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Table of Contents    
LETTERS TO EDITOR
Year : 2018  |  Volume : 66  |  Issue : 6  |  Page : 1839-1841

Dorsal arachnoid web: A missed entity


1 Department of Neurosurgery, Max Institute of Neurosciences, Malsi, Uttarakhand, India
2 Consultant in Neuroradiology and Neurointervention, Advanced Imaging Solutions, Dehradun, Uttarakhand, India

Date of Web Publication28-Nov-2018

Correspondence Address:
Dr. Priyamvadha Kovai
Department of Neurosurgery, Max Institute of Neurosciences, Malsi, Dehradun - 248 001, Uttarakhand
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.246271

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How to cite this article:
Kovai P, Sabharwal P, Singh AK. Dorsal arachnoid web: A missed entity. Neurol India 2018;66:1839-41

How to cite this URL:
Kovai P, Sabharwal P, Singh AK. Dorsal arachnoid web: A missed entity. Neurol India [serial online] 2018 [cited 2018 Dec 19];66:1839-41. Available from: http://www.neurologyindia.com/text.asp?2018/66/6/1839/246271




Sir,

A 58-year old gentleman presented with complaints of mid-back pain, radiating anteriorly to the abdomen, a band-like sensation on the upper abdomen, and difficulty in walking. Clinical examination was positive for posterior column dysfunction in the legs with dissociative anesthesia and motor weakness in the lower limbs. He was investigated with magnetic resonance imaging (MRI) of the spine, which showed the presence of a syrinx at the level of D5. Immediately caudal to the syrinx, there was a focal indentation of the spinal cord along the dorsal level [Figure 1]. Heavily-weighted T2 sequences showed the presence of a thin membrane in the subarachnoid space on the dorsal side of the cord at the same level [Figure 2]. It was hypothesized that this indentation was due to an arachnoid web and that the syrinx was due to the ingress of cerebrospinal fluid (CSF) into the spinal cord. This arachnoid web was producing the characteristic “scalpel sign” on the MRI.[1] The patient underwent a D5-6 laminectomy and excision of the arachnoid web. Care was taken to open the dura without opening the arachnoid. Just beneath the dura, a transverse band of tissue was seen compressing the cord [Figure 3]. This was the arachnoid web, which was resected, following which there was free flow of CSF. The cord was seen indented at this region, which resolved following removal of the web. The histopathology was consistent with an arachnoid web. In the immediate postoperative period, the patient had complete cessation of the mid-dorsal pain and there was also improvement in walking. An MRI of the dorsal spine was done 3 months postoperatively, which demonstrated resolution of the dorsal indentation and disappearance of the syrinx with cord expansion [Figure 4]. A brief review of published literature on dorsal arachnoid web in presented in [Table 1].[1],[2],[3],[4],[5],[6],[7],[8],[9]
Figure 1: T2-weighted images show anterior displacement of the dorsal cord which is swollen and shows cystic changes within

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Figure 2: Heavily T2-weighted three-dimensional sequence (DRIVE) shows a thin web in the dorsal subarachnoid space

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Figure 3: Intraoperative images showing the transverse arachnoid web

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Figure 4: Postoperative images show changes of laminectomy with complete resolution of the cystic myelomalacia with minimal gliosis and normalization of the cord position

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Table 1: Summary of literature review

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An arachnoid web is an abnormal formation of the arachnoid membrane in the spinal subarachnoid space that blocks the CSF flow and causes syrinx formation. It is most commonly found in the thoracic spine tenaciously attached to the dura mater and pia mater.[2] It blocks the CSF flow and causes focal compression of the spinal cord, and is a rare cause of progressive compressive myelopathy. The arachnoid web is an extramedullary transverse band of arachnoid tissue that extends to the dorsal surface of the spinal cord, resulting in mass effect and dorsal indentation, which on sagittal imaging, resembles a scalpel with its blade pointing posteriorly.[3] The syrinx is often present above or below the level of cord indentation. The definitive treatment for this condition is surgery, which involves performing a standard laminectomy with resection of the web. The dura should be opened carefully without inadvertently incising the underlying arachnoid because this helps in the intraoperative localization of the arachnoid web.[4],[5],[6],[7],[8],[9] The syrinx disappears spontaneously following resection of the web. Effective treatment of this rare condition can produce gratifying results for the patient and the clinician in the long run.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
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-radiologic entity. AJNR Am J Neuroradiol 2013;34:1104-10.  Back to cited text no. 1
    
2.
Paramore CG. Dorsal arachnoid web with spinal cord compression: Variant of an arachnoid cyst? Report of two cases. J Neurosurg 2000;93:287-90.  Back to cited text no. 2
    
3.
Jayabal J, Nilsson C, Muthu T, Chung KK. Mystery Case: Scalpel sign: Dorsal thoracic arachnoid web. Neurology 2015;85:e150-1.  Back to cited text no. 3
    
4.
Chang HS, Nagai A, Oya S, Matsui T. Dorsal spinal arachnoid web diagnosed with the quantitative measurement of cerebrospinal fluid flow on magnetic resonance imaging. J Neurosurg Spine 2014;20:227-33.  Back to cited text no. 4
    
5.
Sridharan A, Heilman CB. Transverse dorsal arachnoid web and syringomyelia: Case report. J Neurosurg 2009;65:E216-7.  Back to cited text no. 5
    
6.
Mallucci CL, Stacey RJ, Miles JB, Williams B. Idiopathic syringomyelia and the importance of occult arachnoid webs, pouches and cysts. Br J Neurosurg 1997;11:306-9.  Back to cited text no. 6
    
7.
Brodbelt AR, Stoodley MA. Syringomyelia and the arachnoid web. Acta Neurochir (Wien) 2003;145:707-11.  Back to cited text no. 7
    
8.
McCormick PC. Dorsal arachnoid web. Neurosurg Focus 2014;37 Suppl 2:Video 8. doi: 10.3171/2014.V3.FOCUS14273.  Back to cited text no. 8
    
9.
Sayal PP, Zafar A, Carroll TA. Syringomyelia secondary to “occult” dorsal arachnoid webs: Report of two cases with review of literature. J Craniovert Jun Spine 2016;7:101- 4.  Back to cited text no. 9
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