Abdominal Pain

Abdominal pain is one of the most common presenting complaints in emergency departments and primary care, accounting for more than 8 million emergency visits annually in the United States. It spans a spectrum from benign functional disorders to immediately life-threatening surgical emergencies. Accurate localization, pattern recognition, and systematic clinical assessment are essential to distinguish conditions that require urgent intervention from those that can be managed conservatively.

Anatomy: RUQ / LUQ / RLQ / LLQ / Periumbilical / Diffuse

Localizing abdominal pain to a quadrant or region is the first and most critical step in narrowing the differential diagnosis. Each quadrant contains specific anatomical structures whose pathology produces characteristic pain patterns. Understanding referred pain (diaphragmatic irritation → shoulder pain; pelvic pathology → inner thigh) further expands the diagnostic framework.

Right Upper Quadrant (RUQ)

Left Upper Quadrant (LUQ)

Right Lower Quadrant (RLQ)

Left Lower Quadrant (LLQ)

Periumbilical

Diffuse Abdominal Pain

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Life-Threatening Causes — Don't Miss

A subset of abdominal pain presentations represent immediate surgical or vascular emergencies where delay in diagnosis directly increases mortality. These diagnoses must be considered in every patient with acute abdominal pain and explicitly ruled in or out before discharge.

Ruptured Abdominal Aortic Aneurysm (AAA)

The classic triad is sudden severe abdominal or back pain + hypotension + pulsatile abdominal mass. Ruptured AAA carries an overall mortality of approximately 85%, and even with immediate surgical intervention, operative mortality approaches 50%. Risk factors include elderly male sex, smoking history, hypertension, and known aneurysm. Hemodynamically unstable patients should go directly to the operating room without CT delay. Stable patients may undergo CTA for anatomic planning. Bedside ultrasound can rapidly confirm AAA presence (sensitivity >95% for aneurysm diameter) but cannot reliably detect retroperitoneal rupture.

Mesenteric Ischemia

The hallmark is pain out of proportion to physical examination — the patient appears to be in agony but the abdomen may be soft and non-tender on palpation initially. Acute mesenteric ischemia most commonly results from embolic occlusion of the superior mesenteric artery (SMA), often in patients with atrial fibrillation. Chronic mesenteric ischemia (intestinal angina) presents as postprandial pain and weight loss from atherosclerotic disease. Laboratory findings include elevated lactate and leukocytosis. CT angiography is the diagnostic study of choice. Without prompt revascularization, bowel necrosis → peritonitis → multiorgan failure → death.

Bowel Obstruction with Strangulation

Simple mechanical obstruction presents with colicky pain, distension, vomiting, and obstipation. When strangulation occurs (vascular compromise of the bowel wall), the pain changes from colicky to constant, peritoneal signs develop, fever and leukocytosis appear, and the patient becomes hemodynamically unstable. Multiple air-fluid levels on plain X-ray and CT confirm obstruction. Strangulated bowel requires immediate surgical exploration — bowel necrosis progresses rapidly to perforation and sepsis.

Ectopic Pregnancy

Any woman of childbearing age presenting with abdominal pain and amenorrhea must be considered to have an ectopic pregnancy until proven otherwise. Serum beta-hCG combined with transvaginal ultrasound is the diagnostic standard. An adnexal mass without intrauterine pregnancy on ultrasound with a positive beta-hCG is ectopic until proven otherwise. Rupture causes hemoperitoneum, hemorrhagic shock, and death if not treated emergently. Unruptured ectopic pregnancy can be managed medically (methotrexate) or surgically (salpingostomy or salpingectomy).

Perforated Viscus

Perforation of the stomach or duodenum (from peptic ulcer disease), colon (from diverticulitis or malignancy), or appendix causes sudden onset severe diffuse abdominal pain. The abdomen becomes board-like rigid. Free air under the diaphragm on upright chest X-ray (Rigler's sign on supine films) confirms the diagnosis. CT is more sensitive than plain films. Emergency surgery is required. Delay results in fecal peritonitis, overwhelming sepsis, and death.

