Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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April 26, 2018
Spinal Arachnoid Cyst with Intramedullary Extension
- Background:
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Spinal arachnoid cysts may be intradural or extradural.
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Most intradural spinal arachnoid cysts are found in the posterior subarachnoid space and arise from the septum posticum, which is a thin membranous partition that divides the posterior subarachnoid space longitudinally.
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Intramedullary arachnoid cysts are rare, with only a few cases reported.
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- Clinical Presentation:
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Most spinal arachnoid cysts are asymptomatic and are detected incidentally.
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Symptoms are due to spinal cord compression and are typically pain and progressive spastic or flaccid paraparesis, which are often exacerbated by Valsalva maneuvers.
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Isolated radiculopathy, noncardiac chest pain, isolated gait difficulty, and isolated urinary urgency are less common presenting symptoms.
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- Key Diagnostic Features:
- Intramedullary nonenhancing cystic lesion following the CSF signal on all sequences, with displacement of the spinal cord
- Absence of CSF related flow voids within the lesion
- Cine flow MRI may demonstrate cyst communication with the subarachnoid space and absent CSF flow within the cyst.
- Histopathology in this case from sections from the "D1–4 arachnoid cyst" showed a thick fibrocollagenous wall with arachnoidal cell lining. Sections examined from "D5–7 intramedullary extension" showed white matter with occasional terminal nerve branches and thickened arachnoid, consistent with an arachnoid cyst.
- Differential Diagnoses:
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Hydatid cyst: usually multiloculated and centered in the bone
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Spinal cysticercosis: shows peripheral enhancement
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Epidermoid cyst: bright on DWI
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Dermoid cyst: has fat signal content
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Ventral cord herniation: focal deformity along the ventral aspect of the cord due to herniation through a ventral dural defect
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Arachnoid web: focal dorsal indentation on the cord, described as the “scalpel sign”
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Absence of well-defined walls
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Arachnoid cyst produces a wide indentation and has perceptible walls.
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- Treatment:
- Symptomatic cysts are surgically resected.
- If complete resection is impossible, fenestration of the cyst wall, drainage, or shunting may be done to relieve symptoms.
- Asymptomatic cysts are followed up yearly.
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