Appendicular Abscess

An appendicular abscess is a localised pus collection caused by perforated appendicitis that has been partially contained by the omentum and surrounding bowel.

Unlike an appendicular mass, the defining feature is a discrete fluid collection. This creates the possibility of image guided drainage and often allows immediate major surgery to be avoided in a stable patient.

Management therefore depends on four questions:

• Is the patient physiologically stable?
• Is there generalised peritonitis?
• Is the abscess technically drainable?
• Is infection controlled with antibiotics and drainage?

Patients usually present after several days of appendiceal symptoms.

Common findings include persistent right lower quadrant pain, fever, anorexia, malaise and local tenderness. A tender mass may be palpable.

Systemic toxicity varies. Some patients remain stable despite a large abscess, while others develop sepsis with tachycardia, hypotension, oliguria or altered mentation.

Diffuse guarding, rigidity or haemodynamic deterioration suggests rupture of containment, further perforation or uncontrolled intra abdominal infection.

Contrast enhanced CT is the investigation of choice in nonpregnant adults with suspected intra abdominal abscess. IV contrast improves definition of the abscess wall and surrounding structures. (

CT should define:

• Abscess dimensions
• Location and relationship to bowel
• Presence of several locules
• Appendicolith
• Associated phlegmon
• Free gas or distant contamination
• Potential percutaneous access route
• Alternative pathology

There is no single universal abscess diameter that mandates drainage. Size is only one consideration. Drainability depends on accessibility, loculation, clinical condition and whether antibiotics alone are controlling infection.

Obtain full blood count, C reactive protein, renal function and electrolytes. Measure lactate in systemic illness or suspected hypoperfusion.

When drainage or surgery is performed, obtain intra abdominal fluid for culture. The 2024 IDSA guideline specifically supports cultures during source control for complicated intra abdominal infection because results can guide narrowing or escalation of antimicrobial therapy.

Begin analgesia, IV fluid correction and antibiotic therapy promptly.

For community acquired infection in a stable adult:

Ceftriaxone 2 g IV every 24 hours plus metronidazole 500 mg IV or orally every 12 hours. (

For healthcare associated infection, severe sepsis or substantial resistant organism risk:

Piperacillin tazobactam 4.5 g IV loading dose followed by 4.5 g IV every 8 hours by extended infusion, with renal adjustment. (

Percutaneous drainage is preferred when there is a mature, accessible collection and drainage is technically safe. Modern intra abdominal infection guidance supports the least invasive method that provides definitive source control. Percutaneous drainage achieves successful control in most appropriately selected abdominal collections and may avoid difficult acute surgery.

Drain output and clinical response matter more than merely leaving a drain in place. Persistent fever, continued purulent output, worsening inflammatory markers or failure of the cavity to collapse warrants reassessment for inadequate drainage, loculation, retained appendicolith or another source.

Surgery is indicated with:

• Generalised peritonitis
• Septic shock from uncontrolled infection
• Abscess inaccessible to drainage with continuing sepsis
• Failure of percutaneous drainage
• Progressive bowel obstruction
• Suspected bowel necrosis or free perforation
• Clinical deterioration despite appropriate therapy

Early laparoscopic appendicectomy with abscess drainage is also acceptable in experienced centres. The operative decision should account for the degree of caecal and terminal ileal inflammation, because extensive dissection may increase bowel injury and resection risk.

After effective drainage or operative source control, current Surgical Infection Society guidance recommends no more than 4 days of antimicrobial therapy in most patients with adequate source control.

If definitive source control has not been obtained but the patient is responding clinically, a 5 to 7 day course is commonly used with ongoing reassessment. Continued fever or leukocytosis beyond this period should prompt a search for uncontrolled infection rather than automatic antibiotic continuation.