Obstructive nephropathy: What the surgical pathologist should know

Obstructive nephropathy (ON) represents renal changes due to urine obstruction, regardless of cause, anywhere between the ureteropelvic junction and the urethra. Obstructive nephropathy is the most frequent diagnosis in nephrectomy specimens for nonneoplastic conditions. Nephrectomy is usually indicated for advanced disease, causing irreversible loss of renal function or other complications such as intractable pain, recalcitrant hypertension, repeated infection, or bleeding. Grossly, ON is characterized by cortical thinning and dilatation of the pyelocaliceal system. Microscopically, ON represents a type of primary tubulointerstitial nephritis in which there is marked chronic tubulointerstitial injury, with disproportionately mild glomerular and vascular changes. The morphologic changes of ON are complex but characteristic, thus amenable to an accurate diagnosis. Obstructive nephropathy, however, may be complicated by other morphologically distinctive and clinically significant conditions, which should also receive diagnostic attention. These conditions include acute pyelonephritis, chronic pyelonephritis, granulomatous pyelitis, papillary necrosis, xanthogranulomatous pyelonephritis, malakoplakia, urine polyp, and renal hematoma.