Electrodiagnostic and Advanced Neuroimaging Characterization for Successful Treatment of Spinal Extradural Arachnoid Cyst

Background: Spinal extradural arachnoid cysts are relatively uncommon. Rarely, large cysts presented with spinal cord compression requiring surgical intervention.

Case description: We report a patient with a progressively enlarging spinal extradural arachnoid cyst causing worsening right S1 radiculopathy and gastrocnemius muscle atrophy. Electromyography and nerve conduction studies revealed an S1 motor radiculopathy. Serial magnetic resonance imaging findings confirmed enlargement of the small cyst originating from the sacral thecal sac on the right while 2 smaller cysts on the left remained stable. Dynamic computed tomography myelogram revealed connection to the thecal sac behind the right S1 nerve root. We performed a right hemilaminectomy from L5 to S2, exposed the cyst pedicle ligated it, and marsupialized the cyst. After surgery, the patient showed clinical and electrodiagnostic improvement.

Conclusion: This case illustrates the principles of timely surgical intervention after advanced diagnostic imaging and electrodiagnostic testing to improve neurologic function and minimize complications.