The Inner Ear and Diseases of the Bony Labyrinth

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Last modified 22/03/2015

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Chapter 633 The Inner Ear and Diseases of the Bony Labyrinth

Genetic factors can affect the anatomy and function of the inner ear. Infectious agents, including viruses, bacteria, and protozoa, also can cause abnormal function, most commonly as sequelae of congenital infection or bacterial meningitis. Other acquired diseases of the labyrinthine capsule include otosclerosis, osteopetrosis, Langerhans’ cell histiocytosis, fibrous dysplasia, and other types of bony dysplasia. All of these can cause both conductive and sensorineural hearing loss as well as vestibular dysfunction. Use of currently available vaccines reduces the risk for bacterial meningitis and the associated sensorineural hearing loss.

Viruses

The most common cause of childhood sensorineural hearing loss (SNHL) is congenital cytomegalovirus (CMV) infection (Chapter 247). The strongest predictor of delayed hearing loss appears to be the presence of symptoms at birth; prolonged viral shedding may also be a risk factor. In one large study, children who passed initial audiologic examinations but who had CMV-related symptoms at birth were ~6 times more likely to develop hearing loss than those who were asymptomatic. Stabilization or perhaps reversal of the hearing loss may be possible by using ganciclovir in very young infants with congenital CMV infection.

Other viral causes of SNHL include congenital rubella as well as acquired mumps, rubella, rubeola (measles), and fifth disease, caused by parvovirus B19. Many other viruses also occasionally are associated with SNHL. In as many as 50% of cases, hearing loss, which usually is bilateral and often is asymmetric, progresses and worsens over weeks to years.

Before an effective vaccine was introduced, rubella was responsible for as many as 60% of cases of childhood SNHL. Vaccination in developed countries has reduced the rate of rubella by >97%. Similarly, measles and mumps are now uncommon causes of SNHL in the USA because of successful vaccination programs.

Herpes simplex encephalitis can also be associated with SNHL, which is more common in children with congenital herpesvirus infection. Acyclovir and other antiviral agents can help the hearing loss and other central nervous system manifestations (Chapter 237).