and outer surface of the nose.


The dorsal nasal artery is one of the two terminal branches of the  ophthalmic artery  (the other being the  supratrochlear artery ). [ 1 ]  It arises in the superomedial orbit. [ 2 ]


It passes anteriorly [ citation needed ]  to exit the orbit between the  trochlea  (superiorly [ citation needed ] ), the  medial palpebral ligament  (inferiorly [ citation needed ] ). [ 1 ]  It gives a branch to the  lacrimal sac  before bifurcating into two branches: one branch anastomoses with the terminal (angular) part of the  facial artery [ 1 ]  and is important for the blood supply of the  face ; [ citation needed ]  the other travels along the dorsum of the nose to supply the outer surface of the nose, and forms anastomoses with its contralateral fellow, and with the  lateral nasal branch  of the  facial artery . [ 1 ]


The dorsal nasal artery contributes arterial supply to the  lacrimal sac , [ 1 ] [ 3 ]  and the outer surface of the nose. [ 1 ]


In around 20% of individuals, it also supplies the tip of the nose. [ 3 ]


This  cardiovascular system  article is a  stub . You can help Wikipedia by  expanding it .


Dysgeusia , also known as  parageusia , is a distortion of the sense of taste. Dysgeusia is also often associated with  ageusia , which is the complete lack of taste, and  hypogeusia , which is a decrease in taste sensitivity. [ 1 ]  An alteration in taste or smell may be a secondary process in various disease states, or it may be the primary  symptom . The distortion in the sense of taste is the only symptom, and  diagnosis  is usually complicated since the sense of taste is tied together with other  sensory systems . Common causes of dysgeusia include  chemotherapy , asthma treatment with  albuterol , and  zinc deficiency . Liver disease,  hypothyroidism , and rarely, certain types of  seizures  can also lead to dysgeusia. Different drugs can also be responsible for altering taste and resulting in dysgeusia. Due to the variety of causes of dysgeusia, there are many possible treatments that are effective in alleviating or terminating the symptoms. These include artificial saliva, pilocarpine, zinc supplementation, alterations in drug therapy, and alpha lipoic acid.


The alterations in the sense of  taste , usually a metallic taste, and sometimes  smell  are the only symptoms. [ 2 ]


A major cause of dysgeusia is  chemotherapy  for cancer. Chemotherapy often induces damage to the oral cavity, resulting in  oral mucositis , oral infection, and salivary gland dysfunction. Oral mucositis consists of  inflammation  of the mouth, along with sores and  ulcers  in the tissues. [ 3 ]  Healthy individuals normally have a diverse range of microbial  organisms  residing in their oral cavities; however, chemotherapy can permit these typically non- pathogenic  agents to cause serious infection, which may result in a decrease in  saliva . In addition, patients who undergo  radiation therapy  also lose salivary tissues. [ 4 ]  Saliva is an important component of the taste mechanism. Saliva both interacts with and protects the taste receptors in the mouth. [ 5 ]  Saliva mediates sour and sweet tastes through bicarbonate ions and glutamate, respectively. [ 6 ]  The salt taste is induced when sodium chloride levels surpass the concentration in the saliva. [ 6 ]  It has been reported that 50% of chemotherapy patients have had either dysgeusia or another form of taste impairment. [ 3 ]  Examples of chemotherapy treatments that can lead to dysgeusia are  cyclophosphamide ,  cisplatin ,  vismodegib , [ 7 ]  and  etoposide . [ 3 ]  The exact mechanism of chemotherapy-induced dysgeusia is unknown. [ 3 ]


Distortions in the  taste buds  may give rise to dysgeusia. In a study conducted by Masahide Yasuda and Hitoshi Tomita from Nihon University of Japan, it has been observed that patients with this taste disorder have fewer  microvilli  than normal. In addition, the  nucleus  and  cytoplasm  of the taste bud cells have been reduced. Based on their findings, dysgeusia results from loss of microvilli and the reduction of Type III intracellular vesicles, all of which could potentially interfere with the gustatory pathway.  Radiation to head and neck also results in direct destruction of taste buds, apart from effects of altered salivary output. [ 8 ]


