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Table of Contents    
Year : 2016  |  Volume : 64  |  Issue : 5  |  Page : 1092-1093

Scalpel sign of dorsal arachnoid web

Department of Radiology and Nuclear Medicine, Rush University Medical Center, Chicago, Illinois, USA

Date of Web Publication12-Sep-2016

Correspondence Address:
Sumeet G Dua
Department of Radiology and Nuclear Medicine, Rush University Medical Center, 1653 W Congress Pkwy Chicago - 60612, Illinois
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0028-3886.190228

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How to cite this article:
Dua SG, Jhaveri MD. Scalpel sign of dorsal arachnoid web. Neurol India 2016;64:1092-3

How to cite this URL:
Dua SG, Jhaveri MD. Scalpel sign of dorsal arachnoid web. Neurol India [serial online] 2016 [cited 2020 Jul 10];64:1092-3. Available from:

A 50-year-old female patient presented to our outpatient clinic with insidious onset of back pain and left-sided muscle spasms. She had a history of cervical spinal stenosis for which she underwent a cervical laminectomy and fusion in 2012. Clinical examination revealed asymmetric reflexes, increased on the left side, and patchy sensory loss in the left arm and leg. Magnetic resonance imaging of the cervical and thoracic spine was ordered to evaluate for canal stenosis and potential cord abnormalities. A scalpel-shaped dorsal indentation was noted on the upper thoracic spinal cord with cord edema above the level of contact [Figure 1]a and [Figure 1]b. Based on the classical imaging findings, a diagnosis of dorsal arachnoid web was rendered. The patient declined surgery and was conservatively managed.
Figure 1: (a and b) Sagittal short TI inversion recovery and T2-weighted images of the thoracic spine show a scalpel-shaped (inset in b) indentation on the upper thoracic spinal cord (arrow in a) with cord edema superiorly

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Arachnoid webs are bands of intradural arachnoid tissue that extend from the pial surface of the dorsal aspect of the spinal cord and have a predilection for involvement of the upper thoracic spine. The etiopathogenesis of arachnoid webs is uncertain, and the proposed theories describe the webs as remnants of disrupted or collapsed arachnoid cysts.[1] Back pain, lower extremity weakness, and paresthesia are the most common symptoms. On imaging, arachnoid webs produce a characteristic scalpel-shaped indentation on the dorsal aspect of the spinal cord. Their presence, therefore, is heralded by the “scalpel sign.” Intramedullary edema, a presyrinx or an acutal syrinx formation is typically seen within the indented spinal cord either above or below the level of indentation, presumably due to altered cerebrospinal fluid dynamics.[1] High-resolution T2-weighted images may occasionally show the web.[2]

Awareness of the “scalpel sign” can help in accurate identification of this elusive abnormality, and thereby accurately direct further management. Surgical treatment is curative, especially in patients with progressive symptoms.

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  References Top

Reardon MA, Raghavan P, Carpenter-Bailey K, Mukherjee S, Smith JS, Matsumoto JA, et al. Dorsal thoracic arachnoid web and the “scalpel sign”: A distinct clinical-radiological entity. AJNR Am J Neuroradiol 2013;34:1104-10.  Back to cited text no. 1
Grewal SS, Pirris SM, Vibhute PG, Gupta V. Identification of arachnoid web with a relatively novel magnetic resonance imaging technique. Spine J 2015;15:554-5.  Back to cited text no. 2


  [Figure 1]


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