Arachnoid Web Fenestration: Diagnostic and Surgical Nuances

Arachnoid web (AW) is a rare phenomenon that has only been described in small case reports and case series,¹ most commonly presenting with upper motor neuron signs and subtle radiographic findings, such as the classically described “scalpel sign.”² In this report, we demonstrate the use of imaging and operative techniques that have not been previously shown in the literature as a video for AW. These include high-definition magnetic resonance imaging (MRI) sequences for preoperative diagnosis, use of intraoperative ultrasonography for identification of adhesions, and operative technique for AW fenestration (Video 1). The patient consented to this manuscript. A 64-year-old female patient developed progressive difficulty with balance and ambulation that particularly worsened over the last 4 months associated with tingling and numbness in the bilateral lower extremities. Physical examination revealed spastic gait and upper motor neuron signs in the lower extremities along with left foot drop. MRI revealed a chronic noncontrast-enhancing intramedullary lesion, along with a spinal cord indentation at the level T6 with an associated fiber between the cord and the posterior dura. Surgical intervention was performed with the use of intraoperative fluoroscopy and ultrasound for real-time identification of the surgical site and the AW. Under the microscope, the dura was incised while preserving the arachnoid. The AW was carefully dissected, leaving the portions that were tethered onto the cord. Two weeks postoperatively, the patient's gait was markedly improved, with resolved neurologic function in the lower extremities. Follow-up MRI at 3 months demonstrated resolved medullary syrinx and normalization of the spinal cord contour.