Arachnoid Web With Atypical Imaging Findings and Clinical Manifestations: A Case Report.

Spinal arachnoid web (SAW) is a rare intradural lesion that can result in spinal cord compression and myelopathy. This report describes a case of SAW with atypical imaging findings and clinical manifestations in a 63-year-old male patient who presented with progressive lower limb paresthesia and left-dominant muscle weakness. The patient also exhibited temperature and pain sensory disturbances in the right leg. Magnetic resonance imaging (MRI) revealed spinal cord atrophy, intramedullary hyperintensity, and a dorsal flow void without the scalpel sign at the T7 level. Laminectomy and surgical resection of the SAW were performed. Intraoperative ultrasound revealed a SAW obstructing the flow of cerebrospinal fluid (CSF). The left and right sides of the posterior space were divided by the septum posticum, which moved pulsatile from side to side. Postoperative improvements in muscle strength, temperature, and pain sensation were observed; however, numbness and bladder dysfunction persisted. Diagnosing SAW is challenging in the absence of the scalpel sign; however, in cases of spinal cord atrophy and a dorsal CSF flow void on MRI, the presence of SAW should be considered. Brown-Sequard syndrome may result from asymmetric CSF pressure caused by the septum posticum.