Imaging findings of xanthogranulomatous pyelonephritis

To define the imaging patterns of xanthogranulomatous pyelonephritis (XGP). The demographic, clinical, and imaging findings of 21 cases of pathologically proven XGP in 20 patients (bilateral in one) were evaluated. The findings of ultrasonography and CT were retrospectively evaluated with regard to distribution and extent of the disease, kidney size, the presence of calculi, hydronephrosis, and renal function. The findings were assessed by two radiologists, who established a consensus. Imaging and pathologic findings were compared. Sixteen of the 20 patients were female, and 19 were adults. Their age ranged from 3 to 16 (mean, 45) years. In all patients except one, the disease was unilateral (right: left =3D 13 :16). In one patient, XGP was bilateral, and there were thus 21 cases. Seventeen (81%) of these were diffuse, and four (19%) were focal; extrarenal extension occurred in 13 cases (62%), among which ipsilateral pleural effusion was noted in two. The kidney was enlarged diffusely in 12 cases (57%), and focally in three (14%); urinary calculi were present in 16 cases (76%), with staghorn calculi in four of these; and hydronephrosis occurred in 17 (81%). Impairment of ipsilateral renal function was noted in 13 cases (62%). Clinical findings of inflammation such as fever, pyuria, bacteriuria, or leucocytosis were noted in all patients. In addition to nephromegaly, renal function impairment, and urinary obstruction due to calculi, which are typical features of XGP, the condition may also show variable imaging findings. If the images obtained in the case of a middle-aged woman with clinical findings of urinary infection are atypical, we believe that XGP should be included in the differential diagnosis. (author)