Another primary cause of dysgeusia is  zinc  deficiency. While the exact role of zinc in dysgeusia is unknown, it has been cited that zinc is partly responsible for the repair and production of taste buds. Zinc somehow directly or indirectly interacts with  carbonic anhydrase VI , influencing the concentration of gustin, which is linked to the production of taste buds. [ 9 ]  It has also been reported that patients treated with zinc experience an elevation in  calcium  concentration in the saliva. [ 9 ]  In order to work properly, taste buds rely on calcium receptors. [ 10 ]  Zinc "is an important cofactor for  alkaline phosphatase , the most abundant  enzyme  in taste bud membranes; it is also a component of a parotid salivary protein important to the development and maintenance of normal taste buds". [ 10 ]


Miraculin  Found in miracle berries, sweetens nonsweet food and beverages.


Gymnema sylvestre  Blocks the ability to taste sweetness.


There are also a wide variety of drugs that can trigger dysgeusia, including  zopiclone , [ 11 ]  H 1 - antihistamines , such as  azelastine  and  emedastine . [ 12 ]  Approximately 250 drugs affect taste, including  Paxlovid , a drug used to treat  COVID-19 . [ 13 ]  Some describe so-called "Paxlovid mouth" as like a "mouthful of dirty pennies and rotten soymilk", according to the  Wall Street Journal . [ 14 ]


The  sodium  channels linked to taste receptors can be inhibited by  amiloride , and the creation of new taste buds and saliva can be impeded by  antiproliferative  drugs. [ 13 ]  Saliva can have traces of the drug, giving rise to a metallic flavor in the mouth; examples include  lithium carbonate  and  tetracyclines . [ 13 ]  Drugs containing  sulfhydryl  groups, including  penicillamine  and  captopril , may react with zinc and cause deficiency. [ 10 ]   Metronidazole  and  chlorhexidine  have been found to interact with metal ions that associate with the  cell membrane . [ 15 ]  Drugs that act by blocking the  renin–angiotensin–aldosterone system , for example by  antagonizing the angiotensin II receptor  (as  eprosartan  does), have been linked to dysgeusia. [ 16 ]  There are few case reports claiming calcium channel blockers like  Amlodipine  also cause dysgeusia by blocking calcium sensitive taste buds. [ 17 ]


Changes in hormone levels during pregnancy, such as estrogen, can affect the sense of taste. [ 18 ]  A study found that 93 percent of pregnant women reported some change in taste during pregnancy. [ 18 ]


Xerostomia , also known as dry mouth syndrome, can precipitate dysgeusia because normal salivary flow and concentration are necessary for taste. Injury to the  glossopharyngeal nerve  can result in dysgeusia. In addition, damage done to the  pons ,  thalamus , and  midbrain , all of which compose the gustatory pathway, can be potential factors. [ 19 ]  In a case study, 22% of patients who were experiencing a bladder obstruction were also experiencing dysgeusia. Dysgeusia was eliminated in 100% of these patients once the obstruction was removed. [ 19 ]  Although it is uncertain what the relationship between bladder relief and dysgeusia entails, it has been observed that the areas responsible for  urinary system  and taste in the pons and  cerebral cortex  in the brain are close in proximity. [ 19 ]


Dysgeusia can be a symptom of  head and neck cancer . In this case it often present together with having dry mouth. [ 20 ]


Dysgeusia often occurs for unknown reasons. A wide range of miscellaneous factors may contribute to this taste disorder, such as  gastric reflux ,  lead poisoning , and  diabetes mellitus . [ 21 ]  A minority of  pine nuts  can apparently cause taste disturbances, for reasons which are not entirely proven. Certain pesticides can have damaging effects on the taste buds and nerves in the mouth. These  pesticides  include  organochloride  compounds and  carbamate  pesticides. Damage to the  peripheral nerves , along with injury to the  chorda tympani  branch of the facial nerve, also cause dysgeusia. [ 21 ]  A surgical risk for  laryngoscopy  and  tonsillectomy  include dysgeusia. [ 21 ]  Patients with  burning mouth syndrome , primarily  menopausal  women, often have dysgeusia as well. [ 22 ]


