Surgical Release of a Dorsal Thoracic Arachnoid Web

Dorsal arachnoid web (DAW) is a rare clinical entity with unknown etiology, and it can mimic other conditions on imaging.^1,2 We present a surgical video of a patient with DAW that was misdiagnosed as ventral cord herniation. A 35-year-old woman presented with upper back pain and progressive bilateral lower extremity weakness and numbness for a few months. Magnetic resonance imaging (MRI) of the thoracic spine (T) showed ventral cord displacement with a syrinx that extended from T2-4. The computed tomography myelogram showed no contrast anterior to the spinal cord. The patient underwent T3-5 laminectomy. Intraoperatively, we found a thoracic DAW and cord displacement with no herniation (Video 1). We performed adhesiolysis to restore the cerebrospinal fluid circulation. On 4-month follow-up, the patient examination had demonstrated progressive improvement of her previous symptoms (weakness, numbness, and urinary retention), and the repeat MRI scan showed a significant reduction in the size of the syrinx. DAW can mimic other pathologies on preoperative imaging, such as ventral cord herniation and arachnoid cyst. The presence of "scalpel sign" and a syrinx on MRI with no arachnoid cyst on myelography support the diagnosis of DAW.