Feline Pyelonephritis Study Guide

Overview and Clinical Importance

Pyelonephritis is a bacterial infection of the renal pelvis and parenchyma that represents a significant cause of acute kidney injury (AKI) and acute-on-chronic kidney disease in cats. Unlike dogs, cats have naturally concentrated urine that provides some protection against lower urinary tract infections; however, when infection ascends to the kidneys, it can cause severe and potentially irreversible renal damage. Pyelonephritis is increasingly recognized as a common complication in cats with pre-existing chronic kidney disease (CKD), diabetes mellitus, and urinary tract obstruction.

For the NAVLE, understanding the pathophysiology, clinical presentation, diagnostic approach, and treatment of feline pyelonephritis is essential. This condition appears in approximately 8% of cats presenting with acute-on-chronic kidney disease and is a differential diagnosis that must be considered in any azotemic cat, particularly older females with concurrent CKD.

Anatomy and Pathophysiology

Feline Renal Anatomy Review

The feline kidney is a bean-shaped, unipyramidal organ with a single renal papilla (renal crest) draining into the renal pelvis. Key anatomical features include the cortex (outer layer containing glomeruli and proximal tubules), medulla (inner layer containing loops of Henle and collecting ducts), and renal pelvis (funnel-shaped structure collecting urine from the medulla). The diverticula are finger-like projections extending from the renal pelvis into the medulla.