Gallbladder Polyps

Published on 19/07/2015 by admin

Filed under Radiology

Last modified 22/04/2025

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Large polyps may show internal color flow vascularity

“Comet tail” artifacts suggest cholesterol polyp

• CT: Useful for staging in larger polyps where ↑ risk of malignancy

Difficult to visualize many polyps on CT due to lower spatial resolution

Can show variable enhancement; no convincing correlation between enhancement and malignancy

Useful for staging in larger polyps where ↑ risk of malignancy

TOP DIFFERENTIAL DIAGNOSES

• Tumefactive sludge

• Gallstone

• Polypoid GB carcinoma

• GB metastases

• Adenomyomatosis

PATHOLOGY

• Classification

Neoplastic: Adenoma, adenoma-carcinoma, miscellaneous (fibroma, lipoma, etc.)

Nonneoplastic: Cholesterol polyp, adenomyoma, inflammatory polyp, choristoma

CLINICAL ISSUES

• Size is most important predictor of malignancy

100% of polyps > 20 mm are malignant

43-77% of polyps 10-20 mm are malignant

94% of benign polyps are < 10 mm

• Risk factors for malignancy: Age > 60, gallstones, coexistence of primary sclerosing cholangitis (PSC)

• Reassuring factors: Stability over time, multiple polyps, pedunculated (versus sessile) morphology

• Current recommendations

Cholecystectomy if patient is symptomatic or has cholelithiasis or PSC (regardless of polyp size)

Polyp > 18-20 mm: Open cholecystectomy

Polyp 10-20 mm: Laparoscopic cholecystectomy

Polyp 6-9 mm: Serial follow-up at 3, 6, and 12 months

Polyp ≤ 5 mm: Serial imaging (no consensus; malignancy is extremely rare and some advocate no follow-up)

(Left) Ultrasound of a 43-year-old woman with right upper quadrant pain shows mild gallbladder (GB) wall thickening and multiple small (< 5 mm), slightly echogenic polyps . An elective laparoscopic cholecystectomy for presumed biliary colic revealed cholesterolosis and cholesterol polyps.

(Right) Ultrasound image shows multiple polyps in the GB that measure < 1 cm in size. While the data suggests nodules < 1 cm harbor a very low risk of malignancy, most society guidelines suggest imaging follow-up.

(Left) Ultrasound of a 41-year-old man with chest pain shows two 4-mm GB polyps . Their small size, echogenicity, multiplicity, and stability at follow-up sonography indicate hyperplastic (cholesterol) polyps.

(Right) Ultrasound of a 47-year-old woman shows a 1-cm, pathologically confirmed adenomatous polyp . The likelihood of neoplasia increases with polyp size, but most GB polyps are hyperplastic.

TERMINOLOGY

Definitions

• Polypoid or sessile mass protruding from gallbladder (GB) mucosa

IMAGING

General Features

• Best diagnostic clue

Nonmobile hyperechoic mass protruding from GB mucosa without acoustic shadowing

• Location

GB lumen

• Morphology

Sessile or pedunculated

Imaging Recommendations

• Best imaging tool

Ultrasound; endoscopic ultrasound (EUS)

• Protocol advice

Grayscale and color Doppler US with 6 MHz transducer

CT Findings

• Often difficult to visualize on CT due to lower spatial resolution

CT underestimates polyp size compared to US

• Best visualized on CECT due to vascularity of polyp

Can show variable enhancement

No convincing evidence that polyp enhancement pattern predicts malignancy

• Ill-defined margins of larger polyps possible predictor of malignancy

• Useful for local staging (including lymph node metastases, liver invasion, metastases) in larger polyps where risk of malignancy is high

Ultrasonographic Findings

• Ultrasound is insensitive (only 50%) for polyps, detecting only 1/2 of polyps found at histopathology

• False-positive rate of up to 30%, with positive predictive value of only 10% (compared to histopathology)

Poor accuracy rates for polyps < 5 mm

Potentially due to stones, GB folds, sludge, or cholesterolosis mimicking polyps

Roughly 10% of polyps disappear on follow-up ultrasounds

– Original polyp may have been spurious, but could also reflect polyps breaking off or resolution of inflammatory polyps

• Immobile echogenic mucosal excrescence/nodule, either sessile or lobulated

No acoustic shadowing, unlike stones

Highly echogenic foci or “comet tail” artifacts within polyp suggests a cholesterol polyp

Large polyps may show internal vascularity on color Doppler US

No clear sonographic features to differentiate benign and malignant polyps

– Questionable link between sessile morphology and malignancy

– Multiple nodules more likely to be benign (usually cholesterol polyps); neoplastic polyps often solitary

• EUS has been shown to have higher accuracy in differentiation of benign (97%) vs. malignant (76%) polyps

Better demonstration of mucosal invasion

Nuclear Medicine Findings

• PET/CT

GB carcinoma has avid FDG uptake (relative to liver)

