Appendicular Abscess — A Detailed Overview

Definition and Pathogenesis

1. Free perforation → diffuse peritonitis (if the contamination is not contained)
2. Walled-off perforation → localized abscess (if the omentum, loops of small bowel, or retroperitoneal position seals off the leak)

"An abscess will develop after perforation if the perforated appendix is walled off from the remainder of the peritoneal cavity because of its retroperitoneal location or by loops of small intestine or omentum. A localized collection of inflammatory tissue (phlegmon) initially forms, and subsequently a true abscess develops." — Sleisenger and Fordtran's Gastrointestinal and Liver Disease

Epidemiology

• Overall perforation rate in appendicitis: 10–30% across most series
• Perforation rates are highest at the extremes of age:
  • Children <2 years: up to 90%
  • Patients >70 years: 50–70%
  • Ages 10–30: lowest, around 10–20%
• Risk of perforation increases significantly after 24 hours of symptoms
• Patients with perforation typically have symptoms averaging 30 hours longer than those with simple appendicitis

Clinical Features

Symptoms

• Right lower quadrant (RLQ) pain — often more prolonged than typical appendicitis (>24–48 hours)
• High-grade fever, rigors
• Nausea, vomiting, anorexia
• Diarrhea or constipation

Signs

• Significant fever and leukocytosis (more pronounced than uncomplicated appendicitis)
• Palpable RLQ mass — the hallmark; formed by the walled-off phlegmon/abscess
• Signs of local peritonism (guarding, tenderness) over the RLQ
• Rarely, if the abscess is pelvic: rectal tenderness, urinary frequency, diarrhea

"On physical examination, patients with an abscess resulting from appendicitis often have a palpable RLQ abdominal mass." — Sleisenger and Fordtran's

Imaging

CT Scan (Investigation of Choice)

• Most sensitive and specific modality
• Findings:
  • Thickened, non-filling appendix ± appendicolith
  • Periappendiceal fluid collection with enhancing wall = abscess
  • Surrounding fat stranding
  • Extraluminal gas (perforation)
  • Free intraperitoneal air (if free perforation has occurred)
• Detects abscess, phlegmon, appendicolith, free fluid, free air — all features associated with complicated appendicitis
• Guides percutaneous drainage planning

Ultrasound

• Useful in children and pregnant women; identifies fluid collection and inflamed appendix
• Operator-dependent; lower sensitivity for retroperitoneal/pelvic collections

MRI

• Reserved for pregnant patients (no radiation); performed without contrast
• Sensitivity 97%, specificity 95% for appendicitis
• Can identify abscess formation

Distinction: Abscess vs. Phlegmon

Management

FIGURE: Suggested algorithm for managing acute appendicitis with abscess or phlegmon. — Sabiston Textbook of Surgery

1. Resuscitation (All Patients)

• IV fluids, correction of electrolyte imbalances
• Broad-spectrum IV antibiotics (covering gram-negatives and anaerobes)

2. True Abscess — Image-Guided Percutaneous Drainage

• Preferred first-line approach for a drainable abscess
• CT-guided drainage is most successful; transgluteal drainage and lower-grade abscesses have better resolution rates
• Drain left in place until output ceases/slows to institutional standard
• Antibiotics continued for 4 days after source control
• Success rate: ~79% of patients achieve complete resolution
• If CT-guided drainage is not technically feasible: consider laparoscopic, transrectal, or transvaginal drainage

3. Phlegmon (No Drainable Collection)

• IV antibiotics alone for 4–7 days (per IDSA guidelines for intra-abdominal infection)
• If no improvement → re-imaging in 3–5 days to check for interval development of a drainable abscess

4. Immediate Surgery — Indications

• Diffuse peritonitis (free perforation)
• Septic/toxic patient not responding to conservative measures
• Failure of conservative management

"Immediate surgery is necessary in patients that appear septic, but this is usually associated with higher complications, including abscesses and enterocutaneous fistulae due to dense adhesions and inflammation." — Schwartz's Principles of Surgery

5. Operative Management (When Required)

• Laparoscopic appendectomy by experienced surgeons — supported by WSES Jerusalem Guidelines
• In severe inflammation: may require ileocecectomy (due to extreme induration/friability)
• Risks of immediate surgery in established abscess: failure to identify appendix, postoperative abscess, fistula, extension of resection

Antibiotic Regimens

• Piperacillin/tazobactam (monotherapy)
• Cefepime or carbapenem + metronidazole
• β-lactam allergy: clindamycin + fluoroquinolone/gentamicin/aztreonam

Interval Appendectomy

• Recurrence rate of appendicitis after nonoperative management: 8–31.8%
• Risk of finding appendiceal neoplasm: benign 0.7%, malignant 1.3%
• Appendicolith on CT predicts higher recurrence → selective indication for interval appendectomy

• 91% of patients have no further events at median 34-month follow-up
• Interval appendectomy is technically challenging (adhesions, inflammation) → higher complication rate
• WSES Jerusalem Guidelines: do NOT recommend routine interval appendectomy

"If no interval appendectomy is performed, colonoscopy and full-dose contrast-enhanced CT should be performed in all adult patients 40 and older as routine follow-up after nonoperative management of complicated appendicitis." — Sabiston Textbook of Surgery (citing WSES guidelines)

Complications of Appendicular Abscess / Perforated Appendicitis

Summary