Classics from the laryngoscope.

This classic article meticulously detailed the spiral ganglion cell (SGC) populations in 100 patients with variable degrees of hearing loss and known diagnoses to assess the correlation with speech discrimination scores and to hypothesize upon the inherent ability to stimulate the remaining spiral ganglia successfully with cochlear implants. Important observations from this study were that spiral ganglion cell populations in excess of 20,000 had normal or near normal thresholds, whereas losses up to 40 dB had at least 15,000 cells, and those with losses in the range of 50 to 60 dB had at least 10,000 cells. Surprisingly, with counts as low as 10,000 SGCs, some speech discrimination is still possible, and with 20,000 SGCs, normal discrimination was possible. These findings were especially significant at the time of publication because animal studies had shown degeneration of SGCs following deafness. Opponents of cochlear implantation posited that implants would lead to further hair cell damage and subsequent loss of all SPCs, which would lead to failure of the cochlear implant. Following these early studies, much greater detail in understanding neuronal projections to sensory epithelium, survival, and regeneration have come to light. Fayad and Linthicum showed that in human temporal bones, hair cell loss did not necessarily correlate with SGC survival out to 3 years. These results did not correlate implant function with the number of surviving SGC counts. In fact, there was curiously an inverse relationship between function and SGCs. Recently, however, it has been shown, in a within-subjects study, that in patients with bilateral cochlear implants, the differences in SGC counts were directly correlated with word recognition scores in patients. The variability between different patients did not allow such good controls and accurate assessment. Clearly, we continue to learn much from carefully correlated histories and human histopathologic specimens. The continued studies of the human temporal bone are key in furthering our understanding.