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|LETTERS TO EDITOR
|Year : 2018 | Volume
| 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|
Dr. Priyamvadha Kovai
Department of Neurosurgery, Max Institute of Neurosciences, Malsi, Dehradun - 248 001, Uttarakhand
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kovai P, Sabharwal P, Singh AK. Dorsal arachnoid web: A missed entity. Neurol India 2018;66:1839-41
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. 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].,,,,,,,,
|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. 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. 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.,,,,, 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.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]