Surgeons treating one of endourology’s most stubborn problems now have a new tool to tell them, before the first incision, whether a minimally invasive approach is likely to succeed. A retrospective study of 52 patients has validated a novel radiological grading system, the L.E.N.S.O. score, which predicts how difficult it will be to clear stones lodged inside calyceal diverticula, small pouches that bud off the kidney’s collecting system. The findings, published in the African Journal of Urology, show a striking gradient of success that tracks closely with the score, from near-certain cure in the simplest cases to a one-in-four chance in the most complex ones.

Calyceal diverticula are rare congenital cystic outpouchings of the renal collecting system, with an estimated prevalence of 0.2 to 0.6 percent. They are lined with urothelium and connect to the rest of the collecting system through a narrow channel called an infundibulum. Most cause no trouble, but urine stagnates inside them and drains poorly through that narrow neck, creating ideal conditions for stone formation, chronic infection and pain. Because treatment success depends not just on the size of the stone but on the anatomy of the pouch itself, including its location, neck configuration and orientation, these cases have long frustrated urologists seeking a reliable way to plan surgery.

Historically, percutaneous nephrolithotomy, in which a tract is punched directly through the flank into the kidney, has been considered the standard treatment, delivering high stone-free rates at the cost of greater invasiveness. Advances in flexible ureteroscopes and laser lithotripsy have made the retrograde route, threading a scope up the ureter, an increasingly viable alternative for selected patients. But reported stone-free rates after ureteroscopic treatment vary widely, largely reflecting differences in how accessible each diverticulum is. Until now, no standardized classification system integrated the anatomical factors that drive those differences.

The surgeons used radial shallow cuts rather than a single deep incision, a strategy designed to prevent bleeding, and employed a 30-watt holmium laser with energy settings adjusted to the thickness of the infundibulum and the stone burden.

The L.E.N.S.O. acronym captures the five radiological parameters scored on contrast-enhanced CT imaging: Location, Excretion, Neck visibility, Stone size and Orientation. Each component receives one or two points, giving a total score between 5 and 10. Patients were stratified into low complexity, a score of 6 or less; moderate complexity, 7 to 8; and high complexity, 9 or more. To ensure they were dealing with true congenital diverticula rather than acquired conditions such as hydrocalyx or post-infectious deformities, the team applied strict radiological criteria, including delayed filling and emptying of contrast and the absence of functioning parenchyma within the diverticular wall.

The results revealed a clear dose-response relationship between anatomical complexity and outcome. Overall, the stone-free rate, defined as the absence of residual fragments larger than 3 millimeters, was 69.2 percent at three months. But that average concealed enormous variation. In the low-complexity group, 94.7 percent of patients were stone-free at three months and not one required an auxiliary procedure. In the high-complexity group, only 25 percent achieved stone-free status and 75 percent needed additional interventions, including repeat ureteroscopy, percutaneous nephrolithotomy or shock wave lithotripsy. Operative time and hospital stay also rose steadily with the score.

Multivariate logistic regression identified two independent predictors of treatment failure: poor excretion of contrast into the diverticulum, with an odds ratio of 0.24, and a neck that was not visible on preoperative imaging, with an odds ratio of 0.26. Both point to the same underlying problem, a narrow, tortuous or occluded diverticular neck that is hard to find and harder to cannulate. When the neck could not be readily identified during surgery, which occurred in roughly a third of patients, the team used methylene blue dye testing, instilling dilute dye retrograde until it escaped from the hidden ostium. Despite these challenges, the diverticular neck was successfully identified and accessed in all 52 patients, a 100 percent technical success rate.

Receiver operating characteristic analysis quantified the score’s discriminatory power, yielding an area under the curve of 0.87, which the authors interpret to mean that in 87 percent of paired comparisons, a randomly selected patient who became stone-free had a more favorable score than one who did not. The optimal cut-off of 7 or less predicted stone-free status with 86.1 percent sensitivity and 81.3 percent specificity, a positive predictive value of 91.2 percent and an overall accuracy of 84.6 percent. Stone-free rates declined significantly with each increment in score, a trend the authors report as highly statistically significant.

The clinical implications are straightforward. Patients scoring 6 or below are ideal candidates for the retrograde approach, with expected stone-free rates above 90 percent and minimal risk of secondary procedures. Those in the middle band, who made up nearly half the cohort, should be counselled that roughly two-thirds will be cleared by a single procedure and that residual fragments or secondary interventions are possible. For high-complexity patients, the authors argue that alternatives deserve serious consideration, including primary percutaneous nephrolithotomy, laparoscopic or robotic-assisted diverticulectomy, or even conservative observation if symptoms permit. Notably, a prior history of percutaneous surgery did not worsen retrograde outcomes in this cohort, suggesting such patients need not be excluded.

The authors are careful to frame the work as exploratory. The study was retrospective and single-center, the sample was small, and the score was developed and validated on the same cohort, which may overestimate its predictive accuracy; external validation in an independent, preferably multicenter cohort is planned before widespread adoption. The score also depends on contrast-enhanced imaging, which is not suitable for all patients. Still, if the findings hold, a five-point checklist read off a CT scan could spare the most complex patients an operation destined to fall short, while reassuring the rest that a scope and a laser are all they are likely to need.

Subject of Research: Validation of a radiological complexity score for predicting outcomes of flexible ureteroscopic treatment of calyceal diverticular stones

Article Title: Flexible ureteroscopic management of calyceal diverticular stones: outcomes and validation of the novel L.E.N.S.O. radiological complexity score

Article References: Ashraf, W., Iqbal, T., & Nazir, S. S. (2026). Flexible ureteroscopic management of calyceal diverticular stones: outcomes and validation of the novel L.E.N.S.O. radiological complexity score. African Journal of Urology, 32(1), Article 60. https://doi.org/10.1186/s12301-026-00607-0

Image Credits: AI Generated

DOI: 10.1186/s12301-026-00607-0

Keywords: calyceal diverticulum, kidney stones, flexible ureteroscopy, L.E.N.S.O. score, laser infundibulotomy, retrograde intrarenal surgery, radiological scoring, stone-free rate, holmium laser, endourology, predictive model, urology