Pyelonephritis

• Pyelonephritis is inflammation of the renal pelvis and parenchyma.
• Most often occurs in cows and sows.
• Main predisposing factor is urinary stasis which can occur due to pregnancy, following service in the sow, following uterine and bladder prolapse or the use of catheters in small animals.
• Usually occurs due to ascending bacterial infection from the lower urinary tract.

Gross pathology

• Kidney may be swollen with external patchy congestion.
• The medulla has streaks of inflammatory debris that extend into the cortex.
• The renal pelvis as well as the ureters are dilated and contain pus.
• In chronic cases, the kidney is shrunken, distorted and has gray patches among a diffuse, tan discolouration. The medulla has fibrous tracts that run into the capsule.

Histopathology

• Dilated tubules filled with neutrophils.
• Presences of bacteria within the tubules.
• Necrosis of the pelvic epithelium and collecting tubules.
• In chronic cases, presence of fibrosis within the medulla as well as ascending fibrous tracts into the cortex.

Examples

• Corynebacterium renale in cattle and Eubacterium suis in pigs.

Definitons

• Pyelitis - infection involving the renal pelvis alone.
• Pyonephritis - suppuration of the whole kidney.