Transverse dorsal arachnoid web and syringomyelia: case report

We present a case of syringomyelia attributed to a transverse thoracic arachnoid web at T4. The cerebrospinal fluid pressure caudal to the web was higher than the cerebrospinal fluid pressure rostral to the web, causing a syrinx in the thoracic and cervical spinal cord above the web.

A 43-year-old man presented with numbness and a burning pain in his left upper back and extremities. Magnetic resonance imaging showed a cervical-thoracic syrinx that terminated relatively abruptly at T4. Because of the abrupt termination of the syrinx at T4 and the slight ventral displacement of the spinal cord at this level, a dorsal arachnoid web was suspected.

A T4 laminectomy was performed. Intraoperative ultrasound before opening of the thecal sac showed a pulsating transverse dorsal arachnoid web. The dura was opened and the web resected, thus widely communicating the dorsal subarachnoid space. The syrinx dramatically decreased in size and the patient's pain improved but did not resolve completely.

In patients with presumed idiopathic syringomyelia, imaging studies should be closely inspected for the presence of a transverse arachnoid web. Surgical resection of a transverse thoracic arachnoid web with syringomyelia can result in resolution of the syringomyelia and improvement in neurological function. Syrinx formation in patients with these webs may occur in the area of the spinal cord where there is lower cerebrospinal fluid pressure, which may be either rostral or caudal to the arachnoid web. We evaluate this hypothesis by comparing our case with other published cases.