Neuro-otologic findings in unilateral isolated narrow internal auditory meatus.
OBJECTIVE
To report neuro-otologic findings concerning the four nerves in the internal auditory meatus (IAM) in patients with isolated congenitally narrow IAM and explore the implications regarding ontogeny of the nerves in the IAM.


METHODS
Retrospective case series study.


METHODS
University hospital.


METHODS
Five consecutive patients between 1997 and 2002 with unilateral isolated narrow IAM demonstrated by high-resolution computed tomography whose chief complaint was hearing loss (1 male and 4 females, 4 right sides and 1 left; age range 5-37 years, mean 20 years; IAM diameter at the porus: 26-33% of that on the normal side).


METHODS
Functional studies concerning the VIIth cranial nerve and the three branches of the VIIIth cranial nerve.


RESULTS
In all ears, auditory brain stem responses were absent, the speech discrimination score was 0%, and otoacoustic emissions were absent or markedly reduced compared with those on the normal side. Caloric responses were absent in two ears, reduced in two ears, and normal in one ear. Galvanic body sway tests showed no responses in the two ears in which caloric responses were absent. Inferior vestibular nerve function was estimated as normal in all ears on the basis of vestibular evoked myogenic potential recordings. Facial nerve functions were normal in all patients.


CONCLUSIONS
In isolated congenital stenosis of IAM, dysfunction of each nerve in the IAM can occur independently. In the ontogeny of the VIIIth cranial nerve, the cochlear and superior vestibular nerves tended to be involved together, whereas the cochlear and inferior vestibular nerves appeared independent of each other.
Ito
Ken
K
Department of Otolaryngology, Faculty of Medicine, University of Tokyo, Tokyo, Japan. itoken-tky@umin.ac.jp
Suzuki
Sayaka
S
Murofushi
Toshihisa
T
Ishimoto
Shin-ichi
S
Iwasaki
Shinichi
S
Karino
Shotaro
S
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D004424:Ear Canal / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000473:pathology; D004594:Electrophysiology; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D034381:Hearing Loss / Q000209:etiology* / Q000503:physiopathology; D006319:Hearing Loss, Sensorineural / Q000209:etiology / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D017084:Otoacoustic Emissions, Spontaneous; D010469:Perceptual Distortion; D012189:Retrospective Studies; D013067:Speech Perception; D014057:Tomography, X-Ray Computed / Q000379:methods; D014722:Vestibule, Labyrinth / Q000503:physiopathology