The clue is in the kidneys: greater renal contrast medium accumulation on ipsilateral side down CT myelogram after lateral decubitus digital subtraction myelogram as a predictor of laterality of cerebrospinal fluid leak

AIM: To assess the potential correlation of the laterality of a cerebrospinal fluid (CSF)–venous fistula with the laterality of decubitus computed tomography (CT) myelogram (post decubitus digital subtraction myelogram) based on which side demonstrated more renal contrast medium excretion. MATERIALS AND METHODS: Patients with CSF–venous fistulas diagnosed at lateral decubitus digital subtraction myelograms were reviewed retrospectively. Patients who did not have CT myelogram following one or both left and right lateral decubitus digital subtraction myelograms were excluded. Two neuroradiologists independently interpreted the CT myelogram for the presence or absence of renal contrast, and whether subjectively more renal contrast medium was visualised on the left or right lateral decubitus CT myelogram. RESULTS: Renal contrast medium was seen in lateral decubitus CT myelograms in 28 of 30 (93.3%) patients with CSF–venous fistulas. Having more renal contrast medium in right lateral decubitus CT myelogram was 73.9% sensitive and 71.4% specific for the diagnosis of a right-sided CSF–venous fistula, whereas having more renal contrast medium in the left lateral decubitus CT myelogram was 71.4% sensitive and 82.6% specific for a left-sided CSF–venous fistula (p=0.02). CONCLUSION: When the CSF–venous fistula lies on the dependent side of a decubitus CT myelogram performed after decubitus digital subtraction myelogram, relatively more renal contrast medium is visualised compared to when the fistula lies on the non-dependent side.