Anatomic Predictors of Formation of Lower Caliceal Calculi: Is It the Time for Three-Dimensional Computed Tomography Urography?

Objective: To evaluate the various anatomic factors, using computed tomography urography (CTU), that predispose to a lower-pole kidney stone formation on one side compared with the other. Materials and Methods: The study included 51 patients with a solitary lower- pole stone. Lower-pole infundibulopelvic angle (IPA), infundibular width (IW), infundibular length (IL), caliceal volume (CV), and number of minor calices of the affected lower calyx and normal contralateral kidney were measured based on CTU. The IPA was measured according to the methods of Sampaio and Elbahnasy. A comparison was made using multivariate analysis to determine whether any of these measurements predisposed one side to form stones. Results: The mean IPA was 80.9 degrees (Sampaio), and 52.3 degrees (Elbahnasy) on the affected kidney and 87.5 degrees (P = 0.39) and 54 degrees (P = 0.36) on the normal side. The mean IW was 2.6 mm on affected side and 3.15 mm on the normal side (P = 0.03). The mean IL was 19.7 mm and 15.3 mm (P < 0.001) on the affected and normal kidneys, respectively. Mean CV was 1123 mm(3) on affected side and 286 mm3 on the normal side (P < 0.001). The mean number of minor calices was comparable (n = 3) on both sides with no statistical significance. Using multivariate analysis, only caliceal volume and IW sustained their significance in the final model. Conclusions: CTU is a very useful imaging modality in the diagnosis of intrarenal anatomic variation. Larger caliceal volume and narrower IW are associated with stone formation in lower calyx.