ABSTRACT
The purpose of this study is to increase the knowledge of the spiral ganglion in relation to hearing, discrimination, normal deterioration of age, and other pathologies encountered in the study of the temporal bones. After a brief analysis of previous research on the spiral ganglion the author builds a model to study different available methods of assessign spiral ganglion population. Counting ganglion cells in one of each 10 section, 20 microns width seems to be the best method. From the collection of more than 900 temporal bones of Prof Schuknbecht at the Mass. Eye & Ear Infirmary, one hundred cases were selected. Ninety eight to these cases had a previous audiogram with discrimination priorto death. Pathology of these cases had been studied by Prof. Schuknecht. At the same time, some anatomical and hystological observations were made, studying the normal deterioration of the ganglion cells according to age, and its relation to hearing and discrimination. In relation to age, a linear deterioration from the first to the ningth decade of life was found uniformly distributed among the segments. The minimum number of cells necessary to preserve hearing was also determined. For instante, 22.000 cells are required for 10 dB or better hearing: 10.000 cells are necessary for 50 dB or better hearing. Although it is hard to relate ganglion cells to discrimination, it appears that to attain a PB Score of 80 percent or better, at least 18.000 cells are required. When comparing the number of ganglion cells of each segment with discrimination, a closer relation with the apical segment is apparent. The total number of cells and the number of cells in each segment of three normal subjects under 10 year of age was compared with the following cases: Under 80 years old, neural prebycusis, strial atrophy. Meniere's disease, otoesclerosis and middle age individuals with normal hearing. No significant variations among these pathologies were found. In contrast, guinea pigs with experimentally induced labyrinthine hydrosp showed and evident ganglion cell loss in the apical coil. Each of the findings of this study are discussed in relation to previous reports