Residency · Residency · General Surgery
Approach to the Acute Abdomen
Overview
The acute abdomen refers to sudden onset of severe abdominal pain requiring urgent evaluation and potential surgical intervention. A systematic approach integrating history, physical examination, laboratory investigations, and imaging is essential to differentiate surgical emergencies from conditions amenable to medical management. The ability to rapidly and accurately assess the acute abdomen is one of the defining competencies of the general surgeon.
Clinical Assessment
History
A thorough history is the foundation of acute abdomen evaluation. Pain characterization should include onset (sudden versus gradual), location, radiation, quality, severity, and aggravating or relieving factors. The temporal evolution of pain provides critical diagnostic clues: colicky pain suggests obstruction, constant pain suggests peritonitis, and a crescendo pattern raises concern for ischemia. Associated symptoms including nausea, vomiting, anorexia, fever, changes in bowel habits, urinary symptoms, vaginal discharge, and last menstrual period must all be elicited. The surgical history is particularly important because prior abdominal operations predispose to adhesive disease, while prior similar episodes may suggest a recurrent process. Medical history should focus on anticoagulation, immunosuppression, cardiovascular disease (which raises the risk of mesenteric ischemia), and diabetes (which produces atypical presentations). Social history should address alcohol use (a risk factor for pancreatitis), drug use, and travel history.
Pain Localization and Differential Diagnosis
The location of abdominal pain narrows the differential diagnosis substantially. Right upper quadrant pain suggests acute cholecystitis, biliary colic, choledocholithiasis, cholangitis, hepatic abscess, hepatitis, Fitz-Hugh-Curtis syndrome, right lower lobe pneumonia, pulmonary embolism, or duodenal ulcer. Epigastric pain raises concern for acute pancreatitis, peptic ulcer disease, gastritis, myocardial infarction (particularly inferior MI), or aortic dissection. Left upper quadrant pain may indicate splenic pathology (infarct, rupture, or abscess), tail pancreatitis, left lower lobe pneumonia, or gastric ulcer.
Right lower quadrant pain most commonly represents acute appendicitis, the most common surgical emergency, but may also be caused by Meckel diverticulitis, mesenteric lymphadenitis, Crohn disease, cecal diverticulitis, ovarian torsion, ruptured ovarian cyst, ectopic pregnancy, or right ureteral calculus. Left lower quadrant pain typically points to sigmoid diverticulitis, left ureteral calculus, or ovarian pathology and ectopic pregnancy. Diffuse abdominal pain suggests bowel obstruction, mesenteric ischemia, perforated viscus, peritonitis, or non-surgical causes including diabetic ketoacidosis, sickle cell crisis, and porphyria.
Physical Examination
The examination begins with the general assessment: peritonitis patients characteristically lie still, while patients with colicky visceral pain cannot find a comfortable position and writhe. Vital signs may reveal fever, tachycardia, hypotension (suggesting sepsis or hemorrhage), or tachypnea. On inspection, the surgeon looks for distension, prior surgical scars, hernia sites, and ecchymosis -- Cullen sign (periumbilical) and Grey Turner sign (flank ecchymosis) suggest retroperitoneal hemorrhage. Auscultation may reveal high-pitched bowel sounds in early obstruction or absent bowel sounds in ileus or peritonitis. Palpation assesses for localized versus diffuse tenderness, guarding (voluntary versus involuntary), rigidity (a board-like abdomen indicating peritonitis), and rebound tenderness.
Several special signs are diagnostically useful: the Murphy sign for cholecystitis; McBurney point tenderness, the Rovsing sign, psoas sign, and obturator sign for appendicitis; and the Carnett sign for abdominal wall pathology, in which tenderness that increases with tensing of the abdominal muscles suggests a wall source rather than intra-abdominal pathology. A digital rectal exam assesses for mass, tenderness, blood, and stool quality. A pelvic examination is mandatory in all reproductive-age females.
Peritoneal Irritation
Understanding the types of abdominal pain is essential. Visceral pain is poorly localized, midline, and dull or crampy, mediated by autonomic afferents from the visceral peritoneum. Foregut organs (stomach, duodenum, liver, biliary tree, pancreas, and spleen) refer pain to the epigastrium. Midgut organs (jejunum, ileum, appendix, ascending colon, and transverse colon) refer to the periumbilical region. Hindgut organs (descending colon, sigmoid, and rectum) refer to the suprapubic or hypogastric area.
