A stone that escapes. A wall that surrenders. A valve that was never built for this. The whole chain in five steps.
The board setup: Elderly patient, vague intermittent abdominal pain for days, high-pitched bowel sounds, no fever, no icterus. X-ray shows dilated loops, air-fluid levels, and gas inside the bile ducts. The last thing on your differential just became the answer.
See the mechanism
Challenge
Read the Room
Before the breakdown, nail the discriminating clue. No peeking.
WARM-UP
A 78-year-old woman is brought to the ED after two days of crampy, intermittent abdominal pain that temporarily improves then returns. She has nausea and multiple vomiting episodes. Her abdomen is diffusely tender with high-pitched, hyperactive bowel sounds. Temperature 37.2°C, BP 122/78 mmHg. No jaundice. No RUQ tenderness. Inspiratory halt with deep RUQ palpation is absent. Plain abdominal radiograph shows dilated small bowel loops with air-fluid levels and branching linear radiolucencies overlying the liver hilum.
Which single finding on the plain film is most specific for gallstone ileus as the cause of this patient's small bowel obstruction?
Right-click to cross out · Double-click to highlight · Tools lock after answer
The discriminating clue
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Fistula Path
The Stone's Escape Route
Chicago chain: chronic inflammation thins the gallbladder wall → stone erodes into duodenum → air refluxes (pneumobilia) → stone tumbles to the ileocecal valve (narrowest point) → complete SBO. Tap through each stage.
Fistula Journey
Stage-by-stage · tap Next Stage to advance
Stage 1 of 5 · The SetupYears of chronic cholecystitis. The gallbladder and duodenum are inflamed neighbors sitting millimeters apart. Repeated episodes of inflammation create adhesions. The walls thin. The barrier between them weakens. This is not a sudden event. It is a slow surrender over months to years.
Stage 2 of 5 · The Fistula Opens
The stone presses against the thinned shared wall and erodes through. A cholecystoduodenal fistula opens. Intestinal air immediately refluxes back into the biliary tree. That is your pneumobilia on the X-ray. The biliary tree is a sealed system. Air in it means there is a hole.
Stage 3 of 5 · Into the Bowel
The stone drops through the fistula into the duodenum. The small bowel is mostly wide enough. The stone tumbles distally. It lodges temporarily, the patient gets pain. It shifts. The pain eases. It lodges again. This intermittent, waxing-and-waning pattern over several days is the classic history of gallstone ileus. Some attending teams call it a "tumbling obstruction."
Stage 4 of 5 · The Impaction
The ileocecal valve is the narrowest segment of the entire GI tract. Think of it like a toll booth at rush hour on the highway. The stone sailed fine for miles. At the booth, it jams. Complete SBO. The colon beyond is decompressed. Plain film shows a gasless colon. All the dilation is on the small bowel side. The pain transitions from intermittent to constant.
Stage 5 of 5 · The X-ray
The full radiographic picture: 1. Pneumobilia (air in biliary tree), 2. Small bowel obstruction (dilated loops, air-fluid levels), 3. Ectopic radiopaque gallstone outside the gallbladder fossa. Together: Rigler Triad. You rarely see all three on plain film, but when you do, there is only one diagnosis.
RouteGB wall → Fistula → Duodenum → ICV
PatternSBO in elderly woman, no prior surgery, pneumobilia
PearlRigler Triad pathognomonic; rarely all 3 on plain film
TrapNo Murphy's sign: GB already decompressed via fistula
Stage 1 of 5
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Comparison
SBO Causes: Side by Side
Four causes of small bowel obstruction. The clue: pneumobilia (air in bile ducts) only happens when bowel air reaches the biliary tree through a fistula. Adhesions, hernias, and volvulus do not open that door.
