Spinal Intradural Arachnoid Webs Causing Spinal Cord Compression with Inconclusive Preoperative Imaging: A Report of 3 Cases and a Review of the Literature.

OBJECTIVE: Spinal arachnoid webs are a rare variant of spinal arachnoid cysts where 1 or multiple focal membranes of arachnoid tissue obstruct the subarachnoid space. Only 11 prior cases of arachnoid webs have been reported in the literature. We present a series of 3 consecutive cases of arachnoid webs from our institution and review the literature on this rare condition to provide recommendations for its management.

METHODS: Retrospective chart review was performed for 3 consecutive cases of intradural arachnoid webs causing spinal cord compression at our institution, with inconclusive preoperative imaging, treatment with surgical decompression, and resection. There were no external sources of funding.

RESULTS: Our cases occurred dorsally in the thoracic spine and were associated with syringomyelia. Preoperative magnetic resonance imaging, computed tomography myelography, and cine magnetic resonance imaging were inconclusive, and the definitive diagnosis was made with intraoperative ultrasound. Patients underwent laminectomies and resection of arachnoid webs. Unique from prior reports of arachnoid webs, the webs in the present cases were composed of multiple septated longitudinal membranes rather than a transverse band. All patients had improvement of presenting symptoms postoperatively.

CONCLUSIONS: Intradural arachnoid webs causing spinal cord compression are rare. Preoperative imaging may be inconclusive. Because of the septated longitudinal nature of the visualized membranes, we propose a 1-way valve mechanism of cerebrospinal fluid obstruction causing gradual cord compression and resultant syringomyelia.