To study patients who presented to the Emergency Department with acute renal colic to determine if resolution of hydronephrosis and pain accurately predicts stone passage on follow-up CT.

This is a secondary analysis of a multicenter prospective randomized clinical trial of patients diagnosed by computed tomography (CT) scan with a symptomatic ureteral stone < 9 mm in diameter. Participants were followed after randomization to evaluate for analgesic use and to assess stone passage and hydronephrosis on a repeat CT scan obtained at 29-36 days.

Four-hundred-three patients were randomized in the original study and patients were included in this analysis if they did not have surgery for stone removal and had a CT scan and information on pain medication at follow-up (N = 220). Hydronephrosis was detected in 181 (82%) on initial CT. At follow-up CT, 43 (20%) participants had a persistent ureteral stone. Of these patients, 36 (84%) had no pain, 26 (60%) did not have hydronephrosis, and 23 (53%) had neither pain nor hydronephrosis. Resolution of hydronephrosis was associated with stone passage (RR 4.6, 95% CI 1.9, 11.0), while resolution of pain was not (RR 1.1, 95% CI 0.9, 1.4).

In patients with urinary stone disease, stone passage is associated with resolution of hydronephrosis but not resolution of pain. In patients with persistent ureteral stones, neither pain nor hydronephrosis are consistently present. These findings have important implications on follow-up imaging of patients with urinary stone disease.