The sense of taste is based on the detection of chemicals by specialized taste cells in the mouth. The mouth, throat, larynx, and esophagus all have  taste buds , which are replaced every ten days. Each taste bud contains receptor cells. [ 21 ]  Afferent nerves make contact with the receptor cells at the base of the taste bud. [ 23 ]  A single taste bud is innervated by several afferent nerves, while a single efferent fiber innervates several taste buds. [ 24 ]   Fungiform papillae  are present on the anterior portion of the tongue while  circumvallate papillae  and  foliate papillae  are found on the posterior portion of the tongue. The  salivary glands  are responsible for keeping the taste buds moist with saliva. [ 25 ]


A single taste bud is composed of four types of cells, and each taste bud has between 30 and 80 cells. Type I cells are thinly shaped, usually in the periphery of other cells. They also contain high amounts of  chromatin . Type II cells have prominent  nuclei  and nucleoli with much less chromatin than Type I cells. Type III cells have multiple  mitochondria  and large  vesicles . Type I, II, and III cells also contain  synapses . Type IV cells are normally rooted at the posterior end of the taste bud. Every cell in the taste bud forms  microvilli  at the ends. [ 8 ]


In general,  gustatory  disorders are challenging to diagnose and evaluate. Because gustatory functions are tied to the sense of  smell , the  somatosensory system , and the perception of  pain  (such as in tasting spicy foods), it is difficult to examine sensations mediated through an individual system. [ 26 ]  In addition, gustatory dysfunction is rare when compared to  olfactory  disorders. [ 27 ]


Diagnosis of dysgeusia begins with the patient being questioned about  salivation , swallowing, chewing, oral pain, previous  ear infections  (possibly indicated by hearing or balance problems),  oral hygiene , and stomach problems. [ 28 ]  The initial history assessment also considers the possibility of accompanying diseases such as  diabetes mellitus ,  hypothyroidism , or  cancer . [ 28 ]  A clinical examination is conducted and includes an inspection of the tongue and the oral cavity. Furthermore, the  ear canal  is inspected, as lesions of the  chorda tympani  have a predilection for this site. [ 28 ]


In order to further classify the extent of dysgeusia and clinically measure the sense of taste, gustatory testing may be performed. Gustatory testing is performed either as a whole-mouth procedure or as a regional test. In both techniques, natural or electrical stimuli can be used. In regional testing, 20 to 50 μL of liquid stimulus is presented to the  anterior  and  posterior  tongue using a pipette, soaked filter-paper disks, or cotton swabs. [ 27 ]  In whole mouth testing, small quantities (2-10 mL) of solution are administered, and the patient is asked to swish the solution around in the mouth. [ 27 ]


Threshold  tests for  sucrose  (sweet),  citric acid  (sour),  sodium chloride  (salty), and  quinine  or  caffeine  (bitter) are frequently performed with natural stimuli. One of the most frequently used techniques is the "three-drop test". [ 29 ]  In this test, three drops of liquid are presented to the subject. One of the drops is of the taste stimulus, and the other two drops are pure water. [ 29 ]  Threshold is defined as the concentration at which the patient identifies the taste correctly three times in a row. [ 29 ]


