Ear Anomalies and Hearing Loss

Common ear and hearing defects

The ear is formed from three parts:

• the external ear - pinna (auricle), external acoustic meatus and external layer of tympanic membrane
• the middle ear (three auditory ossicles connecting the internal layer of the tympanic membrane to the oval window of the internal ear)
• the internal ear (vestibulocochlear organ of semicircular canals for balance and cochlea for hearing)

Congenital hearing loss may be conductive, due to defects in the ossicles or tympanic membrane. Sensorineural loss arises due to problems with the cochlea (internal ear), auditory nerves or brain cortex. Central (sensory) hearing loss results from damage to the auditory nerve itself, or the brain pathways that lead to the nerve. Central hearing loss is rare in infants and children.

 

External ear (pinna or auricle)

Minor anomalies are common. There is a wide variation in size and shape of the external ear in the normal population. Minor variations may indicate chromosomal syndromes (eg trisomy 18 or 21) or maternal drug usage (eg isotretinoin).

Microtia is a small/malformed pinna, and anotia is the total absence of the pinna. These can occur as an isolated anomaly or with other anomalies, commonly facial clefts and cardiac defects. Microtia/anotia can cause conductive hearing loss if there is atresia of the external acoustic meatus (often genetic causes) or middle ear problems. The condition can be on one side or bilateral (10%). It can be associated with chromosomal syndromes, maternal drugs (eg thalidomide) and single gene conditions (Treacher Collins syndrome). Associations include advanced maternal age, low maternal education attainment, lack of folic acid, insulin dependent diabetes, high parity, high altitude areas, urban residence and male infant sex.

 

Middle ear

Congenital choleasteatoma is a keratin filled cyst found on the inside of a normal tympanic membrane.  It can cause conductive hearing loss. The treatment is surgical removal even if this impairs hearing as it is a recurrent destructive process within the middle ear.

 

Inner ear and hearing loss

Congenital anomalies of the inner ear can cause sensorineural hearing loss. Most of these are caused by abnormalities of the hair cells in the cochlea and are genetic in origin.

 

Embryology

Development starts early in the fourth week of gestation. The inner ear develops separately from that of the middle and inner ear.

 

Causes and risk factors

Ear defects and deafness are associated with a wider variety of genetic and environmental factors. More than 40 genes have been identified that cause deafness. This may be due to isolated gene defects or as part of a wider syndrome.

 

Syndromes

• Waardenburg syndrome – hypertrichosis of eyebrows meeting in midline, heterochromia of the irises (different colour eyes), white forelock
• Klippel Feil syndrome – short neck, low hairline at back, restricted mobility of the upper spine
• Alport syndrome – is usually inherited as an X linked dominant and affects boys more than girls. There is severe progressive glomerulonephritis. Deafness is also progressive and if not screened may not be apparent before 10 years of age.

 

Non syndromic causes

• In developed counties, 60-80% of cases of early-onset hearing loss are of genetic origin. Mutations in the gene encoding connexin 26 appear to be responsible for the majority of cases.This is found when the baby inherits a flawed copy of the gene that affects the protein Connexin 26 from both parents. Hearing loss is thought to be caused by the resulting change in potassium flow in the inner ear
• Maternal infections during pregnancy, particularly the first trimester can affect inner ear development and cause sensorineural hearing loss. Infections causing deafness include cytomegalovirus (CMV), toxoplasmosis and syphilis. Rubella infection in the seventh and eighth weeks of pregnancy can also affect the development of the cochlea and cause significant deafness. Fortunately congenital rubella remains extremely rare in Wales. However, there is concern that cases could increase as there has been a decline since 1998 in Measles Mumps Rubella (MMR) vaccination
• Ototoxic drugs Some drugs taken in pregnancy can affect hearing. These include the aminoglycosides (eg streptomycin) and quinine
• Alcohol. Sensorineural hearing loss can be part of the clinical picture of fetal alcohol syndrome
• Prematurity: About 5% of premature babies will have some degree of sensorineural hearing loss

 

Detection

Detection of external ear anomalies is made through physical examination.

Newborn neonatal screening for bilateral hearing loss was introduced in Wales in 2003. CARIS data show how the proportion of cases diagnosed in the first month of life has increased following introduction of the screening programme from 4% to 29% of cases of bilateral hearing loss.

 

 

 

 

 

Management

A key aim is early detection and management of hearing loss in order to try and maintain development of communication skills in affected babies and young children. This involves multi agency working in partnership with the child and family and includes:

• Family support and information
• Maximising hearing. For example through hearing aids, audio loops and radio aids; cochlear implants
• Communication support including:
  • Speech therapy to help children develop listening skills and speech
  • Lip reading/speech reading.
  • British Sign Language (BSL) and / or finger spelling
  • Pre-school and school support, including needs assessment and provision (Tidy, 2014 )

Treatment for external ear anomalies may not be required. For severe microtia or anotia, prostheses can be used from about the age of 3 years and surgery from age 7to8 years. Middle ear anomalies may also be amenable to surgical treatment, depending on the nature and extent of the defect.

 

Works cited

• Forfar and Arneil (1998) Textbook of Paediatrics, Churchill Livingstone
• Matsunaga, T. (2009). "Value of genetic testing in the otological approach for sensorineural hearing loss". The Keio journal of medicine58 (4): 216–222.
• Moore and Persaud (2003) Before We Are Born, Saunders
• Tidy, C. (2014 , 03 21). Deafness in Children. Retrieved from Patient.co.uk