Sensory and Neural Degeneration with Aging, as Seen in Microdissections of the Human Inner Ear

Presbycusis, the gradual loss of hearing that occurs with advancing age, is as subtle and complex as the aging process itself. Schuknecht’has suggested that there are four main types of presbycusis: 1) sensory, with primary loss of the hair cells of Corti’s organ; 2 ) neural, with primary degeneration of neurons of the cochlear nerve and central auditory pathways; 3 ) metabolic, with primary atrophy of the stria vascularis; and 4 ) mechanical, with primary changes in the physical properties of the basilar membrane. To these four might be added vascular presbycusis, characterized by loss of minute vessels supplying the spiral ligament, stria vascularis, and tympanic lip, of which metabolic presbycusis may prove to be a special case. Central presbycusis, with loss of neurons from the cochlear nucleus and other auditory centers of the brain, might also be classified as a distinct type, the term neural presbycusis being reserved for degeneration of first-order neurons of the cochlear nerve. Above all, it should be emphasized that the various types of presbycusis seldom, if ever, occur singly. Any attempt, therefore, to set up an exhaustive classification or a complete list of causative factors in presbycusis at this time is necessarily premature.