Ultrasound diagnostics of polyps
During a standard ultrasound examination, polyps are visualized as specific growths protruding into the gallbladder lumen. They can vary in shape and size: sometimes appearing as multiple small excrescences, and in other cases as single, larger nodules.
To establish an accurate diagnosis, the radiologist must rely on two key ultrasound signs that differentiate polyps from calculi:
- Absence of an acoustic shadow. While dense gallstones block the passage of ultrasound waves and create a characteristic dark trail behind them, polyps allow ultrasound to pass through unhindered.
- Fixation to the wall. The lesions are firmly adherent to the mucosa. If the patient is asked to roll onto their side or stand up, calculi will shift to the bottom of the gallbladder due to gravity, whereas a polyp will remain in its original place.
Contrast-Enhanced Ultrasound (CEUS)
The use of contrast-enhanced ultrasound (Contrast-Enhanced Ultrasound, CEUS) significantly expands diagnostic capabilities. This technique makes it possible to assess the vascularization (blood supply) of the lesion and the degree of contrast agent uptake.
It is important to keep in mind one diagnostic nuance: although malignant tumors typically show avid contrast enhancement, intensely vascularized polyps may well turn out to be benign. The true nature of the lesion is confirmed exclusively through histological tissue examination performed after surgical removal of the organ — cholecystectomy.
The role of diagnostic imaging in jaundice
Biliary tract disorders are closely associated with the development of jaundice syndrome. The primary objective of diagnostic imaging in such patients is to detect and evaluate as thoroughly as possible any potential obstruction (blockage) of the major bile ducts.
During the examination, the physician must clearly answer three fundamental questions:
- Is there a biliary tract obstruction present?
- At precisely which anatomical level has the blockage occurred?
- What is the etiological cause of this obstruction?
Etiology of obstructive jaundice
The causes leading to impaired bile outflow are broadly divided into malignant and benign. Statistically, neoplastic processes predominate.
Malignant causes account for approximately 65% of all obstruction cases. These include:
- Pancreatic cancer (pancreatic carcinomas) — constitutes the vast majority within this group.
- Cholangiocarcinoma (cholangiocarcinoma).
- Metastatic disease (metastases).
- Gallbladder carcinoma (gallbladder carcinoma).
Benign causes are less common, with 65% of them attributable to choledocholithiasis (choledocholithiasis) — the presence of stones in the common bile duct.
Biliary system imaging algorithm
Diagnostic workup always proceeds from simple to complex. Ultrasound (US) consistently remains the preferred method for the initial assessment of the hepatobiliary zone.
When necessary, baseline ultrasound is supplemented with other, more specific tools in various combinations:
- Computed tomography (CT).
- Magnetic resonance cholangiopancreatography (MRCP).
- Endoscopic ultrasonography (EUS). This is the absolute method of choice when targeted assessment of a distal obstruction level is required.
- Direct cholangiography. This includes endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC). In modern practice, these invasive techniques are used much less frequently for purely diagnostic purposes, ceding ground to non-invasive MRCP.
Briefly: answers to topical questions
What histological types of gallbladder polyps are distinguished?
Two main histological types of gallbladder polyps are distinguished: cholesterol and adenomatous.
- Cholesterol polyps — make up the majority; their sizes typically range from 2 to 10 mm.
- Adenomatous polyps (adenomas) — are less common and can reach sizes of up to 2 cm.
What benign pathologies, aside from choledocholithiasis, can cause obstructive jaundice?
In addition to choledocholithiasis, obstructive jaundice can be caused by various inflammatory conditions, parasitic diseases, and congenital malformations.
- Inflammatory diseases and strictures — pancreatitis (acute or chronic), acute cholecystitis with pericholecystic changes, cholangitis, primary sclerosing cholangitis, acute papillitis, stenosis of the ampulla of Vater, as well as postoperative strictures.
- Other biliary pathologies — Mirizzi syndrome (Mirizzi syndrome), impacted stones of the ampulla of Vater, hemobilia, pancreatic head cysts.
- Congenital malformations — biliary atresia and hypoplasia, choledochal cysts, duodenal diverticula.
- Parasitic infestations — echinococcosis, alveolar echinococcosis, opisthorchiasis, ascariasis.
What is the specific ultrasound appearance of a gallbladder cholesterol polyp?
The ultrasound appearance of a cholesterol polyp is characterized by a small echogenic lesion within the gallbladder lumen.
- Acoustic properties — the lesion produces no acoustic shadow (echogenic non-shadowing).
- Mobility — the polyp is fixed to the wall and does not shift when the patient's body position changes.
What are the main indications for magnetic resonance cholangiopancreatography (MRCP)?
The main indications for magnetic resonance cholangiopancreatography are the diagnosis and evaluation of biliary tract pathologies.
- Biliary obstruction — to confirm presence, determine the level, and identify tumors (mandatory for obstruction at the hepatic hilum for Bismuth classification).
- Choledocholithiasis — the method of choice when stones are suspected, as it has higher accuracy compared to CT.
- Primary sclerosing cholangitis — the method of choice for assessing the diffuse nature of the disease.
- Selection for ERCP — used to select candidates for endoscopic intervention in biliary pancreatitis.
- Developmental anomalies — superior to other methods in evaluating biliary tract anomalies.
How can a benign polyp and gallbladder cancer be differentiated based on contrast enhancement kinetics during CEUS?
It is not possible to differentiate a benign polyp from gallbladder cancer solely based on contrast enhancement kinetics during CEUS. Although the method allows visualization of vascularization, avidly enhancing polyps can be benign. Currently, CEUS is insufficiently reliable for accurately distinguishing between benign and malignant polypoid lesions, despite its ability to detect malignant wall destruction and liver invasion.
To easily tell a polyp from a stone on ultrasound, remember the "Shadow and Sloth" rule: a stone casts a Shadow and rolls around, while a polyp has no shadow and "lazily" stays in one place (fixed to the wall).
Class and exam questions
How to differentiate a gallbladder polyp from a calculus during ultrasound?
Unlike a calculus, a polyp does not form an acoustic shadow on the monitor screen and does not change its position when the patient's posture is altered, as it is firmly fixed to the gallbladder wall.
Does avid contrast enhancement on CEUS mean a polyp is malignant?
No, not always. Benign polyps can also exhibit prominent vascularization and contrast enhancement. A definitive diagnosis is established only after cholecystectomy and histology.
Which imaging modality is considered best for evaluating distal biliary obstruction?
The method of choice in this case is endoscopic ultrasonography (EUS), which allows detailed visualization of the distal ducts from inside the gastrointestinal tract.
What pathology is the most frequent cause of malignant obstructive jaundice?
The vast majority of cases of malignant obstruction of the major bile ducts are caused by pancreatic cancer.
What else to study on this topic
- Methodology and physical principles of contrast-enhanced ultrasound (CEUS)
- Cholecystectomy: indications, surgical approach, and outcomes
- Pancreatic cancer: imaging features
- Magnetic resonance cholangiopancreatography (MRCP) vs. ERCP
- Cholangiocarcinoma: classification and imaging modalities
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