Spinal arachnoid web-a review article

Abstract

The spinal arachnoid web is an abnormal formation of an arachnoid membrane in the subarachnoid space. It is a rare entity with some degree of uncertainty surrounding its etiology. It can result in a displacement of the spinal cord causing pain and neurological symptoms as well as blockage of cerebrospinal fluid (CSF) flow and subsequent syringomyelia. The syrinx resulting from the altered CSF flow dynamics has been described to assume variable positions relative to the web itself. The "scalpel sign" is regarded as a pathognomonic feature of a spinal arachnoid web. The arachnoid web, however, is relatively thin and may be elusive of routine radiological investigations. As such, a myriad of preoperative and intraoperative investigations have been postulated to improve the sensitivity of detecting this abnormality. Management of spinal arachnoid webs ranges from conservative management to surgical excision where in the latter, the extent of excision remains the subject of debate. The authors herein present a review of the available information on this rare topic.

Keywords: Spinal arachnoid web (SAW); Venturi effect; dorsal arachnoid web (DAW); scalpel sign; spinal arachnoid cysts (SAC); syringomyelia.

Figure 1

MRI T2-weighted images showing: pre-operative sagittal (A) and axial (B) scans demonstrating T6 anterior wedge fracture (*), transverse hypointense lesion at T3 (arachnoid web), 2-cm hypointense signal at T3–T4 with dorsal spinal cord indentation and anterior cord displacement “Scalpel sign” (long arrow) with increased cord signal at this level (short arrow); post-operative sagittal (C) and axial (D) scans showing relief of the dorsal cord compression post-laminectomy and excision/fenestration of the arachnoid web.

Figure 2

MRI T2WI showing: (A,B) small focal syrinx within the cord at the C6 level (long arrows); (C,D) focal anterior displacement of the dorsal cord at the T3 level highly suggestive of an arachnoid web (short arrow). T2WI, T2-weighted image.