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Appendicitis

Acute appendicitis is the most common surgical emergency in the United States, with a lifetime risk of approximately 7%. It occurs most frequently in the second and third decades of life but can affect any age group. Prompt diagnosis prevents the 25-30% perforation rate that dramatically increases morbidity, hospital length of stay, and mortality.

Pathophysiology

Luminal obstruction of the appendix — most commonly by a fecalith, lymphoid hyperplasia (in children and young adults), or foreign body — leads to bacterial overgrowth and mucus accumulation. Elevated intraluminal pressure impairs venous drainage, causing ischemia, transmural inflammation, and ultimately perforation if untreated. The appendix perforates into the peritoneal cavity (causing diffuse peritonitis) or becomes walled off by omentum (forming a periappendiceal abscess).

Clinical Presentation

Physical Examination Signs

Alvarado Score (MANTRELS)

A validated clinical scoring system to risk-stratify appendicitis:

Score 7–10 = high risk (surgical consultation without mandatory CT); score 4–6 = intermediate risk (CT recommended); score 1–3 = low risk (observation, discharge with return precautions).

Imaging

Treatment: Surgery vs. Antibiotics

Laparoscopic appendectomy remains the gold standard treatment. However, the landmark APPAC trial (JAMA 2015) and subsequent CODA trial (NEJM 2020) demonstrated that antibiotic-first therapy is a viable option for selected patients with uncomplicated (non-perforated) appendicitis. In the APPAC trial, 73% of the antibiotic group avoided surgery at 30 days, though 29% experienced recurrence within one year. Patients and physicians can engage in shared decision-making regarding operative versus non-operative management for uncomplicated appendicitis. Complicated appendicitis (perforation, abscess, peritonitis) requires surgery.

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Gallbladder and Biliary Disease

Biliary tract disease is one of the most common causes of acute abdominal pain requiring hospital admission, responsible for more than 200,000 cholecystectomies annually in the United States. Understanding the clinical spectrum from biliary colic to cholangitis is essential for appropriate triage and management.

Biliary Colic

Biliary colic results from episodic impaction of a gallstone at the neck of the gallbladder or cystic duct, triggered by cholecystokinin release after fatty meals. The pain is typically constant (not truly colicky despite the name), builds over 15–30 minutes, reaches a plateau, and resolves over 1–6 hours as the stone falls back into the gallbladder lumen. Radiation to the right shoulder or interscapular region occurs via phrenic nerve irritation. Nausea is common; fever and leukocytosis are absent. Ultrasound is the first-line imaging study, with 95% sensitivity for gallstones.

Acute Cholecystitis

Sustained impaction of a stone in the cystic duct leads to prolonged gallbladder distension, secondary bacterial infection, and transmural inflammation. Unlike biliary colic, cholecystitis causes persistent RUQ pain (>6 hours), fever, and leukocytosis. Murphy's sign is the clinical hallmark: deep inspiration during RUQ palpation causes pain and inspiratory arrest as the inflamed gallbladder descends into the examiner's fingers. Ultrasound findings include gallbladder wall thickening (>4 mm), pericholecystic fluid, and a sonographic Murphy's sign. Treatment is IV antibiotics followed by laparoscopic cholecystectomy (within 72 hours of admission in most cases).

Choledocholithiasis

Migration of a gallstone into the common bile duct (CBD) causes biliary obstruction with RUQ pain, jaundice, elevated serum bilirubin, alkaline phosphatase (ALP), and gamma-glutamyl transferase (GGT). Aminotransferases (AST/ALT) may be transiently elevated. ERCP (endoscopic retrograde cholangiopancreatography) is both diagnostic and therapeutic for CBD stone removal.

