Renal or perinephric abscess - Urinary tract infections

Renal or perinephric abscess

Definition

An abscess that forms in the kidney, or in the perinephric fat, as the result of ascending infection or haematogenous spread. These have become less common, due to more effective antibiotic treatment of pyelonephritis.

Aetiology

As with other urinary tract infections, the most common organisms are E. coli and Staphylococcus.

Pathophysiology

Commonly the infection ascends via the lower urinary tract to cause pyelonephritis. In most cases, there is an underlying renal abnormality such as reflux, stone(s) or a polycystic kidney that predisposes to a focal area becoming walled off to form an abscess. Haematogenous spread accounts for âˆ¼25% of cases, e.g. in infective endocarditis, or other cause of bacteraemia. Perinephric abscesses may arise due to infection spreading from the kidney into the perinephric fat, or by direct haematogenous spread.

Clinical features

Symptoms are initially as for pyelonephritis. The diagnosis of renal abscess should be suspected in those patients who are seriously unwell, who have a known underlying renal abnormality and in those who do not improve after 5 days of appropriate antibiotic treatment.

Investigations

Urine microscopy and culture. Urinalysis may be normal if the abscess does not communicate with the urinary collecting system.

FBC and differential. U&Es and creatinine. Blood culture.

Renal ultrasound scan or CT will demonstrate a thick-walled cavity, often filled with necrotic material. It may not be possible to differentiate it from a renal cell carcinoma. CT with contrast usually shows increased contrast in a ring around the abscess. USS or CT-guided aspiration and/or drainage are useful to provide a specimen for microscopy and culture, and may be useful therapeutically.

Management

Antibiotic choice is as for pyelonephritis, until culture results are known. In large abscesses (>3 cm) medical therapy alone is often insufficient, and percutaneous drainage or even partial or total nephrectomy may be required. Longer courses of antibiotics are usually required, often 1–2 months.