正中神経運動枝を選択的に障害した砂時計状ガングリオンの1例

Selective Median Nerve Motor Neuropathy Caused by a Dumbbell-shaped Ganglion in the Carpal Tunnel. Case Report

　症例は41歳の女性で，主訴は左手掌部の腫瘤であった．母指球皮線撓側に1.5cmの弾性硬の腫瘤を認め，短母指外転筋の高度萎縮を認めた．正中神経領域の感覚障害は認めなかった．MRIでは中手骨基部掌側でくびれた部分を持つ，T1強調像で低信号，T2強調像で一様な高信号の軟部腫瘤を認めた．摘出術を施行し，術中にガングリオンが手根管内で正中神経の運動枝分岐部を圧迫し，横手根靱帯を運動枝とともに貫通している所見を認めた．ガングリオンにより正中神経運動枝が選択的に障害された非常に稀な症例と考えられた．

　Carpal tunnel syndrome is one of the most common peripheral compressive neuropathies, and sensory symptoms typically predominate at presentation, with motor dysfunction being seen in chronic cases.　Isolated motor dysfunction, however, is rare.　We report a case of selective median nerve motor neuropathy caused by a dumbbell-shaped ganglion in the carpal tunnel.　A 41-year-old female presented with a lump in the palm of her left hand that made controlling her left thumb difficult.　There was no numbness or sensory loss.　Magnetic resonance imaging identified a dumbbell-shaped cystic lesion in the carpal tunnel.　Intraoperative exploration revealed that the ganglion originated in the scaphoid-trapezium joint and that it protruded between the thenar muscles through the transverse metacarpal ligament and was compressing the motor branch of the median nerve.　The patient had not recovered from the thenar muscle weakness as of 6 months after resection of the ganglion.