Gallstone Ileus
WhoElderly woman, no prior abdominal surgery
X-rayPneumobilia + SBO + ectopic stone = Rigler triad
HistoryIntermittent crampy pain (tumbling stone), known gallstones for years
ExamNo Murphy's sign (gallbladder decompressed through fistula)
X-rayCoffee-bean sign (sigmoid) or kidney-bean; massive colonic dilation
HistorySudden abdominal distension, obstipation, no flatus
ExamMassively tympanitic, distended abdomen
LevelLARGE bowel, not small bowel
The Murphy's sign trap: Most students expect Murphy's sign because the gallbladder is involved. Wrong. The gallbladder already decompressed through the fistula when the stone escaped. No pressure left in the bag → no pain on deep RUQ palpation. The stone left the building.
Board trigger: Gallstone ileus is only 1-4% of all SBOs overall but up to 25% of SBOs in patients over 65 with no prior abdominal surgery. Elderly + female + no scar + SBO pattern = hunt pneumobilia before you default to adhesions.
Decision Tree
Work the Film
Two decision nodes. Guess before you peek.
You see an abdominal X-ray from an 82-year-old woman presenting with SBO-pattern symptoms and no prior surgical history. Dilated small bowel loops confirmed. Where do you look next on the film to distinguish gallstone ileus from other causes?
You confirm branching air overlying the hepatic hilum. Pneumobilia is present. What is the next critical finding to actively seek in order to complete the Rigler triad?
Rigler Triad Confirmed
Pneumobilia + SBO + ectopic stone. CT confirms and localizes the stone precisely before the operating room. Definitive treatment: operative enterotomy with stone extraction. Fistula repair (cholecystectomy and fistula closure) may be performed in the same operation or staged, depending on the patient's stability and the surgeon's judgment.
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Memory
Locks That Stick
Tap each hook. The blur is intentional. Your brain has to reach for the answer.
Hook Bank
🔑 Why is there no Murphy's sign in gallstone ileus?
The bouncer already left through a hole in the wall. The gallbladder decompressed when the fistula opened. No remaining pressure means no pain on deep palpation. Murphy's sign requires an inflamed, pressurized gallbladder. That ship sailed. Through a crack in the duodenum.
🔑 Why is pneumobilia the discriminating clue, not the SBO?
SBO has a hundred causes. Pneumobilia has basically three in this context: gallstone ileus, prior biliary surgery, or a biliary-enteric fistula from something more exotic. In an elderly woman with no surgical history, air in the bile ducts means one thing. Air does not belong in the biliary tree. When you see it, you found the crime scene.
🔑 Why does the pain come and go for days before the final blockage?
Tumbling obstruction. The stone is large enough to jam the ileocecal valve but small enough to travel most of the small bowel. It lodges, pain peaks. It shifts slightly, pain eases. It lodges again at the next narrow spot. By the time it hits the ICV and stops completely, the history has been days of this pattern. Intermittent colicky pain that finally becomes constant = stone found its final address.
🔑 The classic board demographic
Old woman. 70s-80s. Female-to-male ratio about 3.5:1. Known gallstones for years but never had surgery. Previous RUQ pain episodes. Now showing up with SBO and no scar. The age, sex, no surgical history combination alone should put gallstone ileus near the top. High-pitched bowel sounds plus pneumobilia on film closes it.
🔑 Rigler Triad: how to lock it in
Three things your radiologist sees: (1) air where it does not belong in the liver hilum area (pneumobilia), (2) dilated small bowel with air-fluid levels (SBO), (3) a calcium-density object outside where gallstones live (ectopic stone). Think of it as: Air in the pipes. Backup in the tubes. Rock near the exit. All three = call surgery.
Clinical Images
What It Looks Like
Tap any image for full view. These are the patterns your attending recognizes in seconds.
Rigler's Triad on plain X-ray
Acute cholecystitis: the precursor
Gallstone on ultrasound: the source
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Board Practice
Five Patients Walked In
One at a time. Shuffled every round. Right-click to cross out · Double-click to highlight · Tools lock on submit.
Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last updated July 1, 2026 at 10:03 PM ET
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