PD02-08 THE IMPORTANCE OF THE TIMING OF EXCRETORY PHASE CT SCAN IN THE DIAGNOSIS OF URINARY EXTRAVASATION AFTER HIGH-GRADE RENAL TRAUMA

INTRODUCTION AND OBJECTIVES: Contrast-enhanced CT of the abdomen/pelvis with delayed excretory phase is the preferred diagnostic test in renal trauma. Excretory phase allows for contrast accumulation into the collecting system to evaluate for urinary extravasation. Although usually performed at about 5 minutes, the optimal time between contrast injection and excretory phase has not been established. We hypothesized that there is an association between excretory phase timing and diagnosis of urinary extravasation. METHOD(S): From 2014-2017, imaging data on high-grade renal trauma (AAST grades III-V) were gathered from 13 Level-1 trauma centers participating as the AAST Genito-Urinary Trauma Study Group. Patients with missing initial CT scans or those who underwent immediate surgery without imaging were excluded. Initial and follow up CT scans were reviewed by 2 radiologists to evaluate for urinary extravasation. The time between the early (portal venous) and excretory phases was recorded. Follow up images were reviewed to determine if there were cases of missed urinary extravasation diagnosis. Logistic regression was used to measure the association of excretory phase timing with diagnosis of urinary extravasation. RESULT(S): From 313 patients with available initial CT, 232 (74%) had excretory phase imaging for review either at the initial contrast CT (199) or at their follow up (33). Median time between portal venous and excretory phases was 4 m (IQR: 4-7 m). Overall, 66 patients (21%) were diagnosed with urinary extravasation either at the initial (51) or at follow up CT scan (15). Of the 15 urinary extravasations diagnosed at follow up, 6 did not have excretory phase imaging initially and 9 were missed despite initial excretory phase imaging. Median time to excretory phase imaging was longer in those initially diagnosed with urinary extravasation (n=51) compared to those with missed collecting system injury (n=9) [median: 7 m, IQR: 4-10 m vs. median: 4 m, IQR: 4- 7 m, respectively; P=0.01; Wilcoxon ranked-sum test). In univariate regression, increased time to excretory phase was positively associated with finding urinary extravasation at the initial CT scan (OR: 1.2, 95% CI: 1.1-1.3). CONCLUSION(S): The timing of excretory phase imaging in the evaluation of renal trauma is important in diagnosis of urinary extravasation. Longer delays between early and excretory phase imaging is associated with increased odds of finding a collecting system injury. Although this study shows that longer time to excretory phase is preferred, we cannot yet determine what the optimal delay time is.