Acute pyelonephritis.

Acute pyelonephritis. The cortical surface is studded with focal pale abscesses

discrete, yellowish, raised abscesses are grossly apparent on the renal surface

suppurative necrosis seen on M/E

Large masses of intratubular neutrophils frequently extend within involved nephrons into the collecting ducts, giving rise to the characteristic white cell casts found in the urine

papillary necrosis is a distinct subtype:

pyelonephritis with urinary tract obstruction
analgesic abuse

c/f: pain at the costovertebral angle and systemic evidence of infection, such as chills, fever, and malaise; indications of bladder and urethral irritation (dysuria, frequency, urgency)

Urinary findings include pyuria and bacteriuria.