Non-contrast CT attenuation value of renal papilla is a novel predictor of recurrence in kidney stone disease

In calcium stone formers, most stones grow attached to Randall's plaque, which can be identified by measuring the computed tomography (CT) attenuation value of renal papilla. We hypothesized that the CT attenuation value of renal papilla can predict the severity (recurrent or multiple stone former) and recurrence of the stone disease. We retrospectively reviewed the charts of 180 calcium oxalate stone formers who underwent non-contrast CT and 24-hour urine chemistry in our hospital between September 2012 and November 2021. Two observers independently measured the Hounsfield unit (HU) of the renal papilla and classified the patients into the low-HU and the high-HU value groups according to the median value (38.9 HU). The proportion of recurrent and multiple stone formers were similar between the low-HU group and the high-HU group (70.0% vs. 65.6%, 71.1% vs. 74.2%, respectively). There were also no significant differences in urinary volume, urinary excretions of each constituent, or AP(CaOx) index between the two groups. On the other hand, the recurrence rate in the high-HU value group (0.10 events/person/year) was significantly higher than that in the low-HU value group (0 events/person/year, p = 0.03). Multivariate analysis revealed that high-HU value was an independent predictor of stone recurrence (OR 1.90, 95% CI 1.00-3.64, p = 0.04) as well as medical prophylaxis. The results of this study suggest that HU value of renal papilla is a useful predictor of recurrence of stone disease.