[Thoracic arachnoid cyst presenting incomplete features of Brown-Séquard syndrome: a case report].

Spinal intradural arachnoid cyst presenting incomplete features of Brown-Séquard syndrome is very rare. Only 6 cases have been reported. We report one in a thoracic lesion. A 42-year-old man noticed thermohypesthesia in his right leg, and monoparesis in his left leg. On admission, he presented incomplete features of Brown-Séquard syndrome below the Th7 level. MRI showed the spinal cord to be displaced antero-laterally to the right at Th6-7 level. Myelography and CT myelography failed to show the cyst wall, but an arachnoid cyst was totally removed with T5-8 osteoplastic laminotomy. Sensory disturbance has not changed postoperatively, but motor weakness in his left leg recovered within one month after the operation. No cystic lesion has been detected by MRI during the ten months since the operation. We investigated all seven cases in the literature including our case which showed incomplete features of Brown-Séquard syndrome. As regards to the location of the cyst, all cases were at the mid-thoracic level. And four cases were at the midline. These results suggest that the mechanism of Brown-Séquard syndrome associated with spinal arachnoid cyst may be related not only to the laterality of the lesion but also to the asymmetrical circulation in the watershed area.