Suprathreshold tests, which provide intensities of taste stimuli above threshold levels, are used to assess the patient's ability to differentiate between different intensities of taste and to estimate the magnitude of suprathreshold loss of taste. From these tests, ratings of pleasantness can be obtained using either the direct scaling or magnitude matching method and may be of value in the diagnosis of dysgeusia. Direct scaling tests show the ability to discriminate among different intensities of stimuli and whether a stimulus of one quality (sweet) is stronger or weaker than a stimulus of another quality (sour). [ 30 ]  Direct scaling cannot be used to determine if a taste stimulus is being perceived at abnormal levels. In this case, magnitude matching is used, in which a patient is asked to rate the intensities of taste stimuli and stimuli of another  sensory system , such as the loudness of a tone, on a similar scale. [ 30 ]  For example, the Connecticut Chemosensory Clinical Research Center asks patients to rate the intensities of NaCl, sucrose, citric acid and quinine-HCl stimuli, and the loudness of 1000 Hz tones. [ 30 ]


Other tests include identification or discrimination of common taste substances.  Topical anesthesia  of the tongue has been reported to be of use in the diagnosis of dysgeusia as well, since it has been shown to relieve the symptoms of dysgeusia temporarily. [ 27 ]  In addition to techniques based on the administration of chemicals to the tongue,  electrogustometry  is frequently used. It is based on the induction of gustatory sensations by means of an anodal electrical  direct current . Patients usually report sour or metallic sensations similar to those associated with touching both poles of a live battery to the tongue. [ 31 ]  Although electrogustometry is widely used, there seems to be a poor correlation between electrically and chemically induced sensations. [ 32 ]


Certain diagnostic tools can also be used to help determine the extent of dysgeusia.  Electrophysiological  tests and simple reflex tests may be applied to identify abnormalities in the  nerve -to- brainstem  pathways. For example, the  blink reflex  may be used to evaluate the integrity of the  trigeminal nerve – pontine brainstem – facial nerve  pathway, which may play a role in gustatory function. [ 33 ]


Structural imaging is routinely used to investigate  lesions  in the taste pathway.  Magnetic resonance imaging  allows direct visualization of the  cranial nerves . [ 34 ]  Furthermore, it provides significant information about the type and cause of a lesion. [ 34 ]  Analysis of  mucosal   blood flow  in the oral cavity in combination with the assessment of  autonomous   cardiovascular  factors appears to be useful in the diagnosis of  autonomic nervous system  disorders in  burning mouth syndrome  and in patients with inborn disorders, both of which are associated with gustatory dysfunction. [ 35 ]   Cell cultures  may also be used. [ 36 ]


In addition, the analysis of  saliva  should be performed, as it constitutes the environment of  taste receptors , including transport of tastes to the receptor and protection of the taste receptor. [ 37 ]  Typical clinical investigations involve sialometry and sialochemistry. [ 37 ]  Studies have shown that  electron micrographs  of taste receptors obtained from saliva samples indicate  pathological  changes in the taste buds of patients with dysgeusia and other gustatory disorders. [ 38 ]


Because medications have been linked to approximately 22% to 28% of all cases of dysgeusia, researching a treatment for this particular cause has been important. [ 39 ]   Xerostomia , or a decrease in saliva flow, can be a side effect of many drugs, which, in turn, can lead to the development of taste disturbances such as dysgeusia. [ 39 ]  Patients can lessen the effects of xerostomia with breath mints, sugarless gum, or lozenges; or physicians can increase saliva flow with artificial saliva or oral  pilocarpine . [ 39 ]  Artificial saliva mimics the characteristics of natural saliva by lubricating and protecting the mouth, but does not provide any digestive or enzymatic benefits. [ 40 ]  Pilocarpine is a  cholinergic  drug, meaning it has the same effects as the  neurotransmitter   acetylcholine . Acetylcholine has the function of stimulating the  salivary glands  to actively produce saliva. [ 41 ]  The increase in saliva flow is effective in improving the movement of tastants to the  taste buds . [ 39 ]


