聴神経腫瘍手術における聴力の保存と術後聴力

PRESERVATION OF HEARING AND POST-OPERATIVE AUDIOLOGICAL FINDINGS IN ACOUSTIC TUMOR SURGERY

　I．はじめに

　聴神経腫瘍（以下ATと略す）の術後に聴力が保存されるようになったのは，Houseら^8,9）により早期診断と中頭蓋窩経由法（middle cranialfossa approach，以下MF法と略す）が積極的に行われるようになった最近約10年のことである。

　近年，早期診断技術の向上，手術技術の進歩，非腫瘍側に難聴がある症例や両側AT例（Recklinghausen病）などの経験から，機能保存への関心が高まりつつある^12）。従来の報告はどちらかというと，術後の聴力保存に関する技術的なものが多く，腫瘍の大きさとの関係，手術方法に関するものが多い^{6,7,19,21,24）}。しかし，聴力が保存される例が増加するにつれ，術後の聴力の質的な面，すなわち，聴覚機能の変化に関心が向かうのは当然である。しかし，このような報告は少なく，Houseら^8,9）。Harkerら^7）のものをみるにすぎない。

　1) Out of twenty-eight cases with acoustic tumors and a case with suspected facial neuroma, hearing was preserved in nine cases. In five out of nine cases, pre-operative hearing level was preserved, and in one case hearing was improved post-operatively. In three cases, hearing was spared but deteriorated comparing with pre-operative hearing level.

　2) In four out of eight intracanalicular neuromas, pre-operative hearing level was preserved and in one case, hearing improved post-operatively.

　3) In two cases with extradural neuroma, hearing was preserved.

　4) Cases in which pre-operative hearing level was spared, were all operated on through the middle cranial fossa approach.

　5) Three out of four cases in which pre-operative stapedius reflex (SR) decay was positive were became negative post-operatively. These cases included two extradural neuromas extending anteriorly from the internal auditory canal and a case with posterior fossa acoustic neuroma, in which pure tone hearing threshold was deteriorated. Therefore, SR decay test has a diagnostic value for detection of early tumor, because positive decay may be a sign sugessting the compression of tumor mass to the cochlear nerve.

　6) In Recklinghausen's disease or acoustic tumor extending to the posterior fossa, hearing preservation is generally difficult.

　7) In cerebellopontine angle tumor other than acoustic neuroma, on the other hand, hearing improvement was remarkable post-operatively compared with acoustic tumor.

　8) To preserve hearing post-operatively, it is hoped that acoustic tumors should be found out in the early stage in which tumor is confined to the internal auditory canal, and middle cranial fossa approach will be applied.