[Failure to preserve hearing in XXXX surgery: experiences after introduction of MRI].

@entity1 @entity5513 @entity5 @entity55197 @entity393
This report elucidates our experiences on @entity5513 surgery, in which auditory function was lost postoperatively, although conservation of hearing had been intended preoperatively. Five ears from four @entity1 (two ears: unilateral, three ears from bilateral @entity5513 ) were operated on via standard retromastoid route, with monitoring of auditory evoked potentials. Abolition of @entity55197 occurred when surgical manipulations were performed within the internal auditory canal. Pulling @entity5 tissue away from the cochlea toward the brain stem has proved to be a hazardous procedure. Recognizing the condition of @entity5 tissue within the internal auditory canal is prerequisite for hearing preservation. For this purpose, MRI is very useful because @entity5 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 @entity5513 with a diameter of more than 10mm cannot be resected without causing loss of hearing, and, even in such small @entity5 , the cochlear nerves are infiltrated by @entity5 cells. Most @entity55197 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 @entity55197 indicated that progression of degeneration of the cochlear nerve fibers occurred after surgery. This phenomenon may explain postoperative delayed @entity393 observed clinically.
