TOPIC 39. ACUTE SURGICAL ABDOMEN – INFLAMMATORY CAUSES. ACUTE APPENDICITIS
1. Acute surgical abdomen – definition
Acute abdomen is a sudden or rapidly progressive abdominal condition presenting with pain and/or signs of peritoneal irritation that may require urgent surgical assessment or intervention. It is a syndrome, not a final diagnosis. Early recognition of haemorrhage, perforation, ischaemia, obstruction and sepsis is essential.
2. Inflammatory causes
- Acute appendicitis.
- Acute cholecystitis and cholangitis.
- Acute pancreatitis.
- Diverticulitis.
- Perforated peptic ulcer or other gastrointestinal perforation with peritonitis.
- Pelvic inflammatory disease and tubo-ovarian abscess.
- Inflammatory bowel disease complications and intra-abdominal abscess.
3. Initial assessment of acute abdomen
- Assess haemodynamic stability and sepsis; identify shock, peritonitis or major bleeding immediately.
- Take a focused history: onset, site, migration, character, severity, radiation, progression, aggravating/relieving factors, vomiting, bowel habit, urinary symptoms, fever, menstrual/obstetric history and previous operations.
- Examine abdomen for distension, scars, hernias, tenderness, guarding, rigidity, rebound/percussion tenderness, masses and bowel sounds; examine groins and relevant extra-abdominal systems.
- Provide analgesia and antiemetics; appropriate analgesia does not prevent accurate diagnosis.
- Keep nil by mouth if surgery may be needed, establish IV access, assess fluid status and correct dehydration/electrolyte abnormalities.
- Investigations are directed by differential diagnosis: FBC, CRP, electrolytes, renal/liver tests, lipase, urinalysis, pregnancy test where relevant, lactate and imaging.
4. Acute appendicitis – definition and aetiology
Acute appendicitis is acute inflammation of the vermiform appendix, usually following luminal obstruction. It is a common cause of acute abdominal pain requiring emergency surgical assessment.
Obstruction: lymphoid hyperplasia is common, particularly in younger patients; a faecolith may obstruct the lumen. Less common causes include parasites, foreign material and neoplasms.
Non-obstructive mechanisms: some cases may occur without demonstrable obstruction; infection and mucosal inflammation may contribute.
5. Pathogenesis
- Obstruction causes continued mucus secretion and distension of the appendiceal lumen, increasing intraluminal pressure.
- Venous and lymphatic drainage become impaired, causing congestion and oedema of the appendiceal wall.
- Progressive pressure compromises arterial perfusion, producing mucosal ischaemia and bacterial invasion of the wall.
- Inflammation progresses from mucosal involvement to transmural suppurative inflammation; necrosis and gangrene may develop.
- Perforation can occur, causing localised abscess or diffuse peritonitis. The greater omentum and adjacent bowel may wall off the process, producing a mass or phlegmon.
Pathogenesis sequence: luminal obstruction → mucus accumulation/distension → raised pressure → venous congestion and ischaemia → bacterial invasion and transmural inflammation → gangrene/perforation → abscess or peritonitis.