Figure 3a. Bilateral obstructing ureteral stones in a 36-year-old man who presented with flank pain and hematuria. (a) Unenhanced helical CT scan shows bilateral enlarged kidneys with perinephric stranding. (b, c) CT scans show distal left ureteral stones (b) and a tiny obstruction in the right ureterovesical junction (arrow in c). Note the soft-tissue rim sign (arrow in b).