Differences in Computed Tomography Density of the Renal Papillae of Stone Formers and Non-Stone-Formers: A Pilot Study

Purpose: It is thought that Randall's plaques, calcium deposits in the renal papillae of patients with nephrolithiasis, may serve as a nidus for stone formation. We examined the density of renal papillae in patients with stones and control patients using attenuation measurements (HU) on Computed Tomography (CT) to determine whether nephrolithiasis is associated with radiographic changes in renal papillae. Materials and Methods: Hounsfield density measurements of a 0.2cm(2) area of the renal papillae of 17 patients with a single renal calyceal calculus and 15 age- matched control patients were performed. Measurements were done for renal papillae upper, middle, and lower pole calyces for all patients. Statistical comparisons were made using the student's t-test. Results: Patients with nephrolithiasis and control patients were similar with respect to mean age (41.2 years versus 42.2 years, p = 0.82) and baseline serum creatinine (0.86 mg/dl versus 0.93 mg/dl, p = 0.21). Mean Hounsfield density of renal papillae of stone patients in calyces with stones was significantly greater than that of location- matched papillae from control patients (54.4 versus 36.6, p < 0.0001). Mean Hounsfield density of all papillae of the affected kidney (i. e., kidney with stone) in stone patients was significantly greater than that of control patients (50.9 versus 36.4, p < 0.0001). Mean Hounsfield density of all papillae in the stone- free kidney of stone patients was significantly greater than that of control patients (50.0 versus 36.1, p < 0.0001). In stone patients, when comparing the affected kidney with the stone- free kidney, there was no difference in mean papilla Hounsfield density (50.3 versus 50.9, p = 0.59). Conclusions: Hounsfield density of the renal papilla is significantly increased in patients with nephrolithiasis when compared with age- matched controls. This is true of calyces with stones, calyces without stones in kidneys with stones, and calyces of the contralateral stone- free kidney. There is no difference in renal papilla Hounsfield density between kidneys with and without stones in patients with nephrolithiasis. In the future, this information may be useful in predicting which patients may develop nephrolithiasis.