前側頭葉切除術の前後におけるDichotic Listening Testの変化

EFFECTS OF UNILATERAL TEMPORAL LOBECTOMY ON VERBAL DICHOTIC LISTENING TEST

　難治のてんかん発作の治療のために，前側頭葉切除術を行った左大脳半球言語優位の側頭葉てんかん患者25例に対し，術前と術後に言語性のDichotic Listening Testを施行し，以下の結果を得た。1）術前には，右側頭葉切除群（R-TLE群）と左側頭葉切除群（L-TLE群）は同程度に右耳優位であった。正答数はL-TLE群がR-TLE群より低かった。2）術後にR-TLE群，L-TLE群ともに切除側の反対側耳の言語音認知能力の低下は見られなかった。3）術後の優位性はL-TLE群では左耳に変換し，R-TLE群では右耳優位が術前よりさらに顕著になった。すなわち術後には切除側と同側耳の言語音認知能力が上昇した。

　以上から，前側頭葉切除術では，いわゆるlesion effectは生じず，むしろ，切除側の同側耳の認知能力の改善がみられると推定された。てんかん原性焦点に由来する発作放電が終熄した結果と考えられる。

Verbal dichotic listening test was conducted before and after anterior temporal lobectomy on 25 patients who underwent the operation because of their medication-resistant epileptic seizures. Their speech dominance by Wada test was all left sided.

1. Preoperatively, patients having the epilep-togenic focus in the right temporal lobe (R-TLE) and those having the focus in the left (L-TLE) were, as expected, all right-ear dominant. The mean number of correct responses was fewer in L-TLE than in R-TLE group.

2. Postoperatively, no detrimental effects for recognition of verbal auditory stimuli by the ear contralateral to the focus was observed both in L-TLE and in R-TLE group.

3. Postoperatively, the ear-dominance shifted : to the left in patients with L-TLE, and to the right more conspicuously in patients with R-TLE compared to the preoperative scores. In other words, the recognition ability by the ears ipsila-teral to the side of focus, or of resected temporal lobe, was ameliorated.

Summarizing, the unilateral anterior temporal lobectomy did not cause "lesion effect" but yielded improvement of verbal auditory recognition by ears ipsilateral to the epileptogenic focus. Dimini-shed epileptic bombardment resulted in by the resection surgery may be a possible explanation.