Complications of epidural anesthesia: MR appearance of abnormalities.

Eight patients with acquired intradural arachnoid abnormalities caused by epidural anesthesia were evaluated with magnetic resonance (MR) imaging (eight patients) and intraoperative ultrasound imaging (four patients). Subarachnoid cysts were found in the lower cervical and thoracic spine in six patients. Irregularity of the surface of the cord was noted in seven cases. Associated intramedullary cysts and myelomalacia were seen in two patients. Arachnoiditis was unsuspected clinically in four patients; findings at MR imaging first suggested the cause of the patients' symptoms. The underlying mechanism for the intradural and cord abnormalities in seven of the eight patients was a chemically induced arachnoiditis produced by the administration of epidural anesthesia; in the eight case, an infection introduced at the time of the epidural injection was the cause of the abnormalities. The authors postulate that the preservative agents in the vials of anesthetic may have been the causative factor of this inflammation in the majority of the cases.