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Renal Abscess: Symptoms, Diagnosis and Treatment

Review literature: (Angel et al., 2003) (Shu et al., 2004).

Definition of a Renal Abscess

A renal abscess is a collection of pus within the kidney. The kidney infection may extend into the retroperitoneum.

Etiology of Renal Abscess

Gram-negative Bacteria:

A renal abscess is most commonly caused by gram-negative bacteria such as E. coli and Proteus. Ascending urinary tract infections (pyelonephritis), tubular obstruction, and nephrolithiasis are common risk factors for renal abscess.

Staphylococci:

Before the antibiotic era, renal abscesses were often caused by the hematogenous spread of staphylococci. Today's risk groups for the hematogenous spread of staphylococci are intravenous drug abuse, intensive care, dialysis patients, valvular heart disease, and endocarditis.

Signs and Symptoms of a Renal Abscess

• Fever and chills
• Flank pain or abdominal pain
• Weight loss, malaise
• Urosepsis

Kidney Abscess: Diagnostic Workup

Urine culture:

Urine culture can often isolate the responsible bacteria and enables antibiotic resistance testing.

Laboratory tests:

Blood culture (positive in 50%). Blood count, coagulation tests (PTT, PT), CRP, liver enzymes, creatinine. In suspected urosepsis, determine sepsis parameters such as blood gas testing, procalcitonin, AT III and fibrinogen.

Ultrasonography:

Sonographic signs for a renal abscess in renal ultrasound are a hypoechoic mass within the renal capsule, which may have inclusions of air (echogenic reflex with dorsal shadowing). Doppler sonography may show increased blood flow at the margin of the renal abscess, whereas blood flow is often not visible in the center of the mass. CT should be initiated in case of abnormalities in the sonography.

Renal ultrasound imaging of a large renal abszess due to a pelvic kidney stone (1): hypoechoic regions (2) and inclusion of air (3).

Renal ultrasonography with a small renal abscess. With kind permission, Dr. med. H. Kempter, Augsburg.

Computed tomography:

A CT scan is the diagnostic test of choice [fig. renal abscess]. The renal abscess appears as a hypodense area. Air inclusion is possible. After administration of contrast medium, the abscess capsule has a ring-like enhancement.

Septated left-sided renal abscess and perinephric abscess with air inclusions. With kind permission, Dr. G. Antes, Kempten.

Intravenous urography:

Intravenous urography has only historical value and is now replaced by CT. Urography may be normal and may fail to diagnose renal abscess. If done, KUB X-ray may show an increased renal shadow and nephrolithiasis. The excretion of contrast medium is often delayed with a displacement of the pyelocalyceal system.

Treatment of a Renal Abscess

Cornerstones in the treatment of renal abscess are parenteral antibiotics and abscess drainage:

• Parenteral antibiotics: e.g., amoxicillin and clavulanic acid 2,2 g 1–1–1 i.v. in combination with gentamicin 3 mg/kg 1–0–0 i.v. Alternatives are third-generation cephalosporins.
• Abscess drainage: renal abscess larger than 3 cm diameter should be drained. Pus is sent for identification of bacteria and antibiotic resistance testing. Renal abscess larger than 5 cm diameter may need repeated or several parallel pigtail drains.
• In advanced disease, surgical drainage or nephrectomy is rarely necessary, depending on renal function.

References

Shu u.a. 2004 SHU, T. ; GREEN, J. M. ; ORIHUELA, E.: Renal and perirenal abscesses in patients with otherwise anatomically normal urinary tracts.
In: J Urol
172 (2004), Nr. 1, S. 148–50

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