Acute Cholangitis

Bacterial infection of an obstructed biliary tree constitutes a medical and surgical emergency. Charcot's triad — fever/rigors + jaundice + RUQ pain — is present in approximately 70% of cases. Reynolds's pentad — Charcot's triad + septic shock + altered mental status — indicates severe cholangitis with high mortality and mandates urgent biliary decompression via ERCP or percutaneous transhepatic cholangiography (PTC). Blood cultures should be drawn before antibiotics; broad-spectrum coverage including gram-negative organisms and anaerobes is standard.

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Peptic Ulcer Disease and GERD

Peptic ulcer disease (PUD) affects approximately 4.5 million Americans annually. Helicobacter pylori infection and NSAID use account for the majority of cases. Understanding the distinct pain patterns of gastric versus duodenal ulcers is a classic clinical differentiator.

Gastric Ulcer

Gastric ulcers cause epigastric or LUQ pain that characteristically worsens with eating (food stimulates acid secretion → pain; food avoidance → weight loss). H. pylori accounts for approximately 70% of gastric ulcers; NSAIDs (which suppress prostaglandin-mediated mucosal protection) account for much of the remainder. Risk factors include smoking, alcohol, and physiological stress (stress ulcers in ICU patients). Complications include:

Duodenal Ulcer

Duodenal ulcers produce pain 2–3 hours after eating (when the stomach is empty and acid contact with the duodenal mucosa is maximal) and classically awaken the patient from sleep (nocturnal pain). Pain is characteristically relieved by eating (food buffers acid). H. pylori is present in approximately 95% of duodenal ulcer patients. The pain is typically epigastric and burning in character.

Diagnosis and Treatment

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Bowel Conditions

Inflammatory bowel disease, irritable bowel syndrome, and diverticular disease together represent the most common chronic causes of abdominal pain seen in outpatient gastroenterology practice.

Inflammatory Bowel Disease (IBD)

IBD comprises two distinct entities with overlapping features:

Irritable Bowel Syndrome (IBS)

IBS is the most common gastrointestinal disorder worldwide, affecting 10–15% of the global population. It is defined by the Rome IV criteria: recurrent abdominal pain at least 1 day per week for the past 3 months, associated with two or more of: change in stool frequency, change in stool form (consistency), and association with defecation. Subtypes include IBS with predominant constipation (IBS-C), diarrhea (IBS-D), or mixed pattern (IBS-M). The brain-gut axis dysregulation, visceral hypersensitivity, and altered intestinal motility underlie pathophysiology. IBS should be diagnosed positively based on symptom criteria — not solely by exclusion — in the absence of alarm features. Treatment includes:

Diverticular Disease

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Functional and Chronic Abdominal Pain

Functional abdominal pain disorders are among the most challenging presentations in medicine. The absence of structural pathology does not mean the pain is imaginary — central sensitization, alterations in pain processing, and biopsychosocial factors produce real, disabling symptoms. Approximately 30–40% of patients presenting with chronic abdominal pain will have a functional disorder as the primary diagnosis.

Pathophysiology of Functional Pain

Central sensitization involves amplification of pain signals at the level of the spinal cord and brain. Visceral hypersensitivity causes patients to perceive normal gut activity (gas, peristalsis) as painful. Psychological comorbidities including anxiety, depression, and post-traumatic stress disorder (PTSD) are common and bidirectional — they both worsen pain and are worsened by chronic pain. Adverse childhood experiences (ACEs) and history of physical or sexual abuse are significantly associated with functional abdominal pain syndromes.

Alarm Features That Must Prompt Organic Workup

Before attributing abdominal pain to a functional cause, the following alarm features must be actively excluded:

Diagnostic Workup for Chronic Abdominal Pain

Treatment of Functional Abdominal Pain

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Diagnostic Workup in the Emergency Setting

The systematic approach to acute abdominal pain in the emergency department begins with hemodynamic assessment and ends with a disposition decision that may range from immediate surgery to reassurance and outpatient follow-up. Speed and accuracy are simultaneously required.

