🩺 The Acute Abdomen
Initial Assessment · Special Populations · Investigations · NSAP — MRCS Part A & B high-yield notes
Definition
The acute abdomen is defined as abdominal pain of non-traumatic origin lasting less than 5 days. Managing it is less about achieving a precise diagnosis and more about safely identifying and ruling out life-threatening emergencies.
A careful medical history and clinical examination remain the keystone of the initial assessment. However, examiners test your understanding of its limitations.
The Diagnostic Reality
The accuracy of a purely clinical diagnosis is less than 50%, and there is substantial inter-observer variation in eliciting physical signs. However, clinicians are considerably more reliable at one crucial task: distinguishing urgent from non-urgent conditions. This is the primary clinical goal.
Key Examination Principles
| Sign / Principle | What It Tests | Exam Pearl |
|---|---|---|
| Guarding | Involuntary (true) vs voluntary muscle contraction overlying peritoneal irritation | True guarding = peritonism; absent guarding does NOT exclude serious pathology (especially in elderly, obese, or on steroids) |
| Rigidity | Board-like generalised involuntary contraction — indicates generalised peritonitis | Implies diffuse peritoneal contamination — e.g., perforated viscus. Requires urgent intervention. |
| Rebound Tenderness | Pain on sudden release of pressure — indicates peritoneal irritation | Percussion tenderness is equally sensitive and less unpleasant for the patient — use it instead |
| Rovsing’s Sign | Pressure in LIF causes pain in RIF — suggests appendicitis | Caused by retrograde pressure pushing gas toward inflamed appendix |
| Murphy’s Sign | Inspiratory arrest on deep palpation of RUQ — indicates acute cholecystitis | Only positive if the arrest occurs specifically in RUQ, not LUQ (Boas’ sign) |
| Psoas Sign | Pain on passive hip extension — suggests retrocaecal appendicitis or retroperitoneal pathology | The inflamed appendix or psoas abscess irritates the psoas muscle |
| Obturator Sign | Pain on internal rotation of flexed hip — suggests pelvic appendicitis or pelvic pathology | Inflamed appendix in contact with obturator internus |
| Carnett’s Sign | Tenderness increases when the patient tenses their abdominal muscles (head raise test) | Differentiates abdominal wall pain (positive) from intraperitoneal pathology (negative — visceral pain is “screened” by tensed muscles) |
Giving opiates to a patient with an acute abdomen will mask signs and compromise the surgical assessment.
Early administration of opiate analgesia does not mask clinical signs and does not detrimentally affect surgical assessment. Withholding analgesia is inhumane and not evidence-based. Always give adequate pain relief.
If the diagnosis is unclear after initial assessment, the patient should be discharged or referred for immediate imaging.
Active observation — reassessment after 2–3 hours by the same surgeon — is a well-established, safe, and highly valuable diagnostic strategy. Time itself is a diagnostic tool.
The Acute Abdomen in the Context of Pain Character
Classically, the character of pain helps localise pathology. Colicky pain (waxing and waning) suggests obstruction of a hollow viscus (bowel, ureter, biliary tree). Constant severe pain suggests ischaemia, peritonitis, or solid organ pathology. Pain out of proportion to signs is the hallmark of mesenteric ischaemia — one of the most dangerous diagnoses to miss.
Causes by Anatomical Region
| Region | Key Diagnoses | Do Not Miss |
|---|---|---|
| RUQ | Acute cholecystitis, biliary colic, cholangitis, hepatitis | Fitz-Hugh-Curtis syndrome (perihepatic adhesions from PID) |
| Epigastrium | Peptic ulcer disease, acute pancreatitis, GORD, gastritis | AAA (referred epigastric), MI (inferior STEMI) |
| LUQ | Splenic pathology, gastric volvulus, pancreatitis (tail) | Splenic infarction/rupture, subphrenic abscess |
| RIF | Acute appendicitis, Crohn’s disease, mesenteric adenitis | Ectopic pregnancy, ovarian torsion, Meckel’s diverticulitis |
| LIF | Diverticulitis, constipation, sigmoid volvulus | Ischaemic colitis, colon carcinoma, ovarian pathology |
| Suprapubic / Pelvic | UTI, cystitis, pelvic inflammatory disease | Ectopic pregnancy, ovarian cyst torsion/rupture, cauda equina |
| Diffuse / Generalised | Peritonitis, intestinal obstruction, IBD | Mesenteric ischaemia, aortic dissection, diabetic ketoacidosis |