Spinal arachnoid webs are a rare variant of spinal arachnoid cysts where one or multiple focal membranes of arachnoid tissue obstruct the subarachnoid space. Only 11 prior cases of arachnoid webs have been reported in the literature.

Three consecutive cases of intradural arachnoid webs causing spinal cord compression, with inconclusive preoperative imaging, treatment with surgical decompression and resection. There were no external sources of funding.

The cases occurred dorsally in the thoracic spine and were associated with syringomyelia. Preoperative MR, CT myelogram, and cine MR were inconclusive, and the definitive diagnosis was only made with intraoperative ultrasound. The patients underwent laminectomies and resection of arachnoid webs. Unique from prior reports of arachnoid webs, the webs the presented cases comprised of multiple septated longitudinal membranes rather than a transverse band. All patients had improvement of their presenting symptoms postoperatively.

Intradural arachnoid webs causing spinal cord compression is rare; preoperative imaging may be inconclusive. Because of the septated longitudinal nature of the visualized membranes, Zhang propose a one-way valve mechanism of CSF obstruction causing gradual cord compression and resultant syringomyelia ¹⁾.