Clinicopathological Studies in Presbycusis

Abstract

Presbycusis is one of the most interesting problems in gerontology. Many pathological, physiological and audiological works have been reported, but the exact nature of presbycusis is still obscure.
Pure tone audiometric tests were performed on 239 patients using the same audiometer.
On 105 autopsy cases of which 35 cases were examined audiometrically before death, temporal bones and brains were served for pathological studies. The sections of the temporal bones were graphically reconstructed, and the audiometrical and morphological data were compared on parallel coordinate.
Severity of encephalomalacia and spongy change in the central auditory pathway and atrophy of the general organs were watched carefully. Furthermore arteriosclerosis of the aorta, cerebral artery, internal' auditory artery and renal artery were examined. The significance of those findings on the development of hearing loss were observed.
Periods from audiometric examination to autopsy were less than 11 months, and the functional and morphological data could be compared with reasonable accuracy.
The conclusions were as follows:
1) Type of hearing in presbycusis was classified into seven kinds, i. e., type A (normal audiometric curve), type B (flat curve), type C (abrupt curve), type D (descending curve), type E (convex upwards curve), type Dip and type F (ascending curve). Type D, B and C together occupied the greater part of the examined cases.
2) The most conspicuous change in the temporal bones of old people was the atrophy of spiral ganglion. Besides, there were observed atrophy of stria vascularis and destruction of hair cells.
3) Atrophy, spongy change and encephalomalacia were observed in central auditory pathway especially in the central part of eighth cranial nerve, cochlear nuclei and transverse temporal gyri.
4) Lumen narrowing of internal auditory artery with varing degree was observed in almost all cases of old people, which was conspicuous in the cases with severe arteriosclerosis of cerebral artery.
5) Lumen narrowing of internal auditory artery was supposed to have positive correlation with atrophy of spiral ganglion and hearing loss.
6) Hearing loss was supposed to have positive correlation with atrophy of brain and spongy change of transverse temporal gyri. Many cases of encephalomalacia showed high degree of hearing loss.
7) The development of the above mentioned types of hearing was based on the atrophy of spiral ganglion and the so-called “type factors” and “level down” of auditory acuity was supposed to be due to the effect of cerebral degeneration.
8) Type B (flat curve) was supposed to be an audiometric image influenced by the cerebral degeneration, type C (abrupt curve) was that affected by the acoustic trauma, and type D (descending curve) was that influenced by the atrophy of spiral ganglion and degeneration of eighth cranial nerve.
9) Changes in temporal bones and central auditory pathway was considered to be caused by senile atrophy and arteriosclerosis.
10) Internal auditory artery branched most frequently off from inferior anterior cerebellar artery except for some cases where it directly diverged from basilar artery.