Diagnostic Performance of Renal Contrast Excretion on Early-Phase CT Myelography in Spontaneous Intracranial Hypotension

Background and purpose: Early opacification of the renal collecting system during CT myelography (CTM) performed for the evaluation of spontaneous intracranial hypotension (SIH) has been demonstrated in prior studies. However, these investigations often included CTMs scanned >30 minutes after intrathecal contrast injection, a longer delay than the myelographic techniques used in current practice. The purpose of this study was to determine whether renal contrast excretion (RCE) measured during this earlier time period (≤30 minutes) can discriminate patients with SIH from patients without SIH.

Materials and methods: A single-center, retrospective cohort of consecutive patients presenting for evaluation of possible SIH between July 2021 and May 2022 was studied. RCE was measured in both renal hila by using standardized (5-15 mm³) ROIs. Receiver operating characteristic (ROC) curves were constructed by comparing RCE between patients with SIH and patients without SIH in the overall cohort and within the subgroup of patients with negative myelograms.

Results: The study cohort included 190 subjects. Both unadjusted and adjusted models demonstrated a statistically significant increase in renal contrast attenuation among patients with SIH compared with those without SIH (P values ≤.001). The ROC curve showed moderate discrimination between these groups (area under the ROC curves [AUC] 0.76). However, by using clinically meaningful test criteria of sensitivity >90% or specificity >90%, the 2 corresponding threshold hounsfield units (HU) values resulted in low specificity of 31.3% and sensitivity of 50.8%. Subgroup analysis of patients with negative myelograms showed poorer performance in discriminating SIH+ from SIH- (AUC 0.62). In this subgroup, using similar test criteria of sensitivity >90% or specificity >90 resulted in low specificities and sensitivities, at 26.0% and 37.5%, respectively.

Conclusions: We found a statistically significant positive association between RCE and SIH diagnosis during early-phase CTM; however, clinically useful thresholds based on cutoff values for renal HU resulted in poor sensitivities or specificities, with substantial false-positives or false-negatives, respectively. Thus, while we confirmed statistically significant differences in RCE in the ≤30-minute period, in keeping with prior investigations of more delayed time periods, overlap in renal attenuation values prevented the development of clinically useful threshold values for discriminating SIH+ from SIH- patients.