Parietal (somatic) pain is sharp, well-localized, and worsened by movement or cough, mediated by somatic afferents from the parietal peritoneum and indicating irritation by inflammation, blood, pus, or bowel contents. Referred pain is perceived at a site distant from its source: diaphragmatic irritation produces shoulder pain via the C3-C5 phrenic nerve, while ureteral pain refers to the groin or testicle.
Laboratory Evaluation
The laboratory workup for the acute abdomen includes a complete blood count (looking for leukocytosis, left shift, or anemia suggesting hemorrhage), a comprehensive metabolic panel (assessing electrolytes, renal function, glucose for DKA, and liver function tests including bilirubin), and lipase (more specific than amylase for pancreatitis). A serum lactate is important, though it must be interpreted carefully -- while elevated lactate has 83 to 100% sensitivity for mesenteric ischemia, its specificity is poor. Urinalysis screens for UTI, nephrolithiasis (hematuria), and DKA (ketones). A beta-hCG is mandatory in all reproductive-age females. Coagulation studies are obtained if the patient is anticoagulated or coagulopathic, a type and crossmatch is sent if hemorrhage is suspected, and blood cultures are drawn if sepsis is a concern.
Imaging
Plain Radiographs
An erect chest X-ray can detect free air under the diaphragm, suggesting perforated viscus, with a sensitivity of approximately 70 to 80%. Abdominal X-rays have limited utility but may show air-fluid levels and dilated loops in obstruction, pneumatosis intestinalis in ischemia, calcifications (ureteral stones, appendicoliths, or chronic pancreatitis), and characteristic volvulus patterns such as the coffee bean sign in sigmoid volvulus.
Ultrasound
Ultrasound is the first-line imaging modality for biliary pathology (cholecystitis and choledocholithiasis) and gynecologic pathology (ectopic pregnancy and ovarian torsion). It is also used for the FAST exam in trauma and as the initial study for appendicitis in pediatric and pregnant patients. Its limitations include operator dependence and reduced accuracy with obesity and bowel gas.
CT Abdomen/Pelvis with IV Contrast
CT with intravenous contrast is the most valuable imaging modality for the acute abdomen, with sensitivity exceeding 95% for appendicitis, diverticulitis, and obstruction. It identifies free air, free fluid, vascular pathology, and abscess formation. CT angiography is the study of choice for suspected mesenteric ischemia or aortic pathology. Limitations include radiation exposure, contrast allergy, renal insufficiency, cost, and time.
MRI
MRI is preferred in pregnancy because it avoids ionizing radiation and is increasingly used for appendicitis evaluation in pregnant patients. Its main limitation is restricted availability for emergent use.
Decision-Making: Operative vs. Non-Operative
Indications for Urgent/Emergent Laparotomy
Several findings mandate urgent or emergent surgical intervention: diffuse peritonitis with hemodynamic instability, pneumoperitoneum indicating perforated viscus, suspected mesenteric ischemia with peritoneal signs, evisceration, a strangulated hernia that cannot be reduced, and intra-abdominal hemorrhage with hemodynamic instability. Failed non-operative management of bowel obstruction also warrants operative intervention.
Conditions Often Managed Non-Operatively
Many acute abdominal conditions can initially be managed without surgery. These include uncomplicated diverticulitis (Hinchey I and II), partial adhesive small bowel obstruction without signs of strangulation, pancreatitis in its early management phase, uncomplicated appendicitis (though this remains controversial), and solid organ injuries in hemodynamically stable trauma patients.
Serial Abdominal Examination
Serial examination remains the most important diagnostic tool in equivocal presentations. Re-examination should occur at defined intervals of every 2 to 4 hours, ideally by the same examiner. Progression of peritoneal signs warrants operative intervention.
