Validation of a Renal Papillary Grading System: Comparison of Patients Forming Calcium Oxalate and Apatite Stones

Recent work has highlighted the renal papillary pathologies present in calcium stone formers. For example, evidence points to ductal plugging being especially damaging to the papillary tissue, and Randall's plaque has been correlated with stone recurrence. The objective of this study was to evaluate the reproducibility of a semiquantitative grading system that can be utilized in the operating room during endoscopic stone removal.

Clips of endoscopic video of single renal papillae, representing 3 papillae from each of 12 patients (6 majority calcium oxalate stone formers [CaOx SFs] and 6 majority apatite [CaP] SFs), were each triplicated in 3 rotations (original, 90° rotation, and vertical flip). Video clips were assessed by 4 graders who were blinded to any other data. Grades for plugging/dilated ducts, papillary pitting, loss of papillary contour, and Randall's plaque were evaluated for intra- and intergrader reproducibility.

Graders were in almost perfect agreement on ductal plugging in the papillae (kappa = 0.84), and agreement was good with Randall's plaque (kappa = 0.68), moderate for papillary pitting (kappa = 0.56), and weakest for loss of contour scores (kappa = 0.40). There was substantial agreement of sum papillary scores (kappa = 0.65). CaP SFs had higher scores for ductal plugging, pitting, and loss of papillary contour, whereas CaOx SFs had higher scores for Randall's plaque.

In this patient sample, papillary appearance differed between CaOx and CaP stone formers. Some of these differences can be reliably appreciated and quantified using the proposed papillary grading system. The grading system was reproducible across multiple graders and is designed to be used in the operating room in a manner that can be easily integrated into patient care.