両側難聴で発症した脳幹・小脳梗塞の1例―聴性脳幹反応の経時的観察による難聴の責任病巣の考察

A Case of Infarction in Brainstem and Cerebellum as a Initial Symptom with Bilateral Hearing Loss

　両側性の難聴を呈し，両側小脳および脳幹に梗塞巣を認めた症例を経験した。症例は56歳男性。浮動性眩暈，歩行障害，両側難聴，耳鳴にて発症。頭部MRI上，両側中小脳脚，両側小脳半球，右大脳脚に拡散強調画像にて高信号病変を認め，頭頸部の3D-CTアンギオでは，両側椎骨動脈に高度の狭窄を認めた。第14病日の聴性脳幹反応（ABR）では，両側ともII波からV波まで消失していたが，第61病日にはI波からV波まで全波が認められた。ABRの結果から，難聴の責任病巣として，橋下部聴神経線維のほか，蝸牛神経の障害が推定された。既報告例と同様に，本症例の難聴の予後は比較的良好であったが，その原因として，本症例が高度の両側椎骨動脈狭窄を基盤とした血行力学的機序によって起きた脳梗塞であり，梗塞部位への側副血行路からの血流が，可逆的な聴力変化をもたらした可能性が考えられた。

　A 56-year old male presented with a sudden onset of bilateral hearing difficulty. He complained of dizziness and gait disturbance at the onset and subsequently developed bilateral hearing loss and tinnitus. Brain MRI revealed multiple infarcts in bilateral middle cerebellar peduncles, bilateral cerebellar hemispheres and the right cerebral peduncle. Three dimentional computed tomography　angiography（3D-CTA）showed severe stenosis of bilateral vertebral arteries. Infarcts were located in the border zone between anterior inferior cerebellar artery （AICA） and superior cerebellar artery （SCA）, suggesting hemodynamic infarctions. Auditory brain stem responses （ABR） were recorded three times. The initial ABR demonstrated all waves except for wave I on day 14. Wave I on the left was normal, while wave I peak latency on the right was prolonged. On day 61, all waves were recorded, although peak latencies of waves III to V and interpeak intervals of the wave I to III on the right side were prolonged. Involvements of the cochlear nerve and pontine auditory pathway were suggested from the ABR abnormalities in this case.