Symptomatic Large Spinal Extradural Arachnoid Cyst: A Case Report

Spinal extradural arachnoid cysts (SEACs) are relatively rare cause of compressive myelopathy. SEACs can be either congenital or acquired, but the etiology and the mechanism for their development are still unclear. A number of cases have been reported in the literature, and the one-way valve mechanism is the most widely accepted theory which explains the expansion of cysts and spinal cord compression. We report two cases of SEAC in this article. Patients had intermittent, progressive cord compressing symptoms. MRI image showed large SEAC which caused compression of the spinal cord. Pre-operative cystography and CT myelography were performed to identify the communicating tract. Pre-operative epidural cystography showed a fistulous tract. The patients underwent primary closure of the dural defect which was a communicating tract. The operative finding (nerve root herniation through the tract) suggested that the SEAC developed through a checkvalve mechanism. Postoperatively, the patients had no surgical complications and symptoms were relieved. Based on our experience, preoperative identification of the communicating tract is important in surgical planning. Although surgical excision is the standard surgical treatment, primary closure of the dural defect which was a communicating tract can be an acceptable surgical strategy.