Initial Assessment: ABCs and Hemodynamics

Airway, Breathing, and Circulation must be addressed first. Hypotension, tachycardia, and altered mental status indicate hemodynamic instability and narrow the differential to immediately life-threatening diagnoses: ruptured AAA, septic shock from peritonitis, massive GI hemorrhage, or ruptured ectopic pregnancy. Resuscitation (large-bore IV access, fluid resuscitation, blood products if indicated) and immediate surgical consultation proceed simultaneously with diagnostic evaluation.

History

A structured history using the OPQRST framework (Onset, Provocation/Palliation, Quality, Radiation, Severity, Timing) is essential:

Physical Examination

Systematic abdominal examination follows inspection → auscultation → percussion → palpation:

Peritoneal Signs — Surgical Emergency

The combination of involuntary guarding + rigidity + rebound tenderness indicates parietal peritoneal involvement and constitutes a surgical emergency. Immediate surgical consultation is required. Do not delay for additional imaging in an unstable patient with clear peritoneal signs.

Laboratory Evaluation

Imaging

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Key Research Papers

  1. Salminen P, et al. "Antibiotic Therapy vs Appendectomy for Treatment of Uncomplicated Acute Appendicitis: The APPAC Randomized Clinical Trial." JAMA. 2015;313(23):2340–2348. PMID: 26080338. DOI: 10.1001/jama.2015.6154
  2. Peery AF, et al. "Burden and Cost of Gastrointestinal, Liver, and Pancreatic Diseases in the United States." Gastroenterology. 2019;156(1):254–272. PMID: 30315778. DOI: 10.1053/j.gastro.2018.08.063
  3. Drossman DA. "Functional Gastrointestinal Disorders: History, Pathophysiology, Clinical Features, and Rome IV." Gastroenterology. 2016;150(6):1262–1279. PMID: 27144617. DOI: 10.1053/j.gastro.2016.02.032
  4. Lacy BE, et al. "Bowel Disorders." Gastroenterology. 2016;150(6):1393–1407. PMID: 27144627. DOI: 10.1053/j.gastro.2016.02.031
  5. Birnbaum BA, Wilson SR. "Appendicitis at the Millennium." Radiology. 2000;215(2):337–348. PMID: 10796905. DOI: 10.1148/radiology.215.2.r00ap24337
  6. Kwan KY, Nager AL. "Diagnosing Pediatric Appendicitis: Usefulness of Laboratory Markers." Am J Emerg Med. 2010;28(9):1009–1015. PMID: 20825802. DOI: 10.1016/j.ajem.2009.06.004
  7. Strate LL, et al. "Diverticular Disease as a Chronic Illness: Evolving Epidemiologic and Clinical Insights." Am J Gastroenterol. 2016;111(5):654–666. PMID: 27002798. DOI: 10.1038/ajg.2016.67
  8. Lau JY, et al. "Systematic review of the epidemiology of complicated peptic ulcer disease." Aliment Pharmacol Ther. 2011;34(3):303–315. PMID: 21631573. DOI: 10.1111/j.1365-2036.2011.04682.x
  9. Harbrecht BG, Franklin GA. "Management of acute pancreatitis." Am Surg. 2010;76(12):1298–1304. PMID: 21197200
  10. Ng SC, et al. "Worldwide incidence and prevalence of inflammatory bowel disease in the 21st century." Lancet. 2017;390(10114):2769–2778. PMID: 29050646. DOI: 10.1016/S0140-6736(17)32448-0
  11. Rubano E, et al. "Systematic review: emergency visceral artery revascularization." J Trauma Acute Care Surg. 2013;75(1):102–111. PMID: 23778446. DOI: 10.1097/TA.0b013e318295f7a8
  12. Ford AC, et al. "Global prevalence of, and risk factors for, uninvestigated dyspepsia." Gut. 2020;69(7):1190–1202. PMID: 31980995. DOI: 10.1136/gutjnl-2019-319843

Search PubMed: Abdominal Pain Emergency Diagnosis | Acute Abdomen Imaging and Surgery

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Connections

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