The cochlea of a neonate may have been damaged in utero by rubella in the pregnant mother. Mumps, acute purulent meningitis (particularly from Pneumococcus and Haemophilus), or chronic infection spreading from the middle to the inner ear may cause nerve deafness in childhood. The meningeal infection spreads along the cochlear aqueduct, a structure that connects the cerebrospinal fluid (CSF) space with the perilymph of the cochlea. Measles vaccination, Mycoplasma pneumoniae infection, and scarlet fever have been associated with acute deafness, with or without vestibular symptoms. It is uncertain whether the deafness in these cases is due to direct infection of the cochlea or represents an autoimmune reaction directed to the inner ear. Also, the inner ear contains melanocytes, and their involvement in Vogt-Koyanagi-Harada disease adds dysacusis, tinnitus, and sensorineural deafness to the usual manifestations of vitiligo of the eyebrows, poliosis (depigmented forelock of hair), iritis, retinal depigmentation, and recurrent meningitis. Meningeal hemosiderosis, a rare process that results from repeated bouts of subarachnoid hemorrhage, also causes eighth nerve damage and deafness, presumably as a toxic effect of iron deposition in the meninges adjacent to the nerve. Cases of acute sensorineural hearing loss or reduced acuity have occurred following CSF drainage or lumbar puncture, likely either the result of traction on the cochlear nerve due to pressure gradients, or endolymphatic hydrops (see further on) through a patent cochlear aqueduct. Most cases are transient.
Episodic deafness in one ear, even without vertigo, proves in most instances to be the result of Ménière disease (see further on).
Otologists have described a progressive sensorineural type of hearing loss as a late manifestation of congenital syphilis, sometimes occurring despite prior treatment with adequate doses of penicillin. It has been claimed that the long-term administration of steroids may be useful in such cases. The pathologic basis of the hearing loss has not been determined and the causal relationship to congenital syphilis remains to be established.
The auditory nerve may be involved by tumors of the cerebellopontine angle or by mycotic, lymphomatous, carcinomatous, tuberculous, Listeria, melioidosis, or other types of chronic meningitis and rarely, in sarcoidosis. Lymphomatous meningitis has a particular predilection to cause unilateral hearing loss; we have seen several such cases in which no other cranial nerves were infiltrated. Carcinomatous meningitis may do the same but almost always in the context of other cranial and spinal nerve palsies (see Chap. 31). Of the solid tumors, the ones that involve the auditory nerve most frequently are schwannomas, neurofibromas, meningiomas, dermoids, and metastatic carcinoma. In neurofibromatosis type II, the involvement by vestibular and acoustic schwannomas is typically bilateral as discussed in Chap. 37. Unilateral deafness may also result from demyelinative plaques, infarction, or tumor involving the cochlear nerve fibers or nuclei in the brainstem. Rarely, deafness is the result of bilateral lesions of the temporal lobes (see Chap. 22). The condition called pure word deafness, a type of aphasia, is also caused by left temporal lobe disease; despite normal pure-tone perception and audiometry and normal brainstem auditory evoked potentials, spoken words cannot be understood. This condition is discussed in Chap. 23.