[Failure to preserve hearing in acoustic neuroma surgery: experiences after introduction of MRI].
This report elucidates our experiences on acoustic neuroma surgery, in which auditory function was lost postoperatively, although conservation of hearing had been intended preoperatively. Five ears from four patients (two ears: unilateral, three ears from bilateral acoustic neuromas) were operated on via standard retromastoid route, with monitoring of auditory evoked potentials. Abolition of ABR occurred when surgical manipulations were performed within the internal auditory canal. Pulling tumor tissue away from the cochlea toward the brain stem has proved to be a hazardous procedure. Recognizing the condition of tumor tissue within the internal auditory canal is prerequisite for hearing preservation. For this purpose, MRI is very useful because tumor tissue within the internal auditory canal can be clearly visualized. The preoperative criteria in selecting candidates for hearing preservation operations should be more strict because most acoustic neuromas with a diameter of more than 10mm cannot be resected without causing loss of hearing, and, even in such small tumors, the cochlear nerves are infiltrated by tumor cells. Most ABR changes during operations seem to be explicable from avulsion of the cochlear nerve fibers and/or the internal auditory artery from the fundus of the internal auditory canal-the tractus spiralis foraminosus. Postoperative recordings of ABR indicated that progression of degeneration of the cochlear nerve fibers occurred after surgery. This phenomenon may explain postoperative delayed hearing loss observed clinically.
Sekiya
T
T
Department of Neurosurgery, Hirosaki University School of Medicine.
Iwabuchi
T
T
Suzuki
S
S
Hatayama
T
T
Ishii
M
M
Oda
N
N
D000293:Adolescent; D000328:Adult; D001933:Brain Stem / Q000503:physiopathology; D005072:Evoked Potentials, Auditory; D005260:Female; D006309:Hearing; D006311:Hearing Disorders / Q000209:etiology* / Q000503:physiopathology; D006801:Humans; D007430:Intraoperative Care; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D009464:Neuroma, Acoustic / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D011183:Postoperative Complications / Q000503:physiopathology