A retrospective evaluation of Randall's plaque theory of nephrolithiasis with CT attenuation values

We examined the computed tomography attenuation values (HU) of renal papillae in stone formers (SF) to determine whether nephrolithiasis is associated with radiographic changes in renal papillae to investigate the Randall's plaque theory.

Two observers independently and retrospectively recorded the HU of the renal medullae and cortex in 90 patients with a unilateral single calculus within kidney or ureter, and in 104 cases in control group (CG) matched for age and renal functions.

The patient ages were similar in the stone former and control groups. However, the male-female ratio was significantly greater in the SF group (68:22) than in the CG (42:62, P<0.0001). Left-right ratio in SF group was 50:40. The inter-rater agreement was kappa=0.53 (95% CI: 0.42, 0.64). Mean HU of all papillae of affected side in stone-formers (ASSF) was significantly greater than that in CG (39.6 versus 29.6, P<0.0001). When comparing affected and non-affected sides within the SF group, there was no significant difference (39.6 versus 38.4, P=0.16). The receiver operating characteristic (ROC) analysis showed area under curve=0.94 with optimal cut-off at 34 HU. At this point the specificity, sensitivity, PPV and NPV were 90%, 90%, 33% and 99%, respectively.

HU of the renal papilla is significantly increased in SF in the affected and the non-affected kidneys when compared to the CG. This finding may form one of the risk indicators to determine the future follow up and clinical management for the potential SF.