Renal Anatomical Factors for the Lower Calyceal Stone Formation

Abstract

Purpose: The pathogenesis of urolithiasis is mainly explained with metabolic disorders. However metabolic disorders alone are not sufficient to explain this pathology. In the present study the anatomical differences in the lower calyceal stone formers were examined on both the stone forming and contralateral normal side. The objective was to assess the effect of lower pole renal anatomy on the lower calyceal stone formation. Materials and Methods: Between July 1999 and July 2004 39 patients with non-obstructed solitary lower pole stones were studied. Mean age was 47.02 years. The anatomic factors were determined on intravenous urograms (IVU). The renal length and width and the number of major and minor calices were noted. Lower pole infundibular calyceal length (ICL) and width (IW), lower infundibular length-to-width ratio were measured. The infundibulo-ureteropelvic angle (IUPA) was measured by two methods using the angle between infundibular and ureteral axes (IUPA-1), and between infundibular and ureteropelvic axes (IUPA-2). We examined a new parameter: Renal longitudinal axis-infundibulum angle (RIA) for renal stone formation. RIA was determined between two axes, including the axis connecting the central point of the pelvis opposite the margins of inferior and superior renal sinus to midpoint of renal axis and the longitudinal renal axis (Figure 2). The data of the stone forming and non-stone forming contralateral side were compared. Statistical analysis was performed by paired-t-test. Results: The IUPA-1 of the stone forming side was more acute than the non-stone forming side, in 77% of cases. The UIPA-2 of the stone forming side was more acute than the non-stone forming side, in 72% of cases. The differences with both methods between the stone forming and contralateral normal side were statistically significant (p<0.05). Mean ICL of stone forming side was 30.20 mm whereas it was 25.51 mm in non-stone forming contralateral side. The difference between mean ICL values was statistically significant (p<0.05). The mean infundibular length-to-width ratio was 8.55±3.25 on the stone forming side and 7.09±2.90 on the non-stone forming contralateral side. The difference between two groups was statistically significant (p<0.05). The differences in RIA, infundibular width (IW), renal length, renal width and the number of major and minor calyces between stone forming and non-stone forming contralateral side were not statistically significant. Conclusion: Anatomical disorders of lower pole collecting system may be considered as factors contributing to stone formation. IUPA (1 and 2), ICL and ICL-to-IW ratio are significantly differing factors that might predispose to lower calyceal stone formation.