Abdominal Pain

Abdominal pain is one of the most common presenting complaints in medicine. Its evaluation requires a systematic approach because severity does not reliably predict the underlying condition — mild pain may herald a surgical emergency, while severe pain may be self-limited (Harrison's, p. 556).

Common Causes by Location

Region	Differential Diagnoses
Right Upper Quadrant	Cholecystitis, cholelithiasis, hepatitis, hepatic abscess, peptic ulcer, right lower lobe pneumonia
Left Upper Quadrant	Splenic pathology, gastritis, pancreatitis, left lower lobe pneumonia
Epigastric	PUD, GERD, pancreatitis, MI (referred), aortic aneurysm
Right Lower Quadrant	Appendicitis, ovarian cyst/torsion (females), ectopic pregnancy, Crohn's disease, inguinal hernia, mesenteric lymphadenitis
Left Lower Quadrant	Diverticulitis, sigmoid volvulus, ovarian pathology, ectopic pregnancy, constipation
Periumbilical	Early appendicitis, small bowel obstruction, mesenteric ischemia, gastroenteritis
Diffuse	Peritonitis, bowel obstruction, mesenteric ischemia, IBD, IBS, diabetic ketoacidosis

Most Common Diagnoses on Presentation (Harrison's, p. 556)

Nonspecific abdominal pain (most common overall)
Acute appendicitis
Urologic origin (renal colic, UTI, pyelonephritis)
Intestinal obstruction

Key History Features

Onset: Sudden (perforation, volvulus, ischemia) vs. gradual (appendicitis, cholecystitis)
Character: Colicky (obstruction, renal/biliary colic) vs. constant (peritonitis, ischemia)
Location & radiation: Right scapula (cholecystitis), back (pancreatitis, AAA), groin (renal colic)
Severity: Does not reliably correlate with disease severity
Associated symptoms: Fever, nausea/vomiting, diarrhea, hematochezia, melena, dysuria
Aggravating/relieving factors: Eating (mesenteric ischemia, PUD), movement (peritonitis)
Gynecologic history: LMP, sexual activity (ectopic pregnancy)

Physical Examination

Finding	Suggests
Guarding / rigidity	Peritonitis
Rebound tenderness	Peritoneal irritation
Murphy's sign	Acute cholecystitis
McBurney's point tenderness	Appendicitis
Rovsing's sign	Appendicitis
Psoas / obturator sign	Retrocecal appendicitis, pelvic abscess
Pulsatile abdominal mass	AAA
Absent bowel sounds	Ileus or late obstruction
High-pitched bowel sounds	Early obstruction

Diagnostic Workup

Labs

CBC: Leukocytosis (infection/inflammation), anemia (GI bleed)
BMP/CMP: Electrolytes, renal function, LFTs
Lipase/amylase: Pancreatitis
Urinalysis + urine culture: UTI, nephrolithiasis
β-hCG: All women of childbearing age (rule out ectopic pregnancy)
Lactate: If mesenteric ischemia or sepsis suspected

Imaging

Ultrasound: First-line for RUQ pathology (gallstones, cholecystitis), ovarian/testicular pathology; also preferred screening for mesenteric arterial occlusive disease (CMI Guidelines, p. 5)
CT abdomen/pelvis with contrast: Workhorse for acute abdominal pain — appendicitis, diverticulitis, obstruction, pancreatitis, malignancy; also definitive imaging for mesenteric artery stenosis (CTA preferred)
Plain X-ray: Limited use; helpful for free air (perforation), obstruction (dilated loops, air-fluid levels), or foreign bodies
MRI: Preferred in pregnancy; also for hepatobiliary workup

Red Flags Requiring Urgent Evaluation

Sudden-onset severe ("thunderclap") pain
Pain out of proportion to examination (suggests mesenteric ischemia)
Peritoneal signs (rigidity, guarding, rebound)
Hemodynamic instability
Pulsatile abdominal mass
Fever with acute abdomen
Positive pregnancy test with pelvic pain (rule out ectopic)
Signs of GI bleeding (melena, hematochezia, hematemesis)

Management Principles

Scenario	Action
Hemodynamically unstable	IV access, fluids, labs, urgent surgical consult
Peritonitis / perforation	NPO, IV antibiotics, surgical emergency
Acute appendicitis	Surgical or non-operative management per institution protocol
Biliary colic / cholecystitis	Analgesia, antibiotics (if cholecystitis), surgical referral
Renal colic	Analgesia (NSAIDs/opioids), hydration, urologic follow-up
Bowel obstruction	NPO, NGT decompression, surgical evaluation
Pancreatitis	IV fluids, analgesia, NPO, treat underlying cause
Mesenteric ischemia	Emergent CTA, vascular surgery consult, anticoagulation
Non-specific pain / IBS	Symptomatic treatment, outpatient workup

Clinical Pearl: The absence of hunger is not a reliable indicator of serious intraabdominal disease, and pain severity alone should never guide triage decisions. Every patient with acute-onset abdominal pain deserves a thorough, early evaluation (Harrison's, p. 556).

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