聴神経腫瘍における聴力保存と手術中電気生理学的モニター

INTRAOPERATIVE ELECTROPHYSIOLOGICAL MONITORING FOR HEARING PRESERVATION IN ACOUSTIC NEURINOMA SURGERY

　抄録　5例の聴力保存を目的とした聴神経腫瘍手術で，聴覚脳幹反応（BAEP），蝸電位（ECoG），蝸牛神経活動電位（CAP VIII）により，聴覚路機能を各部位別に術中モニターした。全例で形態的に蝸牛神経が温存されたが，うち2例で，V波を含めたBAEPが術中保存され，このうち1例でのみ有用な聴力が温存された。CAP VIIIとECoGは種々のパターンを示した。聴力障害例では，冬電位の障害のパターンの違いにより，術中聴力障害を生じさせた手術操作と障害部位の推定が可能であった。この結果，術中種々の部位で聴覚路が障害されることが明らかとなり，これらの検討は聴力保存のために必要な手術操作の注意点を警告し，次回の手術での聴力保存に役立つと考えられた。また有用な会話レベルの聴力保存のため，モニター上はBAEPのV波を含めてこれらすべての反応の保存を心掛ける必要がある。聴力障害の予防のため手術操作にreal timeにfeed backされるモニターとして，BAEPは，急速な障害の進行をとらえられず，障害の予防に役立たなかった。これに対してECoG, CAP VIIIは，よりreal timeなモニターが可能であったが，その有用性についてはさらに検討が必要である。

Five acoustic neurinomas have been operated with hearing preservation as a goal. We monitored intraoperative brainstem auditory evoked poten-tials (BAEP) in all five cases, electrocochleogram (ECoG) using needle electrode in external auditory meatus in four, and compound action potentials directly recorded from the cochlear nerve (CAP VIII) in three. In all five cases the tumor was totally resected and cochlear nerve was anatomically pre-served. However, in only one case useful hearing was preservated with preservation of all wave forms of the BAEP. Another patient with preser-vation of all wave forms of BAEP and the ECoG showed postoperative severe hearing loss. Other three patients showed postoperative severe hearing loss : only Wave I of BAEP and ECoG were preserved without preservation of the CAP VIII in one whose cochlear nerve was thought to be da-maged in cerebellopontine angle cistern ; Wave I of BAEP, ECoG and CAP VIII were preserved in one in whom it was suggested cochlear nerve near brainstem or cochlear nucleus was demagged ; none of the BAEP, ECoG and CAP VIII was pre-served in one in whom it was suggested distalcochlear nerve, or internal auditory artery was damaged. These different patterns of changes suggested that different causes for the hearing loss and difficulties in hearing preservation during acoustic neurinoma surgery. Having identified the putative mechanism of the hearing loss by monitoring those potentials, suggestions are made about how such hearing loss might be avoided.

For preservation of the hearing in acoustic neu-rinoma srugery, all of those potentials including all wave forms of BAEP, ECoG and CAP VIII should be preserved during surgery.

ECoG and CAP VIII were more rapid indicators of the reversible trauma to the auditory nerve than BAEP. It is suggested that monitoring those potentials may help to prevent injury to the audi-tory nerve.