US and CT findings of xanthogranulomatous pyelonephritis.

Ultrasonographic and computed tomographic findings of 21 cases of pathologically proven xanthogranulomatous pyelonephritis (XGP) in 20 patients were retrospectively evaluated. Seventeen (81%) were diffuse, and extrarenal extension occurred in 13 cases (62%). The kidney was enlarged diffusely in 12 cases (57%), and focally in 3 (14%). Urinary calculi were present in 16 cases (76%), with staghorn calculi in 4 of these, and hydronephrosis occurred in 17 (81%). In addition to typical features of XGP, the condition may also show variable imaging findings.