Pain under the right ribs after a rich meal. Bloating that comes and goes. A report from another scan that mentions “gallbladder sludge” or “a 5 mm polyp.” The gallbladder is one of the most common reasons people end up having an abdominal ultrasound, and it is also the organ ultrasound sees best: for gallstones, it is the gold-standard test, more accurate than CT.
This guide explains why you have to fast, what the sonographer looks for, what the common findings (stones, sludge, polyps, wall thickening) actually mean, which ones matter, and what usually happens next.
Why gallbladder ultrasound needs an empty stomach
The gallbladder is a small pouch under the liver that stores bile. Between meals it fills up, stretching into a thin-walled sac of fluid that ultrasound sees beautifully: any stone inside stands out as a bright spot against the black fluid. The moment you eat, especially fat, the gallbladder squeezes and empties. A contracted gallbladder is small and thick-walled, stones can hide in the folds, and the wall thickness cannot be judged. That is why the instruction is nothing to eat for eight hours before the scan (water and your usual medications are fine). Coffee, gum and smoking also make it contract, so skip those too. Our preparation guide covers the details.
What the sonographer looks at
A gallbladder study is usually part of a right-upper-quadrant or complete abdominal ultrasound. You lie on your back and then on your left side, and you will be asked to take deep breaths and hold them, which pushes the liver and gallbladder down from behind the ribs. The sonographer records:
- The gallbladder itself: its size, whether the wall is thin (normally 3 mm or less), and whether there is fluid around it.
- Its contents: stones, sludge, polyps or anything attached to the wall. Stones are confirmed by tilting you to see whether they roll.
- Tenderness: if pressing the probe directly over the gallbladder reproduces your pain (a “sonographic Murphy sign”), that is recorded; combined with other findings it points toward inflammation.
- The bile ducts: the common bile duct is measured. A widened duct suggests something is blocking bile flow, most often a stone that has escaped the gallbladder.
- The liver, pancreas and right kidney, because pain in this area has other causes, and because a complete abdominal study looks at all of them.
Gallstones: what the report means
Gallstones are extremely common: roughly one adult in ten has them, and the proportion is higher in women, after 40, with obesity, after rapid weight loss, and with a family history. Ultrasound detects them with better than 95 percent accuracy. On the screen a stone is a bright (echogenic) focus that casts a dark shadow behind it, because sound cannot pass through it, and that moves when you change position.
The single most important thing to know: most gallstones cause no symptoms and need no treatment. About four in five people with stones never have trouble from them, and only a small percentage per year go on to develop symptoms. Stones found by chance on a scan done for another reason are usually simply noted. Treatment is considered when stones cause symptoms, which classically means:
- Biliary colic: a steady, often severe ache under the right ribs or in the upper middle of the abdomen, sometimes spreading to the right shoulder blade, typically starting after a meal and lasting from half an hour to several hours before fading.
- Acute cholecystitis: the same pain that does not fade, with fever, nausea and marked tenderness, caused by a stone blocking the gallbladder outlet. This needs same-day medical care.
- A stone in the bile duct: pain with jaundice (yellow skin or eyes), dark urine or pale stools, and sometimes pancreatitis. Also urgent.
When stones are symptomatic, the standard treatment is removal of the gallbladder (cholecystectomy), usually keyhole surgery, and the ultrasound report is what the surgeon uses to plan it.
Sludge
“Sludge” is thickened bile, a slurry of cholesterol crystals and bile pigment that has not formed into stones. On ultrasound it looks like a layer of fine echoes settling in the dependent part of the gallbladder, without the shadow a stone casts. It is common after fasting, during pregnancy, with rapid weight loss or prolonged illness, and it often clears on its own. Sludge can cause the same colicky symptoms as stones and can progress to stones, so if it is found alongside symptoms it is treated much like stones; if it is an incidental finding, it is usually just noted.
Gallbladder polyps
Polyps are small growths on the inner wall, found in several percent of people scanned. On ultrasound they look like a bright spot attached to the wall that does not move and does not cast a shadow, which is how they are told apart from stones. The overwhelming majority, more than nine in ten, are “cholesterol polyps,” which are harmless deposits rather than true growths.
Size is what the radiologist uses to decide follow-up, because the small minority of true adenomas and the rare cancers are almost always larger. A commonly used scheme:
| Polyp size | Usual recommendation |
|---|---|
| 6 mm or smaller | No follow-up needed in most people. |
| 6 to 9 mm | Follow-up ultrasound to confirm it is not growing, at an interval the radiologist states (often 6 to 12 months, then yearly for a few years). |
| 10 mm or larger | Referral to a surgeon to discuss removal of the gallbladder, because the likelihood of a significant lesion rises sharply above this size. |
Guidelines differ slightly in their thresholds and in how long to follow, and they are stricter for people with risk factors (such as primary sclerosing cholangitis). Your report will state the radiologist’s specific recommendation; a polyp that is unchanged across follow-up scans is very reassuring.
