Coronal reconstruction of unenhanced abdominal CT for correct ureteral stone size classification

Purpose: To determine whether size measurement of a urinary calculus in coronal reconstruction of computed tomography (CT) differs from stone size measured in the axial plane, and whether the difference alters clinical decision making. Methods: We retrospectively reviewed unenhanced CT examinations of 150 patients admitted to the emergency room (ER) with acute renal colic. Maximal ureteral calculus size was measured on axial slices and coronal reconstructions. Clinical significance was defined as an upgrading or downgrading of stone size according to accepted thresholds of treatment: ≤5 mm, 6-9 mm and ≥10 mm. Results: There were 151 stones in 150 patients (male:female 115:34, mean age 41 years). Transverse stone diameters ranged from 1 to 11 mm (mean 4 mm). On coronal images, 56 (37%) stones were upgraded in severity; 46 (30%) from below 5 mm to 6 mm or more, and ten (7%) from 6-9 mm to 10 mm or more. Transverse measurement on the axial slices enabled correct categorization of 95 stones (63%). Conclusion: Transverse calculus measurement on axial slices often underestimates stone size and provides incorrect clinical classification of the true maximal stone diameter. Coronal reconstruction provides additional information in patients with renal colic that may alter treatment strategy.