Temporal bone histopathologic abnormalities associated with mitochondrial mutation T7511C.

OBJECTIVES: We previously reported a mitochondrial T7511C mutation in the tRNA gene in a Japanese family with nonsyndromic hearing loss (HL). However, the temporal bone histopathology associated with T7511C has not been reported. The aim of the present study is to report histopathologic findings of a temporal bone from a patient in the Japanese family with this mutation. STUDY DESIGN: Single case study. METHODS: A temporal bone was obtained from the right ear of a male subject with progressive HL from 5 years of age and who died at 60 years of age from cerebral infarction. The bone was embedded, sectioned, and stained with hematoxylin-eosin for light microscopic study. Graphic reconstruction of the cochlea was performed using the method described by Schuknecht to determine loss of the stria vascularis and neurosensory elements including hair cells and spiral ganglion neurons. RESULTS: The most significant histopathologic finding was severe loss of spiral ganglion cells in all turns of the cochlea. Severe loss of neuronal filaments in Rosenthal's canal was also observed. The organ of Corti showed scattered loss of inner and outer hair cells in the basal turn. Partial atrophy of the stria vascularis was observed in all turns of the cochlea. CONCLUSION: Our results suggest that severe loss of spiral ganglion cells was the main cause of sensorineural HL associated with the T7511C mutation.