What is the treatment for a flank abscess?

Treatment of Flank Abscess

Flank abscesses require percutaneous or surgical drainage as the primary treatment, combined with broad-spectrum antibiotic therapy covering Gram-positive, Gram-negative, and anaerobic organisms. 1, 2

Primary Treatment: Source Control

Drainage is Mandatory

• Percutaneous drainage combined with antibiotic therapy for 4 days is the preferred approach for large abscesses in immunocompetent, non-critically ill patients. 1
• Surgical drainage should be considered when percutaneous drainage is not feasible or available, particularly in critically ill or immunocompromised patients. 1, 3
• Surgical drainage achieves shorter hospitalizations compared to percutaneous drainage (15.9 vs 28.5 days) and is superior for complex abscesses with sepsis. 4, 3
• Multiple counter-incisions rather than a single long incision should be used for large abscesses to prevent step-off deformity and delayed wound healing. 2
• Thorough evacuation of pus and probing the cavity to break up loculations is essential. 2

When Drainage is Not Immediately Available

• If percutaneous drainage is not feasible in immunocompetent, non-critically ill patients, antibiotics alone could be considered as primary treatment. 1
• However, in critically ill or immunocompromised patients without drainage availability, surgical intervention should be the primary treatment. 1

Antibiotic Therapy

Empiric Regimen Selection

For immunocompetent, non-critically ill patients with adequate source control:

• Piperacillin/tazobactam 6 g/0.75 g loading dose, then 4 g/0.5 g q6h or 16 g/2 g by continuous infusion. 1
• Alternative: Eravacycline 1 mg/kg q12h. 1

For critically ill or immunocompromised patients:

• Piperacillin/tazobactam (same dosing as above) or Eravacycline 1 mg/kg q12h. 1
• Consider broader coverage including vancomycin or daptomycin for MRSA, third-generation cephalosporin for Gram-negatives, and metronidazole for anaerobes. 5

For patients with inadequate/delayed source control or high risk of ESBL-producing Enterobacterales:

• Ertapenem 1 g q24h or Eravacycline 1 mg/kg q12h. 1

If septic shock is present:

• Meropenem 1 g q6h by extended infusion or continuous infusion, OR 1
• Doripenem 500 mg q8h by extended infusion or continuous infusion, OR 1
• Imipenem/cilastatin 500 mg q6h by extended infusion, OR 1
• Eravacycline 1 mg/kg q12h. 1

For documented beta-lactam allergy:

• Eravacycline 1 mg/kg q12h or Tigecycline 100 mg loading dose then 50 mg q12h. 1

Duration of Antibiotic Therapy

• 4 days in immunocompetent, non-critically ill patients if source control is adequate. 1
• Up to 7 days based on clinical conditions and inflammation indices in immunocompromised or critically ill patients if source control is adequate. 1
• 2-6 weeks for complex cases or inadequate drainage. 5
• Patients with ongoing signs of infection or systemic illness beyond 7 days warrant diagnostic re-investigation. 1, 5

Microbiologic Considerations

Expected Pathogens

• Primary flank/psoas abscesses: Staphylococcus aureus is most common, followed by Streptococcus agalactiae, E. coli, viridans streptococci, and Salmonella spp. 4
• Secondary abscesses (from GI/GU sources): E. coli is the leading organism, followed by S. aureus, Klebsiella pneumoniae, viridans streptococci, and Candida albicans. 4
• Antibiotic regimens should be adjusted based on culture results. 5

Special Situations

Multiloculated Abscesses with Intraosseous Extension

• Require aggressive surgical drainage with bone debridement if necessary, combined with broad-spectrum IV antibiotics. 2
• Cannot be adequately managed with antibiotics alone or simple drainage procedures. 2

Dropped Gallstones After Laparoscopic Cholecystectomy

• Flank abscesses may result from stone migration to extraperitoneal sites. 6
• Ultrasound may reveal subcutaneous tracks and stones requiring laparoscopic exploration and stone retrieval. 6

Cryptococcal Infection (Rare)

• In immunocompetent patients with disseminated cryptococcal disease presenting as flank abscess, one-week intravenous amphotericin B and flucytosine followed by oral antifungals is effective. 7

Critical Pitfalls to Avoid

• Delayed surgical intervention worsens outcomes—control sepsis but avoid prolonged delay that increases complication risk. 2
• Needle aspiration should not be attempted as it has low success rates (25% overall, <10% with MRSA). 2
• Failure to obtain cultures before initiating antibiotics limits ability to tailor therapy. 5
• Persistent fever, bacteremia, or failure to improve indicates inadequate source control requiring repeat imaging and potential reoperation. 2