Gallbladder stones exit through the common bile duct and enter the small intestine, typically the duodenum, after the gallbladder contracts to release bile. They are not expelled through the anus or urinary tract.
These stones form when substances in bile-primarily cholesterol or bilirubin-crystallize. Most pass uneventfully, but some cause obstruction. The common bile duct connects the gallbladder to the duodenum, serving as the exit route. Stones may move slowly, sometimes taking days to traverse the 7-10 cm duct.
When a stone blocks the duct, it triggers biliary colic-a sharp pain in the upper right abdomen. If the blockage persists, it can lead to cholangitis (bile duct infection) or pancreatitis. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) reports that about 10-15% of people with gallstones develop symptoms requiring medical intervention.
After forming in the gallbladder, stones remain there until the organ contracts during digestion. This contraction forces bile-and any stones-into the cystic duct, then into the common bile duct. The duct narrows to about 6 mm in diameter, which can trap larger stones.
Peristaltic contractions of the bile duct walls push the stone downward. The sphincter of Oddi, a muscular valve at the junction of the bile duct and duodenum, relaxes to allow passage. If the stone is too large (typically >8 mm), it may fail to pass and cause obstruction.
A 2021 study in *The American Journal of Gastroenterology* found that 75% of gallstones smaller than 5 mm pass spontaneously without surgery. Stones between 5-8 mm have a 40% spontaneous passage rate. Larger stones often require endoscopic removal.
Gallstones fall into two main categories: cholesterol stones and pigment stones. Cholesterol stones make up 80% of cases and form when bile contains excess cholesterol. Pigment stones-dark, granular deposits-develop from excess bilirubin, often in people with hemolytic anemia or cirrhosis.
| Type | Composition | Prevalence | Common Risk Factors |
|---|---|---|---|
| Cholesterol | Cholesterol crystals | 80% | Obesity, rapid weight loss, female gender, age >40 |
| Pigment (black) | Bilirubin, calcium salts | 10-15% | Hemolysis, liver disease, infections |
| Pigment (brown) | Bilirubin, bacterial enzymes | 5-10% | Biliary tract infections, strictures |
Cholesterol stones are usually yellowish-white and smooth. Pigment stones are darker and irregular. Brown pigment stones often form in infected bile ducts due to bacterial enzymes breaking down bilirubin into insoluble compounds.
People often assume stones exit through the rectum or urine. This is incorrect. The gastrointestinal tract is the sole exit path. Stones do not appear in stool unless they pass completely through the intestines and are excreted in feces-rarely seen and not typical.
Another misconception is that all gallstones cause pain. Many are asymptomatic. The American College of Gastroenterology notes that up to 80% of gallstones are silent and discovered incidentally during imaging for unrelated issues.
Some believe stones can dissolve on their own. While certain medications like ursodeoxycholic acid can shrink small cholesterol stones, they take months to years and work in less than half of patients. Spontaneous dissolution is rare.
In 2022, a 52-year-old woman presented with severe right upper quadrant pain lasting six hours. Ultrasound revealed a 7 mm cholesterol stone in the common bile duct. She had no fever or jaundice.
She underwent endoscopic retrograde cholangiopancreatography (ERCP). A sphincterotomy was performed-cutting the sphincter of Oddi-to widen the duct. A balloon catheter extracted the stone. The procedure took 45 minutes. She recovered within 24 hours and resumed normal diet the next day.
The stone was removed intact and sent for analysis. Microscopic examination confirmed it was composed of 95% cholesterol with trace calcium. It measured 7.2 mm × 5.1 mm.
If a stone fails to pass, it causes biliary obstruction. Symptoms include persistent pain, fever, jaundice (yellow skin), dark urine, and pale stools. These signs indicate potential complications like cholangitis or pancreatitis.
Medical guidelines recommend ERCP for symptomatic stones in the common bile duct. The procedure removes stones using a catheter and balloon. Success rates exceed 95% in experienced centers. For stones that don't respond, surgical removal of the gallbladder (cholecystectomy) is standard.
I've observed a patient who passed a stone during a routine ultrasound. He reported sudden pain, then relief. The stone was later found in his toilet-small, round, and yellow. It measured 4.5 mm. He had no further episodes in the following year.
When stones block the duct, they can trigger pancreatitis. The NIDDK states that gallstones account for 40% of acute pancreatitis cases. In such cases, immediate ERCP is recommended to prevent organ failure.
Once a stone passes through the sphincter of Oddi, it enters the duodenum-the first segment of the small intestine. From there, it moves through the jejunum and ileum. The intestinal lining absorbs water and electrolytes, but not solid material.
Eventually, the stone exits the body via the rectum and anus. This process takes 2-5 days depending on transit time. The stool may show a small, hard mass. Not all patients notice it-many pass stones without awareness.
For those with recurrent stones, the underlying condition-such as high cholesterol or chronic infection-must be treated. Without addressing root causes, new stones form in 30-50% of patients within five years.