Acute Appendicitis (Adult)

1. Overview

Acute Appendicitis is the most common non-traumatic surgical emergency worldwide, characterized by the acute inflammation of the vermiform appendix. It represents the surgical "bread and butter," with a lifetime risk of ~7-9%. [1]

The clinical significance of appendicitis lies in its unpredictable progression: while many cases remain uncomplicated, delayed diagnosis leads to perforation, abscess formation, and life-threatening peritonitis. The 2024 management paradigm has been reshaped by the APPAC II and CODA trials, which established Non-Operative Management (NOM) with antibiotics as a viable alternative to surgery for uncomplicated cases without an appendicolith. [2]

However, Laparoscopic Appendicectomy remains the gold standard for definitive cure, particularly in the presence of an appendicolith or suspected complication. The diagnosis is increasingly imaging-based in adults (CT-first), while ultrasound remains the primary modality in children and pregnancy. [3]

2. Epidemiology

The Demographic Peak

• Peak Age: 10-30 years. It is relatively rare in the very young and very old, but these groups have the highest rates of perforation (up to 80% in those > 80 years) due to blunted symptoms and a smaller omental "abdominal policeman." [4]
• Sex: Slight male predominance (1.4:1).

The Role of Fiber

Epidemiological studies suggest that a low-fiber, high-sugar diet contributes to the formation of appendicoliths (faecoliths), which are the primary driver of obstruction in adults.

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3. Aetiology & Pathophysiology

⚠️ THE 7-STEP MOLECULAR MECHANISM

1. Luminal Obstruction: The inciting event is the occlusion of the narrow appendiceal lumen. In adults, this is usually an appendicolith; in children, it is lymphoid hyperplasia (post-viral).
2. Mucus Distension: Behind the blockage, mucosal goblet cells continue to secrete mucus. Intraluminal pressure rises rapidly, exceeding the venous pressure (~30 mmHg).
3. Venous Congestion & Oedema: Elevated pressure inhibits venous and lymphatic drainage. The appendiceal wall becomes oedematous and haemorrhagic.
4. Bacterial Overgrowth: Stasis allows the normally low concentration of bacteria to explode. E. coli and B. fragilis proliferate and begin to invade the weakened mucosa.
5. Ischaemic Necrosis: As pressure continues to rise, it eventually exceeds the Arterial Perfusion Pressure. The antimesenteric border (the "watershed" zone) undergoes infarction and gangrene.
6. Perforation: The gangrenous wall loses structural integrity, typically at the tip, leading to the spill of pus and faecal material into the peritoneal cavity.
7. The Omental Wrap: The greater omentum migrates to the site of inflammation. If successful, it forms a Phlegmon or walled-off abscess. If unsuccessful, it leads to Generalized Peritonitis. [5, 6, 7]

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4. Clinical Presentation

The "Pain Migration" Sequence

• Visceral Phase (T10): Dull, vague periumbilical pain (midgut distribution). Associated with the "70% anorexia" rule.
• Somatic Phase (RIF): After 12-24h, the sharp pain migrates to the Right Iliac Fossa as the parietal peritoneum becomes irritated.

Physical Signs (The "Surgical" Hand)

1. McBurney's Tenderness: Maximal 1/3 of the distance from the ASIS to the umbilicus.
2. Rovsing's Sign: Pain in the RIF when the LIF is palpated (Peritoneal stretch).
3. Psoas Sign: Pain on hip extension (Suggests Retrocaecal position - 65% of cases).
4. Obturator Sign: Pain on internal rotation (Suggests Pelvic position). [8]

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5. Investigations

Scoring Systems: The Alvarado Score

• Score less than 4: Low risk (Consider discharge).
• Score 4-6: Moderate risk (Needs CT/Imaging).
• Score > 7: High risk (Surgical consult).

