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Gallstones for the USMLE Step 2

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Gallstones (Cholelithiasis) for the USMLE Step 2
Overview
  • Gallstones, or cholelithiasis, are hardened deposits that form in the gallbladder. They are classified into:
    • Cholesterol stones: Most common (80%), formed due to cholesterol supersaturation in bile.
    • Pigment stones: Composed of bilirubin, more common in patients with hemolysis or biliary infections.
Pathophysiology
Cholesterol Stones
  • Result from cholesterol supersaturation, decreased bile acid secretion, or gallbladder stasis.
  • Risk factors include:
    • Obesity: Increased cholesterol synthesis.
    • Rapid weight loss: Mobilizes cholesterol from adipose stores.
    • Pregnancy and estrogen therapy: Increased cholesterol saturation in bile.
    • Metabolic syndrome: Insulin resistance leads to dyslipidemia and stone formation.
Pigment Stones
  • Form due to excess unconjugated bilirubin in bile, leading to stone formation.
  • Risk factors include:
    • Chronic hemolysis (e.g., sickle cell anemia, hereditary spherocytosis).
    • Cirrhosis and biliary infections.
Clinical Presentation
  • Asymptomatic: Most patients with gallstones remain asymptomatic.
  • Biliary colic: Symptomatic cholelithiasis, presenting with RUQ or epigastric pain lasting 30 minutes to several hours.
    • Pain may radiate to the right shoulder or back and often occurs after fatty meals.
    • Associated with nausea and vomiting but without signs of systemic inflammation.
  • Acute cholecystitis: Inflammation of the gallbladder due to cystic duct obstruction, causing:
    • Persistent RUQ pain, fever, and Murphy’s sign (pain on palpation of RUQ during inspiration).
  • Choledocholithiasis: Gallstones obstruct the common bile duct, leading to:
    • Jaundice, dark urine, and pale stools due to bile flow obstruction.
    • Elevated bilirubin and alkaline phosphatase (ALP) levels.
Biliary colic
Complications
Acute Cholecystitis
  • Caused by prolonged obstruction of the cystic duct.
    • Symptoms: RUQ pain >6 hours, fever, and leukocytosis.
    • Ultrasound findings: Gallbladder wall thickening, pericholecystic fluid, and gallstones.
    • Managed with antibiotics and cholecystectomy.
Choledocholithiasis and Cholangitis
  • Choledocholithiasis: Gallstones in the common bile duct may cause jaundice and elevated liver enzymes.
  • Cholangitis: Infection due to bile duct obstruction, presenting with Charcot’s triad: RUQ pain, jaundice, and fever.
    • Reynold’s pentad: Charcot’s triad plus hypotension and altered mental status, indicating sepsis.
    • Urgent ERCP is required for drainage and stone removal.
Gallstone Pancreatitis
  • Obstruction of the pancreatic duct by a stone, causing inflammation.
    • Symptoms: Epigastric pain radiating to the back, nausea, and vomiting.
    • Diagnosed with elevated amylase and lipase levels.
    • Treated with supportive care and, if needed, ERCP.
Diagnosis
Imaging
  • Ultrasound: The first-line imaging modality, showing echogenic stones with posterior acoustic shadowing.
  • MRCP: Magnetic resonance cholangiopancreatography used to visualize bile duct stones non-invasively.
  • ERCP: Diagnostic and therapeutic for choledocholithiasis and cholangitis.
Laboratory Tests
  • Liver function tests (LFTs): Elevated bilirubin, ALP, and GGT suggest biliary obstruction.
  • Leukocytosis: Indicative of inflammation or infection, such as acute cholecystitis or cholangitis.
Management
Asymptomatic Gallstones
  • Observation: No treatment unless the patient develops symptoms.
Symptomatic Gallstones (Biliary Colic)
  • Laparoscopic cholecystectomy: The definitive treatment for symptomatic gallstones to prevent complications.
Acute Cholecystitis
  • Antibiotics: Broad-spectrum antibiotics targeting gram-negative and anaerobic organisms (e.g., ceftriaxone and metronidazole).
  • Cholecystectomy: Performed within 72 hours of diagnosis.
Choledocholithiasis and Cholangitis
  • ERCP: Both diagnostic and therapeutic for removing stones from the common bile duct and relieving obstruction.
Key Points
  • Cholesterol stones are the most common type of gallstone, associated with obesity, rapid weight loss, and estrogen therapy.
  • Biliary colic presents as episodic RUQ pain after meals and is treated with laparoscopic cholecystectomy.
  • Complications include acute cholecystitis, choledocholithiasis, cholangitis, and gallstone pancreatitis.
  • ERCP is the treatment of choice for choledocholithiasis and cholangitis.
  • Ultrasound is the first-line imaging modality for diagnosing gallstones.

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