[Symptomatic spinal intra-dural arachnoid cyst. Apropos of a case with magnetic resonance imaging].

The authors report a case of intradural posterolateral spinal arachnoid cyst diagnosed by Magnetic Resonance Imaging (MRI) in a 59-year-old woman. Ten years before, she started to suffer from burning sensation of the left lower limb aggravated by head movements. Physical examination was normal except a sensory dissociation below T10. A myelography was considered as normal. Three years later, motor disturbances occur with progressive weakness. Examination showed asymmetrical spastic paraparesis with a right predominance. On MRI, the spinal cord was displaced at T6-T7 level by a posterior intradural mass with a similar signal than CSF; furthermore, at this level, there was an intramedullary hyposignal on T1 weighted sections. The diagnosis of spinal intradural arachnoid cyst was confirmed at surgery. Microscopic examination of the cyst wall showed fibrous tissue with mild lymphocytic infiltration. Rapid recovery of legs weakness followed, but abnormalities of spinothalamic functions persisted. The clinical characteristics and the MRI data are discussed. The authors conclude that this arachnoid cyst had an inflammatory origin.