THORACIC INTRA-DURAL ARACHNOID CYST

The authors report a case of indradural posterolateral spinal arachnoi d 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 examinat ion 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 par aparesis with a right predominance. On MRI, the spinal cord was displa ced at T6-T7 level by a posterior intradural mass with a similar signa l than CSF; futhermore, at this level, there was an intramedullary hyp osignal on T1 weighted sections. The diagnosis of spinal intradural ar achnoid cyst was confirmed at surgery. Microscopic examination of the cyst wall showed fibrous tissue with mild lymphocytic infiltration. Ra pid recovery of legs weakness followed, but abnormalities of spinothal amic fonctions persisted. The clinical caracteristics and the MRI data are discussed. The authors conclude that this arachnoid cyst had an i nflammatory origin.