Correlation between urinary tract pure stone composition and stone morphology on plain abdominal film.

BACKGROUND

Crystallographic composition of urinary tract stone varies in several chemical groups and determines the degree of fragmentation to extracorporeal shock wave lithotripsy (ESWL) which has been widely used for the treatment of renal and ureteral calculi. Visual prediction of stone composition by its morphology from plain radiograph may provide a simple method and clinical hint to decide therapeutic modalities. A prospective study was designed to determine the correlation of stone composition with its radiographic morphology.

METHODS

One hundred patients of urolithiasis with passage of stone fragments (after ESWL, surgical lithotomy or endoscopic lithotripsy) analyzed as pure stone by infrared spectrometry were reviewed by plain abdominal film to classify their morphology, location and size. Five experienced surgeons familiar with the radiographic patterns of different types of pure stones were invited to predict the stone composition on plain abdominal film.

RESULTS

Five different patterns of radiographic appearances of the stones were identified. Calcium oxalate monohydrate referred to the smooth-shaped and homogeneous ones with denser opacity. Calcium oxalate dihydrate referred to those smaller ones that had irregular margin with stippled border and were less dense. Calcium phosphate (CaP) had moderate density and size without significant figures. Struvite meant staghorn stone; usually bilateral. Uric acid referred to those being radiolucent, slightly opacified, and in large size. The 5 surgeons achieved an overall accuracy of 27.4%. There was no obvious relations between accuracy and location or size of the stones. CaP stone was the most likely to be misclassified, and achieved only 20% accuracy.

CONCLUSIONS

Different stone composition showed grossly specific radiographic appearances, but clinical test revealed poor correct rate in prediction of stone composition from plain abdominal film. The results of our study suggest that prediction of stone component based on stone morphology on plain abdominal film may not be accurate enough. Patient's clinical information and other laboratory data should be considered while interpreting plain abdominal film for better treatment choice of urolithiasis.