来源：jxradiology
男，66岁，间歇性双下肢疲软和麻木、行走困难
图片说明：
Sagittal T2WI (A) and CT myelogram (C) show focal indentation on the dorsal surface of the thoracic spinal cord, giving the “scalpel sign” (arrows). Axial T2WI above the level of the indentation (B) shows increased signal within the cord. CT myelogram at the level of the indentation (C, D) shows smooth ventral surface of the cord and opacification of the widened CSF space dorsally.
诊断：胸髓背侧蛛网膜网带
Dorsal Thoracic Arachnoid Web
Background:
Arachnoid webs are intradural extramedullary transverse bands causing indentation on the dorsal surface of the spinal cord, with predilection for the upper thoracic spine.
Clinical Presentation:
Upper and lower extremity weakness, numbness and back pain
Key Diagnostic Features:
Focal dorsal indentation of the spinal cord, the “scalpel sign” (scalpel with the blade pointing dorsally).
The ventral surface of the cord is not deformed.
The widened CSF space posterior to the cord opacifies with contrast on myelographic studies. The spinal cord adjacent to the web may show increased T2 signal which may progress to syrinx formation.
Differential Diagnosis:
Spinal cord herniation: Deformity of the ventral cord surface with cord protrusion through anterior dural defect
Intraspinal dorsal arachnoid cyst: Smooth scalloping of the cord with no or delayed opacification on myelography
Treatment:
Surgical lysis of the web
Suggested Reading
Reardon MA, Raghavan P, Carpenter-Bailey K, et al. Dorsal thoracic arachnoid qeb and the “scalpel sign”: a distinct clinical-radiologic entity. AJNR Am J Neuroradiol 2013;34:1104–10, 10.3174/ajnr.A3432
Sridharan A, Heilman C. Transverse dorsal arachnoid web and syringomyelia: case report.Neurosurgery 2009;65:e216–17, 10.1227/01.NEU.0000348007.84175.FA
下图是另一例（ AJNR 2013 34: 1104-1110）胸髓背侧蛛网膜网带（dorsal thoracic arachnoid web）患者，CT脊髓造影所示的典型“手术刀征（scalpel sign）”：
患者的MRI、术中及蛛网膜网带切除术后照片；在T5-9椎板切除术中，切开后部硬脊膜后，所示解剖结构见下图D。术中切除异常病灶后，所示胸髓见下图E。此外，术中还对前部硬脊膜进行了探查，未发现腹侧硬脊膜缺损（ventral dural defect），也未发现腹侧脊髓疝（ventral spinal cord herniation）。
讨论
背侧蛛网膜网带（dorsal arachnoid web）几乎均发生于上段及中段胸髓。该病可以导致脊髓压迫症，并继发脊髓空洞症，（但并非总是会导致脊髓空洞形成）；脊髓空洞既可以发生于胸髓受压平面的上方，也可以发生于胸髓受压平面的下方。该病虽较为罕见，但有三点值得注意：
1.“手术刀征（scalpel sign）”是该病的诊断提示性影像学特点；
2.该病是脊髓压迫症、脊髓空洞症的一个重要病因；
3.经影像学表现考虑到该病的诊断，并经手术切除异常的蛛网膜网带（arachnoid web）、解除压迫后，患者的症状体征甚至此前的脊髓空洞均可明显改善。
文献里解释说，是蛛网膜band，蛛网膜束带，因此，国内文献一般翻译为“蛛网膜网带（arachnoid web）。
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