Dorsal Thoracic Arachnoid Web and the “Scalpel Sign”: A Distinct Clinical-Radiologic Entity

Abstract

SUMMARY:Arachnoid webs are intradural extramedullary bands of arachnoid tissue that can extend to the pial surface of the spinal cord, causing a focal dorsal indentation of the cord. These webs tend to occur in the upper thoracic spine and may produce a characteristic deformity of the cord that we term the "scalpel sign." We describe 14 patients whose imaging studies demonstrated the scalpel sign. Ten of 13 patients who underwent MR imaging demonstrated T2WI cord signal-intensity changes, and 7 of these patients also demonstrated syringomyelia adjacent to the level of indentation. Seven patients underwent surgery, with 5 demonstrating an arachnoid web as the cause of the dorsal indentation demonstrated on preoperative imaging. Although the webs themselves are rarely demonstrated on imaging, we propose that the scalpel sign is a reliable indicator of their presence and should prompt consideration of surgical lysis, which is potentially curative. S

Surgical management of syringomyelia unrelated to Chiari malformation or spinal cord injury

“…Sagittal and axial T2-weighted MR images can now be correlated with cardiac-gated 2D phase contrast, which is the method of choice to detect CSF flow abnormalities. Specifically, subtle arachnoid scarring may be indirect evidence for cord deformity or focal blurring of the syrinx wall, as well as direct evidence for an arachnoid web or cyst, obtained using 1.5T MR or 3T MR or 3D constructive interference in steady state (CISS) sequences, in order of power of resolution and sensibility [34][35][36][37]. CSF flow void signs over the cardiac cycle (cine MR) give a dynamic picture showing a short period of cranial flow (diastolic phase) followed by a sustained period of caudal flow (systolic phase), which can be altered by CSF obstruction, being of particular significance at the craniovertebral junction [38,39].…”

“…Imaging clearly shows the degree of cord deformity and constriction proximal to the syrinx, which is an additional factor in inflammatory-driven ischemia in determining spinal damage [37]. This role can be indirectly assumed as one of the explanations for even short-term poor clinical outcome of drainage which collapses the syrinx while leaving the cord constriction untouched [18,31].…”

Unusual case of progressive myelopathy

“…Dorsal thoracic arachnoid webs are intradural extramedullary bands of arachnoid tissue which can cause focal indentation of the spinal cord and blockage of cerebrospinal fluid (CSF) flow [1]. They are a rare but increasingly recognised cause of syringomyelia with less than 20 cases reported in the literature [1][2][3][4][5][6][7][8]. Patients present with progressive myelopathy with an unusual predilection to the thoracic cord.…”

Visualization of regional cerebrospinal fluid flow with a dye injection technique in focal arachnoid pathologies

“…When we add the present 2 cases (Cases 1 and 3), only 13 cases of surgically confirmed DAWs have been reported. 1,[8][9][10] Regional CSF circulation of DAWs has rarely been mentioned and has not been fully understood in the past.…”

“…2,9 Thus, the presence of focal arachnoid pathologies may be only suspected from imaging findings such as deformity of the spinal cord and blockage of CSF flow. After the relevant lesion causing CSF blockage is located on MR images or CT myelograms, surgical lysis of the pathological arachnoid is indicated to release the blockage of the CSF pathway.…”