Approximately one half of drug-related taste distortions are caused by a  zinc deficiency . [ 39 ]  Many medications are known to  chelate , or bind,  zinc , preventing the element from functioning properly. [ 39 ]  Due to the causal relationship of insufficient zinc levels to taste disorders, research has been conducted to test the efficacy of zinc supplementation as a possible treatment for dysgeusia. In a randomized clinical trial, fifty patients with  idiopathic  dysgeusia were given either zinc or a lactose  placebo . [ 9 ]  The patients prescribed the zinc reported experiencing improved taste function and less severe symptoms compared to the control group, suggesting that zinc may be a beneficial treatment. [ 9 ]  The efficacy of zinc, however, has been ambiguous in the past. In a second study, 94% of patients who were provided with zinc supplementation did not experience any improvement in their condition. [ 39 ]  This ambiguity is most likely due to small sample sizes and the wide range of causes of dysgeusia. [ 9 ]  A recommended daily oral dose of 25–100 mg, as  zinc gluconate , appears to be an effective treatment for taste dysfunction provided that there are low levels of zinc in the  blood serum . [ 42 ]  There is not a sufficient amount of evidence to determine whether or not zinc supplementation is able to treat dysgeusia when low zinc concentrations are not detected in the blood. [ 42 ]


A Cochrane Review in 2017 assessed the effects of different interventions for the management of taste disturbances. There was very low-quality evidence to support the role of zinc supplementation in the improvement of taste acuity and taste discrimination in patients with zinc deficiency or idiopathic taste disorders. Further research is required to improve the quality of evidence for zinc supplementation as an effective intervention for the management of dysgeusia. [ 43 ]


It has been reported that approximately 68% of cancer patients undergoing  chemotherapy  experience disturbances in sensory perception such as dysgeusia. [ 44 ]  In a pilot study involving twelve lung cancer patients, chemotherapy drugs were infused with zinc in order to test its potential as a treatment. [ 45 ]  The results indicated that, after two weeks, no taste disturbances were reported by the patients who received the zinc-supplemented treatment while most of the patients in the control group who did not receive the zinc reported taste alterations. [ 45 ]  A multi-institutional study involving a larger sample size of 169 patients, however, indicated that zinc-infused chemotherapy did not have an effect on the development of taste disorders in cancer patients. [ 44 ]  An excess amount of zinc in the body can have negative effects on the  immune system , and physicians must use caution when administering zinc to  immunocompromised  cancer patients. [ 44 ]  Because taste disorders can have detrimental effects on a patient's quality of life, more research needs to be conducted concerning possible treatments such as zinc supplementation. [ 46 ]


The effects of drug-related dysgeusia can often be reversed by stopping the patient's regimen of the taste altering medication. [ 47 ]  In one case, a forty-eight-year-old woman who had  hypertension  was being treated with  valsartan . [ 48 ]  Due to this drug's inability to treat her condition, she began taking a regimen of  eprosartan , an  angiotensin II receptor antagonist . [ 48 ]  Within three weeks, she began experiencing a metallic taste and a burning sensation in her mouth that ceased when she stopped taking the medication. [ 48 ]  When she began taking eprosartan on a second occasion, her dysgeusia returned. [ 48 ]  In a second case, a fifty-nine-year-old man was prescribed  amlodipine  in order to treat his hypertension. [ 49 ]  After eight years of taking the drug, he developed a loss of taste sensation and numbness in his tongue. [ 49 ]  When he ran out of his medication, he decided not to obtain a refill and stopped taking amlodipine. [ 49 ]  Following this self-removal, he reported experiencing a return of his taste sensation. [ 49 ]  Once he refilled his prescription and began taking amlodipine a second time, his taste disturbance reoccurred. [ 49 ]  These two cases suggest that there is an association between these drugs and taste disorders. This link is supported by the "de-challenge" and "re-challenge" that took place in both instances. [ 49 ]  It appears that drug-induced dysgeusia can be alleviated by reducing the drug's dose or by substituting a second drug from the same class. [ 39 ]


