Porosity in Microtomography and Determination of Hounsfield Units do not Predict Calculi Fragmentation in Extracorporeal Lithotripsy: Analysis of an In-vitro Study

Extracorporeal Shock Wave Lithotripsy (SWL) remains one of the most popular methods for treating urinary lithiasis. To evaluate structural and microtomographic characteristics associated with urinary calculi fragmentation in an experimental model of SWL. Samples consisting of at least two calculi fragments obtained from patients were submitted to urological procedures. All calculi were analyzed by X-ray diffraction and a morphological evaluation (weight, length, width, and volume measurements) was conducted along with microtomographic and conventional tomographic assessments in vitro. Thereafter, each sample was submitted to SWL in a ballistic gelatin model. The fragments were separated, using a granulometric sieve, into specimens larger than 4 mm and 2 mm, which were subsequently weighed. Altogether, 48 urinary calculi were analyzed and were composed of whewellite (54%), struvite (22%), apatite (11%), uric acid (7%), cystine (4%), and whitlockite (2%). The fragmentation rate was 77.5% and 69.6% for samples > 4 mm and > 2 mm in size, respectively. Factors associated with a reduction in the effectiveness of SWL were volume, dry mass, and width of the calculus. The radiodensity and porosity of the samples evaluated by microtomography were not associated with the fragmentation of calculi. The volume, dry mass, and width of urinary calculi were positively correlated with the number of fragments larger than 4 and 2 mm in size obtained post-SWL.