A Novel Clinical Insight Into Idiopathic Syringomyelia With Occult Arachnoid Webs: Neuropathological Features, Differential Diagnosis, and Surgical Strategy.

Objective: Idiopathic syringomyelia (IS) associated with occult arachnoid pathology is a relatively rare condition characterized by a subtle onset, atypical clinical manifestations, and significant diagnostic and therapeutic challenges. This study aims to evaluate the radiographic and clinicopathological features of IS to improve surgical management and patient outcomes.

Methods: In this study, clinical and radiologic data were retrospectively extracted from a single-center syringomyelia database (N=1,039) spanning December 2020 to March 2025. Among these, 15 patients diagnosed with IS underwent preoperative magnetic resonance imaging and myelography to identify the responsible spinal segments precisely. Comprehensive perioperative assessments and clinical outcomes were collected. During surgery, the subarachnoid space (SAS) was thoroughly explored, with complete removal of thickened and adherent arachnoid tissue to restore normal cerebrospinal fluid (CSF) circulation. Additionally, clinical data, pathological features, and surgical outcomes of IS were compared to those of posttraumatic delayed syringomyelia (PTDS) to evaluate potential differences.

Results: In this series, all patients underwent preoperative myelography, revealing varying degrees of SAS obstruction. For IS cases that received precise and comprehensive arachnoid lysis, overall postoperative outcomes were favorable. Intraoperative pathology confirmed that all IS cases were characterized by noninfectious, nonacute inflammation. The preoperative maximal syrinx/cord ratio averaged 0.70±0.07 (range, 0.54-0.88), while the syrinx resolution rate varied from 12.2% to 100%, with a mean improvement of 29.6%. Patients with PTDS exhibited a relatively higher incidence of hypesthesia and a greater syrinx tension index. However, no significant differences were observed between IS and PTDS in terms of syrinx length, deviation, or location. Notably, the IS group demonstrated significantly better postoperative syrinx resolution and improvement in syringomyelia-related symptoms compared to the PTDS group.

Conclusion: While both IS and PTDS share a common underlying mechanism of arachnoid adhesions, they differ significantly in pathological features, treatment approaches, and clinical outcomes. In cases of IS, thorough spinal arachnoid lysis at the affected segment could restore normal spinal cord pulsation and CSF circulation, leading to effective syrinx resolution and a favorable long-term prognosis.