Abstract 284: Renal Contrast Excretion After Myelography: A Valuable Tool in The Diagnosis of Cerebrospinal‐Venous Fistulae
Authors: Bounni Firas , Patel Neil V. , Orru Emanuele 
Published: March 2024

Introduction
Cerebrospinal‐venous fistulae (CSF‐VFs) represent a pathologic, low‐flow direct connection between the intrathecal space, usually at the level of a diverticular dilation of a nerve root sleeve, and the thoracolumbar venous system. They can cause CSF hypovolemia resulting in an often‐debilitating intracranial hypotension syndrome. Lateral decubitus CT or DSA myelography (CTM, DSM) are the gold‐standard modalities for diagnosing these entities. Their high spatial and temporal resolution allows visualization of the abnormal connection between the two spaces. Yet, the small size and low flow make CSF‐VFs radiographically subtle, and may not be consistently visualized even after a correctly‐performed CTM/DSM, requiring repeated invasive procedures to definitively establish or exclude their presence. Opacification of the renal excretory system 30‐60 minutes after lateral decubitus myelograms is thought to be a highly sensitive and specific indirect sign of the presence of a CSF‐VF 1,2, as this amount of time is considered insufficient to allow arachnoid reabsorption of contrast. Renal pelvises hyperdensity or its absence after a negative decubitus CTM/DSM can prompt further myelographic investigation or definitively rule out the presence of a CSF‐VF on the side of the examination, respectively.

Methods
We present three patients with severely symptomatic CSF‐VFs treated at our hospital between 2021 and 2023. All patients were females (range: 50‐60 years old). All three patients underwent bilateral diagnostic lateral decubitus DSM/CTM. Exams were performed at least 72 hours apart in order to allow complete clearance of intrathecal contrast. After each myelographic acquisition, patients remained in the lateral decubitus position until abdominal CT imaging was performed at 30 and 45 minutes to detect the presence of contrast in the renal collecting system.

Results
Patients 1 and 2, had a CSF‐VF between nerve root dural diverticula and the azygos system that was directly visualized on lateral decubitus CTM (patient 1: right T10‐T11, patient 2: left T8‐T9). Contrast was detectable in the renal pelvises after myelography was performed on the affected side, and not detectable after the contralateral investigation. One fistula was treated via CT‐guided targeted blood patch and fibrin glue injection and the other via endovascular Onyx embolization of the tributary Intercostal veins.
Patient 3 had an extremely slow flow CSF‐VF at the right T11‐12 level that was identified only after 5 right‐sided decubitus myelograms with both modalities. The repeated exams were based on the presence of contrast in the renal pelvises after each right‐sided procedure and on the absence of renal opacification after the left‐sided myelograms. Eventually, a CSF‐VF was identified. Successful Onyx embolization of the foraminal veins of the R T11‐12 levels was performed.
All three patients had complete resolution of symptoms.

Conclusion
Contrast presence in the renal excretory system after a lateral decubitus CTM/DSM is a potentially highly sensitive and specific indirect diagnostic sign that can establish or exclude the presence of a CSF‐VF on the examined side. It could be particularly helpful when the fistula is not initially detected, as it can prompt aggressive continuation of the myelographic work‐up. Similarly, it can exclude its presence on one side, sparing the patient invasive and low yield diagnostic procedures.