Acute pyelonephritis

Acute pyelonephritis denotes an acute infection of the kidney and is marked by:

• Patchy suppurative inflammation

• Tubular necrosis

• Neutrophilic casts

More advanced changes include: abscesses, necrotizing papillitis (especially in diabetes and those with obstruction), pyonephrosis (pelvis filled with pus) and eventually renal scars with fibrotic deformation of the cortex, underlying calyx and pelvis.

Pyelonephritis is most commonly the result of ascending infection, the consequence of:

1. Bacterial colonization of the distal urethra (and introitus in women)

2. Multiplication of bacteria in the bladder (cystitis)

3. Vesicoureteral reflux through an incompetent vesicoureteral orifice

4. Intrarenal reflux through open papillae to renal tissue

Haematogenous seeding of kidneys occurs most often in the setting of septicaemia or infective endocarditis and is enhanced by urinary obstruction

Clinically acute pyelonephritis is associated with flank pain, fever, dysuria, pyuria and bacteriuria. Uncomplicated acute pyelonephritis follows a benign course with antibiotic therapy but may recur or progress in the presence of vesicoureteral reflux, obstruction, immunocompromise, diabetes and other conditions.

Category: Pathology Notes