Wall thickening
A gallbladder wall thicker than about 3 mm is noted in reports, and people often assume it means infection. In fact the commonest cause of a “thick wall” on a scan is simply that the gallbladder is contracted because you ate. Genuine thickening with pain, fever and tenderness suggests acute cholecystitis, but a thick wall without those also occurs with liver disease, heart failure, low blood protein, fluid in the abdomen and some kidney conditions. In other words, wall thickening is a sign that needs context, which is exactly why the report will say “clinical correlation recommended.”
Other words you may see
- Adenomyomatosis: a benign thickening of the wall with tiny pockets that produce characteristic bright “comet-tail” artifacts. Harmless; no follow-up is usually needed.
- Porcelain gallbladder: calcification of the wall. Uncommon; it is usually referred to a surgeon because of a historical association with cancer, although the risk is now thought to be lower than once believed.
- Hydrops / distended gallbladder: an over-full gallbladder, often because the outlet is blocked.
- Pericholecystic fluid: fluid around the gallbladder, one of the signs of inflammation.
- Choledocholithiasis: a stone in the common bile duct.
- Dilated common bile duct: wider than expected for your age (the normal upper limit is about 6 mm in younger adults, rising with age, and larger after gallbladder removal). It prompts a search for a blockage, often with a specialized MRI called MRCP.
- Contracted gallbladder, limited evaluation: you ate; the study may need to be repeated after a proper fast.
For the general vocabulary (echogenic, shadowing, hypoechoic), see our guide to ultrasound report terms.
When ultrasound is not enough
Ultrasound is the right first test and often the only one needed. Its limits: stones that have moved into the lower bile duct are hard to see because bowel gas gets in the way (MRCP or endoscopic ultrasound sees them); if the scan is normal but symptoms strongly suggest gallbladder dysfunction, a nuclear medicine HIDA scan can measure how well the gallbladder empties; and a CT is used when the question is wider than the gallbladder, such as pancreatitis or a possible abscess. Our article on ultrasound versus CT and MRI explains how doctors choose.
What to do with your result
- Stones or sludge with no symptoms: usually nothing, beyond knowing they are there and recognizing the symptoms above if they ever occur.
- Stones with episodes of pain: see your doctor to discuss surgery; take the report with you.
- A polyp: follow the interval in the report. Keep the report, so the next scan can be compared.
- Pain with fever, jaundice, or pain that will not settle: urgent care or an emergency room, not a routine follow-up.
Booking a gallbladder ultrasound
At UltraVision Imaging, a limited right-upper-quadrant study or a complete abdominal ultrasound can be booked directly without a referral, at our private clinic or at your home. Every study is performed by an ARDMS-certified sonographer and read by a board-certified radiologist, and the written report, including any polyp follow-up recommendation, is typically ready within 24 hours. Enter your ZIP to see times, or call (916) 751-1944. Remember the eight-hour fast.
Frequently asked questions
Why do I have to fast before a gallbladder ultrasound?
Eating, especially fat, makes the gallbladder contract and empty. A contracted gallbladder is small and thick-walled, so stones can hide and the wall cannot be assessed. Fasting for eight hours keeps it full and easy to evaluate. Water and regular medications are fine; skip coffee, gum and smoking.
Can an ultrasound detect gallstones?
Yes. Ultrasound is the best test for gallstones, detecting them with better than 95 percent accuracy. A stone appears as a bright spot that casts a shadow and moves when you change position.
Do gallstones found on ultrasound need to be removed?
Usually not. Most gallstones never cause symptoms and are simply noted. Surgery is considered when stones cause biliary colic (pain after meals), cholecystitis, or a blocked bile duct.
What is gallbladder sludge?
Thickened bile that has not formed stones. It often clears on its own and is frequently an incidental finding, but it can cause the same symptoms as stones and can progress to them.
Is a gallbladder polyp serious?
More than nine in ten are harmless cholesterol polyps. Polyps 6 mm or smaller usually need no follow-up, 6 to 9 mm polyps are rechecked to confirm they are not growing, and polyps 10 mm or larger are referred to a surgeon.
What does gallbladder wall thickening mean?
A wall thicker than about 3 mm. The most common cause is that the gallbladder is contracted after eating. With pain, fever and tenderness it suggests cholecystitis; without them it can reflect liver disease, heart failure, low blood protein or fluid in the abdomen, which is why reports ask for clinical correlation.
How long does a gallbladder ultrasound take?
About 20 to 30 minutes of scanning for a focused right-upper-quadrant study, longer for a complete abdominal ultrasound.
Do I need a referral for a gallbladder ultrasound?
Not at UltraVision Imaging. A limited or complete abdominal ultrasound can be booked directly, and the radiologist’s report is typically ready within 24 hours.
This article is general health information, not medical advice. It does not replace a conversation with your own physician, who knows your history and can interpret results in context. If you have symptoms that worry you, contact your doctor; if you think you are having a medical emergency, call 911.