"Empty Cyst Sign" Appearance of CSF-Venous Fistula on Digital Spinal Myelography

Cerebrospinal fluid venous fistulas (CSF-VFs) are an uncommon, yet increasingly recognized, cause of spontaneous intracranial hypotension.^1-5 The workup involves magnetic resonance imaging (MRI) of the brain with and without contrast and MRI of the neuroaxis without contrast before dynamic myelography, either computed tomography or digital subtraction.⁶ The present case of an older woman with symptomatic intracranial hypotension is notable for the specific appearance of CSF-VFs on digital spinal myelography (Video 1). Among her numerous perineural cysts, it was the "disappearing" or "empty" cyst from which the fistula originated. The diagnosis was made using a second lateral fluoroscopy view, not typically used in digital spinal myelography, which demonstrated emptying of contrast from the T6 perineural cyst into the segmental vein at this level, or the "empty cyst sign." The patient then underwent transvenous onyx embolization with resolution of her orthostatic headaches and improvement of contrast-enhanced MRI of the brain with the Bern score decreasing from 7 to 0 at 3 months of follow-up.⁷ Because transvenous embolization of CSF-VFs is a relatively new procedure, the long-term outcomes of the procedure are not yet known.