A predictive model for stone radiopacity in kidney-ureter-bladder film based on computed tomography parameters.

OBJECTIVE: To create a model for prediction of stone radiopacity based on computed tomography (CT) parameters.

METHODS: We reviewed the medical records of 513 patients referred to our department for consultation for urolithiasis between March 2011 and December 2012. CT scan and kidney-ureter-bladder (KUB) film were reviewed to identify the value of scout film in revealing radiopaque stones and to identify parameters predicting radiopacity in scout-negative stones.

RESULTS: Of 375 patients who met inclusion criteria and were finally analyzed, all 206 visible stones in scout film were KUB radiopaque. Analyzing scout-negative stones, we found that 92 stones (54.4%) were radiopaque in KUB. Multivariate analysis showed that stone size >9.7 mm, non-midureteral stone location, anterior abdominal wall fat thickness ≤23.9 mm, and Hounsfield units >772 are all independent predictors of stone radiopacity in stones that were not visible in scout film, and the aforementioned parameters were used for the creation of a Web-based calculator.

CONCLUSION: Scout film can identify radiopaque stones in KUB with high specificity, and thus, KUB can be used for following-up stones which are visible in CT scout film. For stones that are not visible in scout film, the probability of a stone to be radiopaque in KUB can be calculated trough our predictive model.