Distribution of low-frequency nerve fibers in the auditory nerve: Temporal bone findings and clinical implications.
OBJECTIVE
Low-frequency cochlear fibers are on the outer surface of the auditory nerve adjacent to the vestibular nerve in the distal part of the internal auditory canal.


BACKGROUND
There is a misconception that low-frequency cochlear fibers are in the core of the cochlear nerve and are surrounded by high-frequency fibers.


METHODS
We analyzed temporal bones with a loss of upper spiral ganglion cells caused by different etiologies (n = 6) and traced the corresponding fibers into the distal internal auditory canal. Spiral ganglion cells for each segment (I-IV) of the cochlea were counted, and we defined the location of nerve fibers from the various segments.


RESULTS
There was total or near-total degeneration of the upper spiral ganglion cells in these bones. Corresponding low-frequency fibers were on the outer surface of the cochlear nerve adjacent to the vestibular nerve in the distal segment of the internal auditory canal.


CONCLUSIONS
Low-frequency fibers seem to be located at the periphery of the cochlear nerve. These findings provide one possible explanation for the low-frequency sensorineural hearing loss found in 10% of patients with vestibular nerve schwannomas and may have clinical relevance in the diagnosis of these lesions.
Fayad
Jose N
JN
Department of Histopathology, Temporal Bone Laboratory, House Ear Institute, Los Angeles, California 90057, USA. jfayad@hei.org
Don
Manny
M
Linthicum
Fred H
FH
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001309:Auditory Threshold / Q000502:physiology*; D002452:Cell Count; D003056:Cochlear Nerve / Q000033:anatomy & histology* / Q000502:physiology; D005260:Female; D034381:Hearing Loss / Q000503:physiopathology; D006801:Humans; D008875:Middle Aged; D009412:Nerve Fibers / Q000502:physiology*; D013136:Spiral Ganglion / Q000473:pathology