Inner Ear Disorders and Sensorineural Hearing Loss (SNHL) - Vocabulary

These disorders result in inner ear problems (cochlear problems) and, therefore, pure-tone carbon: SENSORINEURAL HEARING LOSS (SNHL) due to damage to cochlear structures.
Organ of Corti is affected primarily at the basal turn; individual hair cells are severely damaged or missing.
Stria vascularis may become atrophied (wasted away/degenerated).
Tectorial membrane appears shriveled and rolled up.
Reissner’s membrane collapses to the point that it attaches to the basilar membrane.
These structural changes contribute to sensorineural hearing loss.
Disorders to be discussed include childhood diseases (viral infections) and other perinatal insults: Chicken Pox, Measles (rubella is not listed here but measles is), Mumps, Toxoplasmosis (parasitic infection), Meningitis (bacterial infection), Cytomegalovirus (CMV) (viral infection), Syphilis & Herpes (bacterial and viral infections), Rh factor incompatibility, and Anoxia.

All of these can cause sensorineural hearing loss (SNHL).
Degrees of loss can range from slight to profound.
All are caused by viruses (acquired postnatally) influencing cochlear structures, leading to an acquired (adventitious) hearing loss.

Parasitic infection transmitted across the placenta.
Greatest risk to the baby during the first trimester.
Causes congenital sensorineural loss ranging from mild to profound.
As much as 10 ext{%} - 20 ext{%} of congenital deafness is contributed to toxoplasmosis.
Parasite is found in cat feces, so pregnant women are counseled to avoid cleaning cat litter boxes.

Both bacterial and viral forms exist, but the bacterial form is far more damaging to the ear.
It is the inflammation/swelling of the lining of the brain and spinal cord (meninges).
Because the brain is involved, deafness, blindness, coma, and damage to motor centers of the brain can occur.
HL due to meningitis typically leads to a cochlear implant rather than a hearing aid because the electrode array must be inserted into the cochlea before it calcifies.
The presence of a calcified cochlea would make implantation of the electrode array unsuccessful.

The most common viral cause of congenital hearing loss.
$40\%-50\%$ of infected mothers will pass CMV on to their infants.
More damaging to hearing in a developing fetus than to hearing in an individual after birth.
Can cause vision loss, progressive sensorineural hearing loss, and cognitive delays.

Both are covered in the chapter on acquired hearing loss (Bb) and are discussed in relation to congenital risk.
Syphilis is treatable with penicillin/antibiotics; Herpes is treated with antiviral drugs.
Syphilis is much more dangerous/serious than herpes.
Both lead to greater hearing loss and damage to the fetus than if the infection occurred after birth.

Perinatal onset of hearing loss is possible.
Causes sensorineural hearing loss of varied degrees from mild to profound.
The problem: if the mother is not treated prenatally with Rhogam, the baby may require a complete blood transfusion, and during that transfusion there is a risk of anoxia (see next slide).
If Rhogam is not used and there is no transfusion, the baby may die.

Anoxia is a lack of oxygen.
If oxygen is not reaching the cochlea, cochlear structures can be damaged.
Additionally, lack of oxygen to the brain can cause central forms of hearing loss.
ANOXIA/ ASHYXIATION causes perinatal onset of hearing loss and results in sensorineural hearing loss of varied degrees from mild to profound.
NOTE: This condition will likely also cause visual problems and cognitive concerns.