Alpha lipoic acid  (ALA) is an  antioxidant  that is made naturally by human cells. [ 50 ]  It can also be administered in capsules or can be found in foods such as red meat, organ meats, and yeast. [ 50 ]  Like other antioxidants, it functions by ridding the body of harmful  free radicals  that can cause damage to tissues and organs. [ 50 ]  It has an important role in the  Krebs cycle  as a  coenzyme  leading to the production of antioxidants, intracellular  glutathione , and nerve-growth factors. [ 51 ]  Animal research has also uncovered the ability of ALA to improve  nerve conduction velocity . [ 51 ]  Because flavors are perceived by differences in  electric potential  through specific nerves innervating the tongue, idiopathic dysgeusia may be a form of a  neuropathy . [ 51 ]  ALA has proven to be an effective treatment for  burning mouth syndrome , spurring studies in its potential to treat dysgeusia. [ 51 ]  In a study of forty-four patients diagnosed with the disorder, one half was treated with the drug for two months, while the other half, the control group, was given a placebo for two months, followed by a two-month treatment of ALA. [ 51 ]  The results showed that 91% of the group initially treated with ALA reported an improvement in their condition compared to only 36% of the control group. [ 51 ]  After the control group was treated with ALA, 72% reported an improvement. [ 51 ]  This study suggests that ALA may be a potential treatment for patients, and supports that full double blind randomized studies should be performed. [ 51 ]


In addition to the aforementioned treatments, there are also many management approaches that can alleviate the symptoms of dysgeusia. These include using non-metallic silverware, avoiding metallic- or bitter-tasting foods, increasing the consumption of foods high in protein, flavoring foods with spices and seasonings, serving foods cold in order to reduce any unpleasant taste or odor, frequently brushing one's teeth and utilizing mouthwash, or using  sialogogues  such as sugar-free gum or sour-tasting drops that stimulate the production of saliva. [ 44 ]  When taste is impeded, the food experience can also be improved through means other than taste, such as texture, aroma, temperature, and color. [ 47 ]


People with dysgeusia are also forced to manage the impact that the disorder has on their quality of life. An altered sense of taste has effects on food choice and intake, and can lead to  weight loss ,  malnutrition , impaired immunity, and a decline in health. [ 47 ]  Patients diagnosed with dysgeusia must use caution when adding sugar and salt to food, and must be sure not to overcompensate for their lack of taste with excess amounts. [ 47 ]  Since the elderly are often on multiple medications, they are at risk for taste disturbances, increasing the chances of developing  depression , loss of appetite, and extreme weight loss. [ 52 ]  This is cause for evaluation and management of their dysgeusia. In patients undergoing chemotherapy, taste distortions can often be severe, and make compliance with cancer treatment difficult. [ 45 ]  Other problems that may arise include  anorexia , and behavioral changes that can be misinterpreted as psychiatric delusions regarding food. [ 53 ]  Symptoms including  paranoia ,  amnesia , cerebellar malfunction, and  lethargy  can also manifest when undergoing  histidine  treatment. [ 53 ]


Every year, more than 200,000 individuals see their physicians concerning  chemosensory  problems, and many more taste disturbances are never reported. [ 54 ]  Due to the large number of persons affected by taste disorders, basic and clinical research are both receiving support at different institutions and chemosensory research centers across the United States. [ 54 ]  These taste and smell clinics are focusing their research on better understanding the mechanisms involved in gustatory function and taste disorders such as dysgeusia. For example, the  National Institute on Deafness and Other Communication Disorders  is looking into the mechanisms underlying the key receptors on taste cells, and applying this knowledge to the future of medications and artificial food products. [ 54 ]  Meanwhile, the Taste and Smell Clinic at the  University of Connecticut Health Center  is integrating behavioral, neurophysiological, and genetic studies involving stimulus concentrations and intensities, in order to better understand taste function. [ 55 ]


Dysphagia  is difficulty in swallowing. [ 1 ] [ 2 ]  Although classified under " symptoms and signs " in  ICD-10 , [ 3 ]  in some contexts it is classified as a  condition  in its own right. [ 4 ] [ 5 ] [ 6 ]


