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296 January-February 2015
radiographics.rsna.org
Dorsal Thoracic Arachnoid Web: Another Intradural Entity with Ventral Cord Displacement From: Sugoto Mukherjee, MD, Michael A. Reardon, MD, Department of Radiology and Medical Imaging, University of Virginia Health System, PO Box 800170, Charlottesville, VA 22908-0170 Prashant Raghavan, MD, Department of Diagnostic Radiology and Nuclear Medicine, University of Maryland School of Medicine, Baltimore, Md e-mail: [email protected]
Editor: We found the article by Haber et al (1) in the March-April 2014 issue of RadioGraphics to be an informative and excellent review of cerebrospinal fluid–isointense lesions with mass effect (displacement) of the spinal cord. However, we want to bring attention to an entity that has similar imaging features to the intradural arachnoid cysts shown in Figure 3 in the article by Haber et al (1). We recently published a report on a series of cases of dorsal thoracic arachnoid web that manifested at imaging with a pathognomonic “scalpel” sign (2), a characteristic dorsal focal indentation seen on computed tomographic (CT) myelograms and sagittal magnetic resonance (MR) images (Figure). At T2-weighted MR imaging, 10 of the 14 patients showed increased signal intensity in the spinal cord or syringomyelia, with surgical confirmation of an arachnoid web in all five patients who underwent surgery. The etiology of these webs is unknown. Only five of the 14 patients reported a history of trauma or surgery. Although it is conceivable that the imaging findings represent collapsed, incomplete, or disrupted arachnoid
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Figure. (a, b) Preoperative sagittal CT myelo-
gram (a) and sagittal T2-weighted MR image (b) show a pathognomonic dorsal indentation (arrow), with anterior displacement of the upper thoracic spinal cord. The finding resembles a scalpel with its blade directed posteriorly (the “scalpel” sign). In b, note also the increased spinal cord signal intensity and syringomyelia above the level of the indentation. (c) Sagittal T2-weighted MR image obtained after laminectomy and resection of a posterior arachnoid web shows resolution of the dorsal indentation, spinal cord signal abnormality, and syringomyelia.
cysts, it is possible that these lesions are primarily webs of thickened arachnoid membrane. More important, there is a definite relationship between dorsal arachnoid webs and changes in spinal cord signal intensity, given the reversal or reduction of intramedullary signal intensity seen at follow-up MR imaging in most of our patients (Figure). As mentioned in the article by Haber et al (1), spinal cord herniation can be distinguished from dorsal arachnoid webs and intradural arachnoid cysts in most cases. Radiologists should recognize and alert the surgeon to this distinctive finding to avoid delayed treatment as well as unnecessary intervention (ie, cord biopsy
or shunt placement) because surgical lysis of the web is curative. Since the publication of our case series, we have encountered additional similar cases that have demonstrated postoperative resolution of the spinal cord deformity and signal abnormality, with symptom improvement.
References 1. Haber MD, Nguyen DD, Li S. Differentiation of idiopathic spinal cord herniation from CSF-isointense intraspinal extramedullary lesions displacing the cord. RadioGraphics 2014;34(2):313–329. 2. Reardon MA, Raghavan P, Carpenter-Bailey K, et al. Dorsal thoracic arachnoid web and the “scalpel sign”: a distinct clinical-radiologic entity. AJNR Am J Neuroradiol 2013;34 (5):1104–1110.
296 January-February 2015
radiographics.rsna.org
Dorsal Thoracic Arachnoid Web: Another Intradural Entity with Ventral Cord Displacement From: Sugoto Mukherjee, MD, Michael A. Reardon, MD, Department of Radiology and Medical Imaging, University of Virginia Health System, PO Box 800170, Charlottesville, VA 22908-0170 Prashant Raghavan, MD, Department of Diagnostic Radiology and Nuclear Medicine, University of Maryland School of Medicine, Baltimore, Md e-mail: [email protected]
Editor: We found the article by Haber et al (1) in the March-April 2014 issue of RadioGraphics to be an informative and excellent review of cerebrospinal fluid–isointense lesions with mass effect (displacement) of the spinal cord. However, we want to bring attention to an entity that has similar imaging features to the intradural arachnoid cysts shown in Figure 3 in the article by Haber et al (1). We recently published a report on a series of cases of dorsal thoracic arachnoid web that manifested at imaging with a pathognomonic “scalpel” sign (2), a characteristic dorsal focal indentation seen on computed tomographic (CT) myelograms and sagittal magnetic resonance (MR) images (Figure). At T2-weighted MR imaging, 10 of the 14 patients showed increased signal intensity in the spinal cord or syringomyelia, with surgical confirmation of an arachnoid web in all five patients who underwent surgery. The etiology of these webs is unknown. Only five of the 14 patients reported a history of trauma or surgery. Although it is conceivable that the imaging findings represent collapsed, incomplete, or disrupted arachnoid
RG • Volume 35 Number 1
Courcoutsakis and Mukherjee 297
Figure. (a, b) Preoperative sagittal CT myelo-
gram (a) and sagittal T2-weighted MR image (b) show a pathognomonic dorsal indentation (arrow), with anterior displacement of the upper thoracic spinal cord. The finding resembles a scalpel with its blade directed posteriorly (the “scalpel” sign). In b, note also the increased spinal cord signal intensity and syringomyelia above the level of the indentation. (c) Sagittal T2-weighted MR image obtained after laminectomy and resection of a posterior arachnoid web shows resolution of the dorsal indentation, spinal cord signal abnormality, and syringomyelia.
cysts, it is possible that these lesions are primarily webs of thickened arachnoid membrane. More important, there is a definite relationship between dorsal arachnoid webs and changes in spinal cord signal intensity, given the reversal or reduction of intramedullary signal intensity seen at follow-up MR imaging in most of our patients (Figure). As mentioned in the article by Haber et al (1), spinal cord herniation can be distinguished from dorsal arachnoid webs and intradural arachnoid cysts in most cases. Radiologists should recognize and alert the surgeon to this distinctive finding to avoid delayed treatment as well as unnecessary intervention (ie, cord biopsy
or shunt placement) because surgical lysis of the web is curative. Since the publication of our case series, we have encountered additional similar cases that have demonstrated postoperative resolution of the spinal cord deformity and signal abnormality, with symptom improvement.
References 1. Haber MD, Nguyen DD, Li S. Differentiation of idiopathic spinal cord herniation from CSF-isointense intraspinal extramedullary lesions displacing the cord. RadioGraphics 2014;34(2):313–329. 2. Reardon MA, Raghavan P, Carpenter-Bailey K, et al. Dorsal thoracic arachnoid web and the “scalpel sign”: a distinct clinical-radiologic entity. AJNR Am J Neuroradiol 2013;34 (5):1104–1110.
