Case 43: Acute pyelonephritis

This 43 year old man was admitted to hospital because of increasing tiredness and dyspnoea. He was found to be severely anaemic. Investigations showed this was caused by carcinoma of the caecum. Following blood transfusions his caecal tumour was resected. One week post-operatively he developed pneumonia followed by a subphrenic abscess. There was cellulitis around the site of an intravenous infusion line and a gram-negative septicaemia was diagnosed. In spite of a wide range of antibiotics his condition continued to deteriorate and he died 2 months later.
At autopsy had acute bacterial endocarditis and acute pyelonephritis.

Macroscopic pathology

Microscopic pathology

Macroscopic examination of the tissue section shows a wedge shaped piece of renal tissue including cortex and medulla. Bluish linear streaks arranged at right angles to the capsule are seen within the renal parenchyma. If these are examined under the microscope the blue appearance is seen to be due to large numbers of neutrophil polymorphs expanding the renal interstitial tissue (1), (2). Neutrophils also extend into tubular epithelium and many tubules are dilated with neutrophils within the lumen (3). The glomeruli appear relatively spared. In the medulla neutrophils are seen within the interstitium but appear more prominent within dilated collecting tubules. The appearances are those of acute pyelonephritis.

Normal renal system tissues

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In the majority of cases infection arrives at the kidney via the urinary tract. In many cases acute pyelonephritis is associated with obstructive lesions in the urinary tract but in other cases may be related to vesico-ureteric reflux in the absence of obstruction. In the renal papillae intrarenal reflux occurs and infected urine extends into the large collecting ducts. From there the infecting organisms can spread directly into the renal parenchyma. The inflammatory process may resolve with little tissue damage or progress to chronic pyelonephritis (see case 44).

Learning objectives

1. Define the features of chronic pyelonephritis
2. Compare and contrast acute with chronic pyelonephritis (Case 44)