Arachnoid web-a rare but surgically effectively treatable cause of spinal cord compression and syringomyelia.

Objective: Dorsal arachnoid web (AW) is a rare cause of spinal cord compression, which is indicated on MRI by a dorsal indentation of the spinal cord (scalpel-sign). AW can be associated with a myelon lesion as a sign of secondary syringomyelia resulting from alterations of CSF flow-dynamics. The etiology of AW is unclear, and evidence-based treatment recommendations are still lacking. Methods: A retrospective chart study was conducted on patients with the scalpel-sign, treated at a tertiary neurospine center between 2016 and 2024. Clinical presentation, imaging, and histopathological findings were evaluated, and treatment outcome was assessed using the thoracic Japanese Orthopedic Association (tJOA) score pre- and postoperatively, and anatomically and pathophysiologically contributing factors are discussed. Results: 17 patients (mean age 55.5 ± 10.3 yrs, 9 males) were identified. Predilection site was the upper half of the thoracic spine, with additional syringomyelia in 9 patients (53 %). 10 patients (65 %) showed sensory deficits, 10 (59 %) motor symptoms, 10 (59 %) ataxia, 9 (53 %) back pain, and 7 (41 %) neuropathic pain. 10 (59 %) patients underwent surgery with web removal/adhesiolysis. Median follow-up was 176 days. Postoperatively, symptoms worsened in one patient, but improved in the majority of cases (mean tJOA pre-/postoperatively: 8 ± 1.1/9.2 ± 1.3; Wilcoxon signed-rank-test p < .02), with postoperative MRI showing regression of AW and syringomyelia. Conclusion: Surgical intervention appeared beneficial in the majority of patients, even in those with longstanding symptoms and resulting in regression of spinal cord lesions. Awareness of AW should be raised, as it identifies a rare but effectively treatable cause of spinal cord compression and syringomyelia.