Abdominal Wall Abscess

An abdominal wall abscess is a localised collection of pus involving the skin, subcutaneous tissues or deeper abdominal wall layers.

Community acquired superficial abscesses are commonly caused by Staphylococcus aureus, including methicillin resistant strains where prevalent.

Postoperative or deep abdominal wall abscesses may be polymicrobial, particularly following gastrointestinal surgery, stoma complications or contamination from an underlying intra abdominal source.

The key distinction is between a simple superficial abscess that requires drainage and a deep or rapidly progressive infection that may represent infected mesh, fascial involvement or necrotising soft tissue infection.

Typical findings are localised pain, swelling, erythema, warmth and fluctuance. Spontaneous purulent drainage may occur.

Cellulitis may extend beyond the collection.

Features requiring urgent reassessment for deeper infection include:

• Pain markedly greater than expected from examination
• Rapidly spreading erythema or oedema
• Skin necrosis, bullae or crepitus
• Severe systemic toxicity
• Fascial tenderness
• Haemodynamic instability
• Failure after apparently adequate drainage

A postoperative abscess near a laparotomy wound should prompt assessment for deeper wound infection, infected haematoma, mesh infection or communication with the peritoneal cavity.

Most superficial abscesses are diagnosed clinically.

• Ultrasound: useful when fluctuance is absent or the depth of the collection is uncertain; confirm a drainable fluid cavity.
• CT with IV contrast: reserve for deep abdominal wall infection, postoperative disease, suspected mesh involvement or concern for communication with an intra abdominal process.
• Culture pus when infection is recurrent, severe, postoperative, immunocompromised, unusual or when antimicrobial resistance will alter treatment. Routine culture is also reasonable at incision and drainage, although uncomplicated cases may be treated successfully without it.

Incision and drainage is definitive treatment for a drainable abdominal wall abscess. Antibiotics alone are inadequate treatment for an established accessible pus collection.

Make an adequate incision, evacuate pus and debris and break down clinically important loculations. Routine painful packing of every uncomplicated cavity is not necessary.

Antibiotics are not mandatory after adequate drainage of every small uncomplicated abscess. Add systemic antimicrobial treatment when there is significant surrounding cellulitis, systemic inflammatory response, immunosuppression, multiple lesions, failed initial treatment, extremes of age or deep infection.

For uncomplicated surrounding cellulitis where methicillin susceptible staphylococci and streptococci are most likely:

Cephalexin 500 mg orally every 6 hours, usually for approximately 5 days if clinical response is satisfactory. Adjust for renal impairment.

When methicillin resistant Staphylococcus aureus is suspected or documented:

Trimethoprim sulfamethoxazole 160 mg/800 mg, one double strength tablet orally every 12 hours.

Reduce dosing in significant renal impairment.

Trimethoprim sulfamethoxazole has less reliable streptococcal activity, so significant nonpurulent surrounding cellulitis may require additional streptococcal coverage according to local protocol.

Severe systemic illness, extensive postoperative infection or suspected deep polymicrobial infection requires admission, urgent surgical review and broader IV therapy. A reasonable initial regimen when both resistant Gram positive and abdominal polymicrobial infection are plausible is vancomycin plus piperacillin tazobactam, followed by culture directed narrowing. IDSA recommends broad coverage when severe soft tissue infection may be polymicrobial.

Do not repeatedly drain a rapidly progressive painful abdominal wall lesion while treating it as a routine abscess. Disproportionate pain, fascial involvement, bullae, necrosis, crepitus or shock requires immediate assessment for necrotising soft tissue infection and urgent operative exploration.