Clinical Usefulness of Unenhanced Computed Tomography in Patients with Acute Pyelonephritis

Background: Unenhanced computed tomography (UCT) may be useful for evaluating acute pyelonephritis; however, no study has compared UCT with enhanced computed tomography (ECT) as a diagnostic tool. We evaluated a clinical usefulness of UCT versus ECT in acute pyelonephritis (APN). Methods: We reviewed the clinical and radiological data from 183 APN-suspected patients who underwent UCT and ECT simultaneously at emergency room (ER) over a two-year period. Demographic, clinical parameters and computed tomography (CT) parameters of 149 patients were compared. Results: The average patient age was 61.2 (+/- 10) years: 31 patients were men. Ninety-nine (66.4%) patients showed stones (18.7%), perinephric infiltration (56%), swelling (21%), and hydronephrosis (6.7%) on UCT. Seventeen patients (11.4%) had an atypical clinical course, requiring additional tests for accurate diagnosis. In 7 patients UCT and ECT results did not differ; in 10 patients, the diagnosis changed on ECT. On ECT, 112/149 (75.2%) patients had stones (16.7%), perinephric infiltrations (57%), swelling (21%), and hydronephrosis (6.7%); 62.5% showed parenchymal involvement: 34 (22.8%) patients had no abnormal ECT findings. APN CT findings are similar on stone, perinephric infiltration, swelling and hydronephrosis on both CTs. Twelve patients (8.0%) had an abnormal ECT finding, i.e., low-grade (1 and 2) parenchymal involvement. Six (4%) patients developed contrast-induced acute kidney injury within 2 days after ECT. Conclusion: We demonstrate that UCT is not inferior to ECT as an initial tool for evaluating APN for screening nephrolithiasis and hydronephrosis without the risk of contrast-induced acute kidney injury (CIAKI). However, patients with an atypical clinical course may still need ECT.