Decubitus Myelography for Spinal Extradural Arachnoid Cyst-Better Classified as a Lateral Dural CSF Leak?

Spinal extradural arachnoid cysts are rare lesions that may result in compressive myelopathy. Their etiology is unclear, but they are thought to represent extradural collections due to a one-way dural defect from the subarachnoid space to the cyst. To date, identifying this dural defect on MRI and myelography have had limited and variable success. Surgery is the standard treatment for these cysts; however, there is debate whether total cyst removal is necessary versus dural repair alone. In this technical report, we show how dynamic decubitus CT and digital subtraction myelography can identify the dural defect and precisely guide the surgical approach. We also discuss many similarities between spinal extradural arachnoid cysts and lateral dural tear CSF leaks observed in patients with spontaneous intracranial hypotension and suggest they may represent a spectrum of CSF leaks.ABBREVIATIONS: SIH ＝ spontaneous intracranial hypotension; CTM ＝ CT myelography; DSM = digital subtraction myelography.