Surgical Management of Thoracic Arachnoid Webs: A Ten Year Single Institution Case Series

Introduction: Spinal arachnoid webs are intradural extramedullary tissues, which can form constrictive bands or cysts, causing mass effect upon the spinal cord. The degree of arachnoid webbing can vary, ranging from mild indentation to severe cord compression with syringomyelia. Arachnoid webs are rare and little long-term data is available about the natural history and prognosis. The objective was to study patients with arachnoid webs at a single health system to establish the natural history and guide surgical decision-making.

Methods: The Mount Sinai Health System radiology database was queried for “arachnoid cyst”, “arachnoid web”, “scalpel sign”, “cord herniation”, “syrinx”, and “syringomyelia”. Neurosurgeon case logs were also searched to identify cases of surgical resection of arachnoid webs. A retrospective chart review was performed for demographic, clinical, pathology and surgical variables. Statistical analysis was performed, with p < 0.05 considered significant.

Results: A total of 127 arachnoid web cases were identified. The average age at presentation was 58.6 years. Arachnoid webs were characterized radiographically: Type 1 webs cause spinal cord deformity; Type 2 webs have deformity and myelomalacia; and Type 3 webs have deformity, myelomalacia and syrinx formation. The majority of cases (54%) were Type 1 webs and relatively indolent. Type 3 webs (14%) may represent a more aggressive process. The subset of patients with syringomyelia showed potential for radiographic and clinical progression. These arachnoid webs were most frequently formed near the T4 vertebral level. All cases that required surgery (32.3%) had pain or myelopathy. The majority of surgical patients experienced symptomatic improvement. Pathologic sampling revealed predominantly benign fibroconnective tissue with occasional hyalinization and/or calcification. 62.5% of cases with calcification/inflammation occurred in type 3 webs.

Conclusion : Our large case series of arachnoid cysts and webs demonstrates that most patients do not require surgery, but symptomatic patients benefit from surgical decompression.