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| LETTERS TO EDITOR |
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| Year : 2018 | Volume
: 66
| Issue : 6 | Page : 1839-1841 |
Dorsal arachnoid web: A missed entity
Priyamvadha Kovai1, Paramveer Sabharwal2, Anil K Singh1
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 Publication | 28-Nov-2018 |
Correspondence Address:
Dr. Priyamvadha Kovai
Department of Neurosurgery, Max Institute of Neurosciences, Malsi, Dehradun - 248 001, Uttarakhand
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0028-3886.246271
How to cite this article:
Kovai P, Sabharwal P, Singh AK. Dorsal arachnoid web: A missed entity. Neurol India 2018;66:1839-41 |
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 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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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 | |  |
| 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.  |
| 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. |
| 3. | Jayabal J, Nilsson C, Muthu T, Chung KK. Mystery Case: Scalpel sign: Dorsal thoracic arachnoid web. Neurology 2015;85:e150-1. |
| 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. |
| 5. | Sridharan A, Heilman CB. Transverse dorsal arachnoid web and syringomyelia: Case report. J Neurosurg 2009;65:E216-7. |
| 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. |
| 7. | Brodbelt AR, Stoodley MA. Syringomyelia and the arachnoid web. Acta Neurochir (Wien) 2003;145:707-11. |
| 8. | McCormick PC. Dorsal arachnoid web. Neurosurg Focus 2014;37 Suppl 2:Video 8. doi: 10.3171/2014.V3.FOCUS14273. |
| 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. [ PUBMED] [Full text] |
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1]
| This article has been cited by | | 1 |
Spinal arachnoid web—a distinct entity of focal arachnopathy with favorable long-term outcome after surgical resection. Analysis of a multicenter patient population |
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| Stefanos Voglis, Alexander Romagna, Menno R. Germans, Isaac Carreno, Martin N. Stienen, Anna Henzi, Katrin Frauenknecht, Elisabeth Rushing, Granit Molliqaj, Kayee Tung, Enrico Tessitore, Howard J. Ginsberg, David Bellut | | The Spine Journal. 2021; | | [Pubmed] | [DOI] | | | 2 |
Neuroimaging findings and pathophysiology of dorsal spinal arachnoid webs: illustrative case |
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| Nancy Pham, Julius O. Ebinu, Tejas Karnati, Lotfi Hacein-Bey | | Journal of Neurosurgery: Case Lessons. 2021; 1(20) | | [Pubmed] | [DOI] | |
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