Gallstone ileus is one of those “don’t miss it” GI diagnoses because the vignette is usually classic—and the management is time-sensitive. If you can picture the anatomy and the radiograph in your head, you’ll catch it fast on USMLE.
The Memory Palace: “The Stone Escapes the Gallbladder, Breaks Into the Gut, and Gets Stuck at the Exit”
Imagine walking through a small museum (your GI tract). You start in the gallbladder room, pass through a broken wall into the duodenum, then walk down a long hallway until you reach the narrow exit door—where a big rock jams everything.
Rooms (aka steps of the pathophys)
- Gallbladder = “Stone Vault”
- A large gallstone sits in the gallbladder for a long time.
- Duodenum = “Broken Wall Exhibit”
- Chronic inflammation/pressure causes a cholecystoenteric fistula (most commonly cholecystoduodenal).
- Terminal ileum/ileocecal valve = “Narrow Exit Door”
- The stone travels and lodges at the ileocecal valve (narrow lumen + less peristaltic force).
One-liner:
Gallstone ileus = mechanical SBO caused by a gallstone that entered the intestine through a cholecystoenteric fistula and usually lodges at the ileocecal valve.
The Visual Mnemonic: “RIGLER = the 3 things you see”
Picture a plain abdominal film with three neon labels flashing RIGLER:
| Rigler triad finding | What it means | Why it happens |
|---|---|---|
| Pneumobilia | Air in the biliary tree | Fistula lets bowel gas into bile ducts |
| Small bowel obstruction | Dilated loops + air-fluid levels | Stone blocks small bowel |
| Ectopic gallstone | Stone in an unusual location (often RLQ) | Stone migrated into bowel lumen |
USMLE memory hook: “Air + Obstruction + Out-of-place stone” = think gallstone ileus.
High-Yield Clinical Pattern (What the stem screams)
Who gets it?
- Typically elderly patients (often women) with prior gallstone disease
- Often comorbid and may have vague symptoms until obstruction becomes clear
How it presents
- Mechanical SBO symptoms:
- Crampy abdominal pain, vomiting, distension, obstipation
- Can be intermittent/episodic (“tumbling obstruction”) as the stone moves
Best imaging test
- CT abdomen/pelvis: most sensitive
- Shows Rigler triad and can localize stone + fistula
Step-Style Differentials You Should Separate Quickly
Gallstone ileus vs acute cholecystitis
- Gallstone ileus: SBO picture + pneumobilia/ectopic stone
- Acute cholecystitis: RUQ pain, fever, + Murphy sign; HIDA nonvisualization
Gallstone ileus vs gallstone pancreatitis
- Pancreatitis: epigastric pain radiating to back, elevated lipase
- Gallstone ileus: obstruction signs, often less “pancreatitis-y” labs
Bonus classic: Bouveret syndrome (a special cousin)
- Gallstone lodges in proximal duodenum/pylorus → gastric outlet obstruction
- Think: vomiting + early satiety + epigastric fullness (not classic distal SBO)
Management (What USMLE expects you to do)
Initial
- IV fluids, electrolyte correction, NG tube if needed (standard SBO stabilization)
Definitive
- Surgery: enterolithotomy (remove stone causing obstruction)
- Often the preferred approach in older/high-risk patients
- Fistula and cholecystectomy may be addressed later or selectively depending on stability and operative risk
Test-day phrasing: Treat as mechanical SBO with operative removal of obstructing gallstone.
Quick Shareable Summary Card
- Path: Large stone → cholecystoenteric fistula → enters bowel → stuck at ileocecal valve
- Dx: CT; remember Rigler triad (pneumobilia + SBO + ectopic stone)
- Tx: Stabilize + enterolithotomy