Morphology of Chronic Pyelonephritis

Chronic Pyelonephritis

The characteristic changes of chronic pyelonephritis are seen on gross examination.

The kidneys usually are irregularly scarred; if bilateral, the involvement is asymmetric. This contrasts with chronic glumerulonephritis, in which both kidneys are diffusely and symmetrically scarred. the hallmarks of chronic pyelonephritis are COARSE, DISCRETE, CORTICOMEDULLARY SCARS OVERLYING DILATED, BLUNTED, OR DEFORMED CALYCES, and FLATTENING OF THE PAPILLAE. The scars can vary from one to several in number and may affect one or both kidneys. Most are in the upper and lower poles, consistent with the frequency of reflux in these sites.

The microscopic changes involve predominantly tubules and interstitium. The tubules show atrophy in some areas and hypertrophy or dilation in others. Dilated tubules with flattened epithelium may be filled with colloid casts ( thyroidization ). There are varying degrees of chronic interstitial inflammation and fibrosis in the cortex and medulla. In the presence of active infection there may be neutrophils in the interstitium and pus casts in the tubules. Arcuate and interlobular vessels demonstrate odliterative intimal sclerosis in the scarred areas; and in the presence of hypertension. hyaline arteriosclerosis is seen in the entire kidney. There is often fibrosis around the calyceal epithelium as well as a marked chronic inflammatory infiltrate. Glomeruli may appear normal expect for periglomerular fibrosis, or exhibit a variety if changes, including ischemic fibrous obliteration and secondary changes related to hypertension. Individuals with chronic pyelonephritis and reflux nephropathy who develop proteinuria in adviced stages show secondary focal segmental glumerulosclerosis.