It may be a sensation that suggests difficulty in the passage of solids or liquids from the mouth to the stomach, [ 7 ]  a lack of  pharyngeal  sensation or various other inadequacies of the swallowing mechanism. Dysphagia is distinguished from other symptoms including  odynophagia , which is defined as painful swallowing, [ 8 ]  and  globus , which is the sensation of a lump in the throat. A person can have dysphagia without odynophagia (dysfunction without pain), odynophagia without dysphagia (pain without dysfunction) or both together. A  psychogenic  dysphagia is known as  phagophobia . [ 9 ]


Dysphagia is classified into the following major types: [ 10 ]


Some patients have limited awareness of their dysphagia, so lack of the symptom does not exclude an underlying disease. [ 11 ]  When dysphagia goes undiagnosed or untreated, patients are at a high risk of  pulmonary aspiration  and subsequent  aspiration pneumonia  secondary to food or liquids going the wrong way into the lungs. Some people present with "silent aspiration" and do not cough or show outward signs of aspiration. Undiagnosed dysphagia can also result in dehydration, malnutrition, and kidney failure. [ 12 ]


Some signs and symptoms of oropharyngeal dysphagia include difficulty controlling food in the mouth, inability to control food or saliva in the mouth, difficulty initiating a swallow, coughing, choking, frequent  pneumonia , unexplained weight loss, gurgly or wet voice after swallowing, nasal regurgitation, and patient complaint of swallowing difficulty. [ 11 ]  When asked where the food is getting stuck, patients will often point to the cervical ( neck ) region as the site of the obstruction. The actual site of obstruction is always at or below the level at which the level of obstruction is perceived. [ citation needed ]


The most common symptom of esophageal dysphagia is the inability to swallow solid food, which the patient will describe as 'becoming stuck' or 'held up' before it either passes into the stomach or is regurgitated. Pain on swallowing or  odynophagia  is a distinctive symptom that can be highly indicative of  carcinoma , although it also has numerous other causes that are not related to cancer.  Achalasia  is a major exception to usual pattern of dysphagia in that swallowing of fluid tends to cause more difficulty than swallowing solids. In achalasia, there is idiopathic destruction of parasympathetic ganglia of the  Auerbach's (Myenteric) plexus  of the entire esophagus, which results in functional narrowing of the lower  esophagus , and peristaltic failure throughout its length. [ 13 ]


Complications of dysphagia may include  aspiration ,  pneumonia ,  dehydration , and weight loss. [ 14 ]


The following table enumerates possible causes of dysphagia:


Difficulty with or inability to swallow may be caused or exacerbated by usage of opiate and/or opioid drugs. [ 15 ]


All causes of dysphagia are considered as differential diagnoses. Some common ones are: [ 17 ]


Esophageal dysphagia is almost always caused by disease in or adjacent to the esophagus but occasionally the lesion is in the pharynx or stomach. In many of the pathological conditions causing dysphagia, the lumen becomes progressively narrowed and indistensible. Initially, only fibrous solids cause difficulty but later the problem can extend to all solids and later even to liquids. Patients with difficulty swallowing may benefit from  thickened fluids  if the person is more comfortable with those liquids, although, so far, there is no scientific study that proves that those thickened liquids are beneficial. [ 22 ]


Dysphagia may manifest as the result of  autonomic nervous system  pathologies including stroke [ 23 ]  and  ALS , [ 24 ]  or due to rapid iatrogenic correction of an electrolyte imbalance. [ 25 ]


In older adults,  presbyphagia  - the normal healthy changes in swallowing associated with age - should be considered as an alternative explanation for symptoms. [ 26 ]


There are many ways to treat dysphagia, such as swallowing therapy, dietary changes, feeding tubes, certain medications, and surgery. Treatment for dysphagia is managed by a group of specialists known as a multidisciplinary team. Members of the multidisciplinary team include: a speech language pathologist specializing in swallowing disorders (swallowing therapist), primary physician, gastroenterologist, nursing staff, respiratory therapist, dietitian, occupational therapist, physical therapist, pharmacist, and radiologist. [ 11 ]  The role of the members of the multidisciplinary team will differ depending on the type of swallowing disorder present. For example, the swallowing therapist will be directly involved in the treatment of a patient with  oropharyngeal dysphagia , while a gastroenterologist will be directly involved in the treatment of an esophageal disorder. [ citation needed ]


