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Diagnosis and treatment of noncommunicating extradural spinal thoracolumbar arachnoid cyst
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How to cite this article: Khan SI, Ahmed N, Chaurasia B, Ahsan K. Diagnosis and treatment of noncommunicating extradural spinal thoracolumbar arachnoid cyst. Surg Neurol Int 2020;11:405.
Abstract
Background:
Noncommunicating extradural spinal arachnoid cysts are extremely rare. They are believed to arise from congenital defects in the dura mater and become enlarged as a consequence of increased cerebro-spinal fluid (CSF) pressure within the subarachnoid space. Most retain a communicating pedicle through which the extradural cyst maintains connection with the subarachnoid space, and only rarely does this communication become sealed. The optimal treatment consists of complete surgical removal of the cyst with ligation of the communicating pedicle.
Case Description:
A 29-year-old male presented with a progressive spastic paraparesis of 6 months’ duration. The MRI showed a circumscribed intradural extramedullary cystic lesion located from D11-L2. Notably, peroperatively, the cyst appeared to be entirely extradural, without a communicating intradural pedicle. Further, no CSF leak was observed even after Valsalva maneuvers. Following surgical extirpation of the cyst, the patient sustained an uneventful recovery within 1 postoperative month.
Conclusion:
Noncommunicating extradural arachnoid cysts are extremely rare causes of spinal cord compression and should be fully excised.
Keywords
Cerebro-spinal fluid
Noncommunicating extradural spinal arachnoid cyst
INTRODUCTION
Noncommunicating spinal extradural arachnoid cysts are extremely rare contributors to spinal cord compression and most typically involve thoracic spine (65%).[2,4] They typically develop when the arachnoid herniates through small dural defect and progressively enlarges following raised cerebro-spinal fluid (CSF) pressures. This increased wall tension causes back pressure which may contribute to the closure of the communicating pedicle[4,7] [Figure 1]. Magnetic resonance imaging is the diagnostic modality of choice, although computed tomography myelography is superior in detecting the specific location of the dural defect (e.g., communication between the cyst and the subarachnoid space).[3] Complete surgical excision with repair of the dural defect, either primarily or utilizing a duraplasty, is the treatment of choice.[1,5,6] Here, we reviewed the clinical presentation, pathogenesis, neuroimaging features, and surgical management of a noncommunicating spinal extradural arachnoid cyst.
CASE REPORT
History and physical examination
A 29-year-old male patient presented with 6 months’ duration of a progressive paraparesis (4/5) accompanied by a partial T8 sensory level, but with intact sphincter function.
Neuroimaging findings
The thoracic MR revealed a well-defined, nonenhancing intradural extramedullary cystic lesion in the spinal canal measuring 8 cm × 3.2 cm extending from D11 to L2. It was hypointense on T1 and hyperintense on T2WI studies and contained internal septations. The lesion significantly compressed the spinal cord, conus, and cauda equina [Figures 2a-c and 3a and b].
Surgery: A laminectomy was performed from D11 to L2. Once the large extradural spinal arachnoid cyst was exposed, a plane was easily developed between the cyst and thecal sac allowing for complete en bloc cyst removal [Figure 4a and b]. There was no communication with the subarachnoid space as confirmed utilizing multiple Valsalva maneuvers. Due to the extensive laminectomy at the thoracolumbar junction and the anticipation of instability, the patient then underwent pedicle screw/rod fixation with posterolateral fusion using autologous bone chips from D11 to L2. Within 1 postoperative month, there was complete resolution of the preoperative motor deficit (e.g., with subsidence of the preoperative T8-level tingling, numbness, and resolution of weakness). Histopathologically, the lesion was an arachnoid cyst.
DISCUSSION
Noncommunicating spinal extradural arachnoid cysts are extremely rare. The pathophysiology of cyst enlargement can be explained by either the active fluid secretion theory or pulsatile CSF dynamic theory.[6]
They have been classified into three categories: extradural cysts without spinal nerve root fibers (Type I), subdivided into extradural arachnoid cysts (Type IA), sacral meningoceles (Type IB), extradural cysts with spinal nerve root fibers (Type II), and intradural cysts (Type III).[1]
Clinical presentation
These cysts are usually seen in adolescents, whereas dorsolumbar and lumbar cysts usually appear in adults. Single cysts can extend over several spinal segments in craniocaudal direction, and may be accompanied by multiple, separate dural defects/communicating pedicles.[8] Neurological deficits depend on the location of the cyst and extent of compression and/or compromise of neurovascular structures.[5]
Diagnostic studies of choice for spinal arachnoid cysts
MR is the diagnostic study of choice because as it best defines the type and extent of the cyst, and relationship to surrounding neurovascular structures. For demonstrating the communication with the subarachnoid space, the optimal examination is the CT myelogram.[3]
CONCLUSION
Noncommunicating extradural thoracic spinal arachnoid cysts rarely contribute to spinal cord compression as shown in the case presented. The treatment of choice is routine gross total resection utilizing a decompressive laminectomy alone, with only select cases warranting consideration of fusion.
Acknowledgment
We are grateful to Dr. Nazmin Ahmed for the wonderful color illustrations.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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