Summary
A perinephric abscess is a purulent infection located in the perinephric space between the kidney and the Gerota fascia. While it typically occurs secondary to acute pyelonephritis, it may also be caused by hematogenous spread of bacteria from elsewhere in the body (e.g., in IV drug users). Risk factors include diabetes mellitus, pregnancy, and urinary tract obstruction or abnormalities. Perinephric abscess is insidious in onset, with nonspecific symptoms that include flank or abdominal pain, fever, chills, and dysuria. Costovertebral angle tenderness is often present on examination. Abdominal CT is the preferred method to confirm the diagnosis. Abscess drainage and antibiotic therapy are the cornerstones of treatment. Complications include extension of the abscess beyond the Gerota fascia, into the retroperitoneum (paranephric abscess), and sepsis.
Etiology
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Route of infection
- Most commonly due to local spread of infection in patients with acute pyelonephritis
- Hematogenous spread of infection from elsewhere in the body
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Pathogens
- Most commonly Enterobacteriaceae (gram-negative rods)
- Gram-positive bacteria (Staphylococcus aureus) [1]
- Candida infection (especially in immunocompromised and diabetic patients) [2]
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Risk factors
- Metabolic: diabetes mellitus (30–45% of patients with a perinephric abscess are diabetic) [3]
- Infection: conditions that predispose individuals to urinary tract infection and pyelonephritis, such as pregnancy (see pyelonephritis in pregnancy)
- Obstruction: urinary tract obstruction, e.g., nephrolithiasis, or abnormality, e.g., vesicoureteral reflux
- Iatrogenic: surgery (e.g., renal transplantation)
Clinical features
Onset is often insidious and symptoms are nonspecific, but they may include:
- Constitutional symptoms (e.g., fever, chills, fatigue)
- Flank pain, abdominal pain, and/or back pain, with costovertebral angle tenderness on examination (usually unilateral)
- Dysuria as well as other symptoms of cystitis (e.g., increased urinary frequency, urgency)
- Palpable unilateral flank mass
Diagnostics
Laboratory tests
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Blood
- ↑ WBC, ↑ CRP, ↑ ESR, normocytic anemia
- Normal or abnormal renal function parameters (e.g., ↑ creatinine, ↓ GFR)
- Blood culture
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Urinalysis
- Pyuria (→ positive esterase on dipstick test), leukocyturia, WBC casts
- Bacteriuria (→ positive nitrites on dipstick test)
- Hematuria
- Urine culture
Imaging
- Ultrasound of kidneys and retroperitoneum (initial screening test): hypo/anechoic, thick-walled structure
- Abdominal CT with contrast (for definitive diagnosis)
Treatment
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Abscess drainage
- Percutaneous, retroperitoneal drainage: preferred method (less likely to lead to complications)
- Surgical drainage (especially in cases of a large abscess and/or an anatomical abnormality, such as vesicoureteral reflux or a large kidney stone)
- Antibiotic treatment: may be sufficient in smaller abscesses (< 3 cm) but is usually paired with abscess drainage to avoid complications
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Treatment of concurrent diseases and/or complications
- Percutaneous nephrostomy may be required in cases of obstructive uropathy.
- Urolithiasis should be treated in patients with renal obstruction due to urinary stones.
- Nephrectomy may be required in patients with persistent infections and extensive kidney damage.
If possible, the abscess should be drained before empiric antibiotic therapy is initiated! However, if drainage is not immediately feasible, empiric antibiotics should be started.
“Ubi pus, ibi evacua” (Latin aphorism) – Where there is pus, evacuate it.
Complications
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Paranephric abscess
- Rupture of the Gerota fascia, leading to the secondary spread of purulent infection into the retroperitoneum
- Treatment: as with perinephric abscess
- Sepsis (urosepsis)
We list the most important complications. The selection is not exhaustive.