The implementation of a treatment strategy should be based on a thorough evaluation by the multidisciplinary team. Treatment strategies will differ on a patient to patient basis and should be structured to meet the specific needs of each individual patient. Treatment strategies are chosen based on a number of different factors including diagnosis, prognosis, reaction to compensatory strategies, severity of dysphagia, cognitive status, respiratory function, caregiver support, and patient motivation and interest. [ 11 ]


Adequate nutrition and hydration must be preserved at all times during dysphagia treatment. The overall goal of dysphagia therapy is to maintain or return the patient to, oral feeding. However, this must be done while ensuring adequate nutrition and hydration and a safe swallow (no aspiration of food into the lungs). [ 11 ]  If oral feeding results in increased mealtimes and increased effort during the swallow, resulting in not enough food being ingested to maintain weight, a supplementary nonoral feeding method of nutrition may be needed. In addition, if the patient aspirates food or liquid into the lungs despite the use of compensatory strategies, and is therefore unsafe for oral feeding, nonoral feeding may be needed. Nonoral feeding includes receiving nutrition through a method that bypasses the oropharyngeal swallowing mechanism including a nasogastric tube, gastrostomy, or jejunostomy. [ 11 ]  Some people with dysphagia, especially those nearing the  end of life , may choose to continue eating and drinking orally even when it has been deemed unsafe. This is known as "risk feeding". [ 27 ]


A 2018 Cochrane review found no certain evidence about the immediate and long-term effects of modifying the thickness of fluids for swallowing difficulties in people with dementia. [ 28 ]  While thickening fluids may have an immediate positive effect on swallowing and improving oral intake, the long-term impact on the health of the person with dementia should also be considered. [ 22 ]


Compensatory treatment procedures are designed to change the flow of the food/liquids and eliminate symptoms but do not directly change the physiology of the swallow. [ 11 ]


Therapeutic treatment procedures – designed to change and/or improve the physiology of the swallow. [ 11 ] [ 29 ]


Patients may need a combination of treatment procedures to maintain a safe and nutritionally adequate swallow. For example, postural strategies may be combined with swallowing maneuvers to allow the patient to swallow in a safe and efficient manner. [ citation needed ]


The most common interventions used for those with oropharyngeal dysphagia by speech language pathologists are rehabilitation of the swallow through oral motor exercises, texture modification of foods, thickening fluids and positioning changes during swallowing. [ 30 ]  The effectiveness of modifying food and fluid in preventing aspiration pneumonia has been questioned and these can be associated with poorer nutrition, hydration and quality of life. [ 31 ]  Also, there has been considerable variability in national approaches to describing different degrees of thickened fluids and food textures.  However, in 2015, the International Dysphagia Diet Standardisation Initiative (IDDSI) group produced an agreed IDDSI framework consisting of a continuum of 8 levels (0–7), where drinks are measured from Levels 0 – 4, while foods are measured from Levels 3 – 7. [ 32 ]   It is likely that this initiative, which has widespread support among dysphagia practitioners, will improve communication with carers and will lead to greater standardisation of modified diets [ citation needed ]


Swallowing disorders can occur in all age groups, resulting from congenital abnormalities, structural damage, and/or medical conditions. [ 11 ]  Swallowing problems are a common complaint among older individuals, and the  incidence  of dysphagia is higher in the elderly, [ 33 ] [ 34 ]  and in patients who have had strokes. [ 35 ]
Dysphagia affects about 3% of the population. [ 36 ]


The word "dysphagia" is derived from the  Greek   dys  meaning bad or disordered, and the root  phag-  meaning "eat". [ citation needed ]