Granulomatous pyelitis associated with urinary obstruction: A comprehensive clinicopathologic study

Urinary obstruction is rarely associated with a distinct granulomatous inflammation, which involves the pyelocalyceal system and closely simulates infectious conditions including tuberculosis. Its clinicopathologic features, however, have not been adequately studied since there are only seven isolated reported cases. In a comprehensive study of 112 kidney specimens with urinary obstruction, we identified five cases of granulomatous pyelitis. The features of these cases were detailed and compared with the previously reported cases. Among the five identified subjects, three patients had history of urolithiasis and two had ureteral stenosis and all had stent placement 7 weeks to 12 years before nephrectomy for relief of the unilateral urinary obstruction. The age distribution was between 38 and 81 years. Two had end-stage renal disease or chronic renal failure. The pyelocaliceal system showed frank hydronephrosis (1 case) or partial dilatation (4 cases) and contained cheesy and gritty material in its lumen. Each case showed severe granulomatous inflammation, which was limited to the pelvic wall and closely associated with calcified debris, necrotic inflammatory cells, and material consistent with Tamm-Horsfall protein. The kidney showed chronic tubulointerstitial nephritis but without granulomas. Cultures of urine, blood, and the renal pelvic content, and special stains of tissue sections did not show fungi or mycobacteria in any case. Many of these features were also observed in previously reported cases. Granulomatous pyelitis is a rare but distinct cliniocopathologic entity characterized by severe noninfectious granulomatous inflammation limited to the renal pelvis, which is uniformely asociated with urinary obstruction and pyelocalyceal dilatation and may develop in response to accumulated calcified material in the renal pelvis. Awareness of this entity and its characteristic clinicopathologic features also helps eliminate an infectious etiology with obvious treatment and prognostic implications.