Some studies suggest role of PET in malignancy risk stratification of polyps 10-20 mm

DIFFERENTIAL DIAGNOSIS

Tumefactive Sludge

• Focal collection of sludge (cholesterol or calcium bilirubinate crystals) appearing polypoid or mass-like

• No acoustic shadowing or internal flow on color Doppler imaging

• Sludge will slowly move when altering patient position during scanning

Gallstone

• Posterior acoustic shadowing

• “Twinkling” artifact with color Doppler US

• Freely mobile within GB unless impacted

Polypoid GB Carcinoma

• Typically larger than adenoma, most often > 15 mm

• May cause focal loss of wall reflectivity due to mural invasion

• Internal flow often detectable with color Doppler US

• Porta hepatis adenopathy &/or direct liver invasion

• Often associated with stones

GB Metastases

• Melanoma most common

• Enhancing polypoid mass in setting of widespread metastatic disease

Adenomyomatosis

• Can be nodular and mass-like, but usually associated with “comet-tail” artifact

PATHOLOGY

General Features

• Etiology

Unknown

• Genetics

GB adenomas associated with familial adenomatous polyposis and Peutz-Jeghers syndrome

Staging, Grading, & Classification

• Neoplastic polyps

Adenoma

– Benign

– Accounts for 0.5-4% of polyps

– Solitary, usually in range of 5-20 mm

– Often associated with gallstones

– Progression to adenocarcinoma is yet unclear; adenoma-carcinoma sequence seen in colon cancer has not been defined for GB

Not clear that GB cancers arise from adenomas

Adenocarcinoma

– 15-25% of GB adenocarcinomas present as polypoid lesions

– Solitary, usually > 1 cm (in 1 study 88% were > 1 cm)

– May have thickened implantation base or evidence of mucosal invasion

Rare benign lesions: Leiomyoma, lipoma, neurofibroma, carcinoid

Rare malignant lesions: Squamous cell carcinoma, mucinous cystadenocarcinoma

• Nonneoplastic polyps

Majority (> 95%) of cases

Cholesterol polyps

– 1/3 of cases in cholesterolosis are polypoid, the rest manifest as diffuse nodularity of GB

– Accounts for 60% of all polyps

– Infiltration of mucosa and lamina propria with lipid-laden foamy macrophages

– Multiple, < 10 mm

Adenomyomatosis

– Localized (focal) adenomyomatosis can mimic polyps

– Accounts for 25% of polyps

– Usually seen in fundus, usually 10-20 mm

– Excessive epithelial proliferation with invagination into muscular layer

Inflammatory polyps

– Accounts for 10% of polyps

– Result from granulation and fibrous tissue secondary to chronic inflammation

– Sessile or pedunculated, usually < 10 mm

Choristoma (rare): Heterotopic gastric, pancreatic, or hepatic tissue

Microscopic Features

• Adenomas may be tubular, papillary, or tubulopapillary

Tubular adenoma most common variant

– Covered with biliary epithelium, composed of pyloric or intestinal-type glands

Papillary adenomas

– Papillary structures lined by cuboidal or columnar cells

Tubulopapillary adenomas are composite of both

• Cholesterol polyp composed of sheets of lipid-laden macrophages with normal overlying GB mucosa

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

Most are asymptomatic

• Other signs/symptoms

Debatable association with chronic dyspepsia

Cholesterol polyps can detach and behave like stones

– Can cause biliary colic, obstruction, pancreatitis

Lab markers: CEA and CA19-9 have no role in differentiating benign and malignant polyps

Demographics

• Epidemiology

Prevalence varies by demographics of studied population

– 1.5-5% in abdominal ultrasounds

– 0.005-13.8% of resected GBs

No consistent relationship with age, gender, or obesity

1 study showed inverse relationship with stones

– May be harder to diagnose polyps in presence of cholelithiasis

Natural History & Prognosis

• Natural history and management of polyps has been an area of great debate, with no management consensus

• Large prospective study of incidental polyps < 10 mm showed no change in size in 2- and 5-year follow-ups

• Retrospective study of 346 incidental polyps demonstrated growth in only 1% of cases; no lesions < 6 mm were neoplastic

• Risk factors for malignancy

Proposed risk factors for malignancy include: Age > 60 years, gallstone, coexistence of primary sclerosing cholangitis (PSC), and irregular GB wall thickening or sessile morphology of polyp on US

– Other concerning features: Irregular GB wall thickening and sessile morphology of polyp

Size is most useful predictor of malignancy

– 100% of polyps > 20 mm are malignant (either invasive carcinoma or high-grade dysplasia)

– 43-77% of polyps 10-20 mm are malignant

– 94% of benign polyps are < 10 mm; 88% of malignant polyps are > 10 mm

– Although older studies suggested a cut-off value of 10 mm for safely differentiating benign from malignant polyps, some studies propose changing cut-off to 6 mm for reaching 100% sensitivity (albeit in cost of lower specificity)