Special Populations
Elderly Patients
Elderly patients present unique diagnostic challenges. Their blunted inflammatory response means they may lack fever, leukocytosis, or classic peritoneal signs. They have a higher incidence of mesenteric ischemia, perforated viscus, and malignancy. Atypical presentations of appendicitis and cholecystitis are common, and delayed presentation increases morbidity and mortality. The threshold for CT imaging should be low.
Immunocompromised Patients
In HIV/AIDS patients, opportunistic infections such as CMV colitis, atypical tuberculosis, and lymphoma must be considered. Post-transplant patients have a dampened immune response, and early surgical consultation is warranted. Patients on corticosteroids may have suppressed peritoneal signs and leukocytosis, masking serious pathology.
Pregnant Patients
Pregnancy alters the evaluation in several ways. Anatomic displacement of organs shifts the appendix cephalad. Physiologic leukocytosis (up to 15,000/mm3 in the third trimester) makes white blood cell count less discriminating. Ionizing radiation should be avoided when possible, with ultrasound used first and MRI used if further imaging is needed. The most common non-obstetric surgical emergencies in pregnancy are appendicitis, cholecystitis, and bowel obstruction. Fetal monitoring is required perioperatively.
Pediatric Patients
Common diagnoses vary by age: intussusception predominates in children 6 months to 3 years, appendicitis in those older than 5 years, and Meckel diverticulum and pyloric stenosis (at 2 to 8 weeks) each have their own age predilections. History may be limited, making observation and clinical examination paramount. Ultrasound is preferred to limit radiation exposure.
<image>Anatomical diagram of the abdomen divided into nine regions (right/left hypochondrium, epigastric, right/left lumbar, umbilical, right/left iliac fossa, hypogastric) with organ pathologies listed in each region showing the differential diagnosis of acute abdominal pain by location. Include color-coded overlay of foregut (epigastric), midgut (periumbilical), and hindgut (suprapubic) visceral pain referral patterns.</image>
<image>Clinical decision-making algorithm flowchart for the acute abdomen starting with initial assessment (ABCs, vital signs, history, physical exam), branching into hemodynamically unstable (immediate resuscitation and OR) vs. stable pathways, then further branching based on peritoneal signs, imaging findings, and leading to operative vs. non-operative management paths with specific conditions listed at each endpoint.</image>
<image>Compilation of key CT scan findings in common acute abdominal emergencies: perforated viscus showing free intraperitoneal air, acute appendicitis showing dilated appendix with periappendiceal fat stranding, small bowel obstruction with transition point, and mesenteric ischemia with pneumatosis intestinalis and portal venous gas. Each panel labeled with arrows indicating key diagnostic features.</image>
Clinical Pearls
The most important diagnostic tool in the acute abdomen is serial abdominal examination by the same examiner. Peritonitis patients lie still while patients with colicky visceral pain cannot find a comfortable position. A pregnancy test must always be obtained in reproductive-age females with abdominal pain before any imaging or operative intervention. Free air under the diaphragm on an upright chest X-ray is absent in up to 20 to 30% of perforated viscus cases, making CT far more sensitive. Elderly and immunosuppressed patients may present without fever, leukocytosis, or classic peritoneal signs, and clinicians should have a low threshold for CT imaging. A normal serum lactate does not reliably exclude mesenteric ischemia, especially early in the disease course. The Carnett sign helps differentiate abdominal wall pain from intra-abdominal pathology: tenderness that increases with abdominal muscle tensing suggests an abdominal wall source. Referred shoulder pain (Kehr sign) suggests diaphragmatic irritation from free blood or subdiaphragmatic abscess. An acute abdomen with pain out of proportion to physical examination findings should raise suspicion for mesenteric ischemia.
References
- Cartwright SL, Knudson MP. Evaluation of acute abdominal pain in adults. Am Fam Physician. 2008;77(7):971-978.
- Mayumi T, Yoshida M, Tazuma S, et al. Practice guidelines for primary care of acute abdomen. J Hepatobiliary Pancreat Sci. 2016;23(1):3-36.
- Gans SL, Pols MA, Stoker J, Boermeester MA. Guideline for the diagnostic pathway in patients with acute abdominal pain. Dig Surg. 2015;32(1):23-31.
- Flasar MH, Goldberg E. Acute abdominal pain. Med Clin North Am. 2006;90(3):481-503.
