What is the differential diagnosis and initial management approach for a patient presenting with right upper quadrant (RUQ) pain?

Differential Diagnosis for Right Upper Quadrant Pain

Primary Differential Diagnoses

Acute cholecystitis is the most common diagnosable cause of RUQ pain, but over one-third of patients presenting with RUQ pain have alternative diagnoses. 1, 2

Biliary and Hepatic Causes

• Acute cholecystitis - most common cause requiring urgent surgical intervention 1
• Choledocholithiasis - stones in the common bile duct causing obstruction 3
• Acute cholangitis - infection of the biliary tree presenting with Charcot's triad (fever, jaundice, RUQ pain) 4
• Biliary colic - episodic severe pain from gallstone obstruction, typically radiating to right shoulder or back 3, 5
• Hepatitis - viral, alcoholic, or drug-induced liver inflammation 5
• Hepatic abscess - pyogenic or amebic collections 2
• Periampullary diverticulum (Lemmel syndrome) - rare cause of biliary obstruction from duodenal diverticulum compressing the common bile duct 6

Pancreatic Causes

• Acute pancreatitis - inflammation requiring amylase and lipase evaluation 3, 5
• Pancreatic head mass - malignancy causing biliary obstruction 6

Renal and Adrenal Causes

• Pyelonephritis - right kidney infection 2
• Nephrolithiasis - kidney stones causing referred pain 2
• Adrenal pathology - hemorrhage or mass lesions 2

Gastrointestinal Causes

• Peptic ulcer disease - gastric or duodenal ulceration with perforation risk 2, 7
• Duodenal pathology - including diverticulitis 6
• Hepatic flexure colitis - inflammatory bowel disease 2
• Appendicitis - retrocecal appendix can present with RUQ pain 7

Vascular Causes

• Portal vein thrombosis - acute or chronic obstruction 2
• Hepatic vein thrombosis (Budd-Chiari syndrome) 2
• Mesenteric ischemia - arterial or venous compromise 7

Thoracic Causes

• Right lower lobe pneumonia - referred pain from diaphragmatic irritation 2, 7
• Pulmonary embolism - can present with upper abdominal pain 7
• Pleural effusion 2

Critical "Can't Miss" Diagnoses

• Ectopic pregnancy - must be excluded in all women of reproductive age 3, 5
• Perforated viscus - requires emergent surgical intervention 7
• Acute coronary syndrome - myocardial infarction can present with epigastric/RUQ pain 7

Initial Diagnostic Approach

History and Physical Examination

Document specific pain characteristics: onset (sudden versus gradual), duration, quality (sharp, dull, cramping), severity, radiation pattern (right shoulder suggests biliary), and timing (postprandial suggests biliary colic). 3, 5

• Elicit Murphy's sign (inspiratory arrest during RUQ palpation) - highly suggestive of acute cholecystitis 3, 5
• Assess for fever, tachycardia, or hypotension indicating infection or sepsis 3, 5
• Document associated symptoms: jaundice (cholangitis, hepatitis), nausea/vomiting (biliary disease), changes in bowel habits (GI pathology) 3, 5
• Obtain complete medication history from past 6 weeks including prescription drugs, over-the-counter medications, and herbal supplements (drug-induced hepatitis) 3, 5
• Record alcohol intake and history of liver disease, biliary disease, or prior biliary surgery 3, 5
• Examine for hepatomegaly, splenomegaly, abdominal masses, or peritoneal signs 3, 5

Laboratory Testing

• Complete blood count to assess for leukocytosis (infection/inflammation) 3, 5
• Liver function tests: ALT, AST, alkaline phosphatase, GGT, and bilirubin to evaluate hepatobiliary disease 3, 5
• Pancreatic enzymes (amylase and lipase) to exclude pancreatitis 3, 5
• Pregnancy test for all women of reproductive age before any imaging 3, 5

Imaging Algorithm

Ultrasound is the mandatory first-line imaging modality for all patients with RUQ pain, with 96% accuracy for diagnosing gallstones and ability to rapidly identify biliary pathology. 4, 3, 8

Step 1: Right Upper Quadrant Ultrasound (Initial Study)

• Identifies gallstones, gallbladder wall thickening (>3mm), pericholecystic fluid, and sonographic Murphy sign 3, 5
• Evaluates intrahepatic and extrahepatic bile duct dilatation 4
• Provides morphologic evaluation and excludes alternative diagnoses from hepatic, renal, pancreatic, and vascular systems 4, 2
• Advantages: rapid, cost-effective, no radiation exposure, dynamic examination 3, 8

Step 2: CT Abdomen with IV Contrast (If Ultrasound Equivocal)

If ultrasound is nondiagnostic and clinical suspicion persists, obtain CT abdomen with IV contrast as the next imaging study. 4, 3

• Never order CT without IV contrast - critical findings like gallbladder wall enhancement and adjacent liver parenchymal hyperemia cannot be detected without contrast 4, 3
• Superior for detecting complications of cholecystitis: perforation, gangrene, gas formation (emphysematous cholecystitis), intraluminal hemorrhage 4, 3
• Identifies adjacent liver parenchymal hyperemia - an early finding in acute cholecystitis 4
• Important limitation: CT has only 75% sensitivity for gallstones, so negative CT does not exclude cholelithiasis 4, 3

Step 3: Additional Imaging (Selected Cases)

• Cholescintigraphy (Tc-99m HIDA scan): When ultrasound and clinical findings remain equivocal for acute cholecystitis; gallbladder nonvisualization has highest sensitivity and specificity for acute cholecystitis 4, 3
• MRI/MRCP: For detailed biliary tree evaluation, complicated ductal disease, or when patient is difficult to examine with ultrasound 3, 5

Critical Pitfalls to Avoid

• Never skip ultrasound and proceed directly to CT - ultrasound provides rapid, cost-effective diagnosis without radiation exposure 3
• Do not order CT without IV contrast for suspected cholecystitis - essential findings cannot be visualized 4, 3
• Remember CT misses 25% of gallstones - negative CT does not exclude cholelithiasis 4, 3
• Always obtain pregnancy test before imaging in women of reproductive age 3, 5
• Recognize that ultrasound has limited utility in critically ill patients where gallbladder abnormalities are common without acute cholecystitis 4
• Consider non-biliary causes early - more than one-third of RUQ pain is not from gallbladder disease 1, 2