Imaging: The CT Gold Standard

• CT Abdomen/Pelvis (with IV Contrast): Sensitivity > 95%. Findings: Appendix > 6mm, wall thickening, "fat stranding," and presence of an appendicolith.
• Ultrasound: First-line in children/pregnancy. Look for the "Target Sign." [9]

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6. Management: Surgery vs. Antibiotics

1. Laparoscopic Appendicectomy (The Gold Standard)

• Technique: 3-port approach. Dissection of the Mesoappendix and ligation of the Appendicular Artery (a branch of the ileocolic).
• Complications: Wound infection, pelvic abscess (higher in laparoscopy vs open), and Stump Appendicitis (if > 5mm left behind). [10]

2. Non-Operative Management (NOM)

• Evidence: The APPAC II trial showed that antibiotics alone (e.g., Amoxicillin-Clavulanate) are successful in 60-70% of uncomplicated cases.
• The Trap: 30% recurrence rate within 1 year. NOM should be avoided if an appendicolith is present (high failure/perf rate). [11]

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7. Evidence: Landmark Trials

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8. Single Best Answer (SBA) Questions

Question 1

A 25-year-old male presents with 12 hours of periumbilical pain shifting to the RIF. He is anorexic but currently hemodynamically stable. CT shows an 8mm appendix with fat stranding and a 4mm appendicolith. What is the most appropriate management?

• A) Start IV Co-amoxiclav and discharge
• B) Observation for 24 hours
• C) Laparoscopic Appendicectomy
• D) Colonoscopy to exclude malignancy
• E) Ultrasound to confirm CT findings
• Answer: C. The presence of an appendicolith on CT is a strong predictor of antibiotic failure and increased risk of perforation. Surgical removal is the standard of care in this setting.

Question 2

In the 7-step molecular mechanism of appendicitis, which event directly follows the rise in intraluminal pressure above the venous pressure?

• A) Arterial infarction
• B) Bacterial translocation and overgrowth
• C) Omental migration
• D) Referred pain to the T10 dermatome
• E) Formation of a faecolith
• Answer: B. Venous congestion leads to mucosal oedema and compromised barrier function, allowing resident bacteria to multiply and invade the wall.

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9. Viva Scenario: The "Elderly" Perforation

Examiner: "An 85-year-old presents with a slightly tender abdomen and a WBC of 11. Their CRP is 300. What is your concern?"

Candidate:

1. High Suspicion: I am extremely concerned about Perforated Appendicitis.
2. The Aging Trap: Elderly patients often have blunted physiological responses; they may lack guarding or high leucocytosis despite a catastrophic intra-abdominal event.
3. Pathology: They have a high risk of "silent" perforation because their appendicular artery is often already atherosclerotic, leading to faster ischaemic necrosis.
4. Action: I would proceed immediately to a CT scan and prepare for surgery, regardless of the soft clinical examination. [12]

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10. Patient Explanation

"Appendicitis is an infection in a small, finger-shaped pouch attached to your large bowel. It's usually caused by a small blockage that traps bacteria inside. Think of it like a blocked pipe that's beginning to leak. The best treatment is usually a 'keyhole' surgery to remove the appendix before it bursts. Most people go home the next day and are back to normal within two weeks."

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11. References

1. Bhangu A, et al. Acute appendicitis: modern understanding. Lancet. 2015. [PMID: 26460662]
2. The CODA Collaborative. A Randomized Trial Comparing Antibiotics with Appendectomy. N Engl J Med. 2020. [PMID: 33017106]
3. Di Saverio S, et al. 2020 WSES Jerusalem guidelines for diagnosis and treatment of acute appendicitis. World J Emerg Surg. 2020. [PMID: 32295644]
4. Salminen P, et al. Antibiotic Therapy vs Appendectomy for treatment of uncomplicated acute appendicitis (APPAC). JAMA. 2015. [PMID: 26080338]
5. Silen W. Cope's Early Diagnosis of the Acute Abdomen. 22nd Edition.

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Last Updated: 2026-01-05 | MedVellum Editorial Team