Measurement of ureteric stones by CT in the axial plane underestimates maximal stone diameter compared with measurement in the coronal reconstruction plane, according to a study of 331 patients with ureteric colic who had unenhanced multidetector CT scans. Overall, underestimation was 20% compared with axial plane measurement, whereas for stones that passed spontaneously or with medical expulsive therapy, a 17% underestimation was seen.