Noncommunicating spinal extradural arachnoid cyst causing spinal cord compression in a child.

Extradural arachnoid cysts in the spine are relatively uncommon causes of spinal cord compression in the pediatric population that are thought to arise from congenital defects in the dura mater. Most reports describe such cysts communicating with the intrathecal subarachnoid space through a small defect in the dura. The authors describe the case of a child who presented with spinal cord compression caused by a large spinal extradural arachnoid cyst that did not communicate with the intradural subarachnoid space. An 11-year-old girl presented with urinary urgency, progressive lower-extremity weakness, myelopathy, and severe gait ataxia. Magnetic resonance imaging of the spine demonstrated a large extradural arachnoid cyst extending from T-8 to T-12. The patient underwent a thoracic laminoplasty for en bloc resection of the spinal extradural arachnoid cyst. Intraoperatively, the dura was intact and there was no evidence of communication into the intradural subarachnoid space. Postoperatively, the patient's motor strength and ambulation improved immediately, and no subsequent cerebrospinal fluid leak occurred. Noncommunicating spinal extradural arachnoid cysts are extremely rare lesions that can cause spinal cord compression in children. Because the dura remains intact, they can be removed entirely without subsequent dural repair. The authors review the literature and discuss the proposed underlying mechanisms of formation of these arachnoid cysts.