In vitro analysis of urinary calculi: type differentiation using computed tomography and bone densitometry.

Thirty-six urinary stones were studied by computed tomography and bone densitometry in order to find a correlation between the chemical composition of the stones and the densitometric data. In vitro, the more common cases of lithiasis can be divided into 3 main groups: uric acid, cystine and the calcium salts, e.g. calcium oxalate monohydrate, calcium oxalate dihydrate and calcium phosphate. Struvite stones fall between the second and third groups. Computed tomography and bone densitometry can differentiate between the groups, provided that the value of the "stone mineral or calcium content" is correlated with the true calculated volume of the stone (resulting in the specific stone density) instead of the projection area (resulting in the area density). This is only possible in vitro. The in vivo application of these technologies in the treatment of stones of unknown composition could provide important information, but major restrictive factors pose difficulties. Further clinical studies are necessary, especially to define the role of bone densitometry.