Gallbladder adenomas are uncommon gallbladder polyps that, although benign, have a premalignant behaviour. 

Terminology

As the distinction of adenomas and intracholecystic papillary-tubular neoplasms (ICPN) is not entirely clear, with important overlap between both entities, some authors have proposed that all the adenomas over 1 cm should be grouped under the ICPN terminology ^1,4. A note is made that the last WHO classification is from 2010, therefore, proceeding these publications. 

Epidemiology

Adenomas make 4% to 7% of all gallbladder polyps ^1,3. They are incidentally found in about 0.5% of the gallbladder specimens ². 

There is a 2.4:1 female-to-male prevalence ratio ². 

Associations

Increased prevalence of gallbladder and biliary tract adenomas occurs in ^1-3: 

• familial adenomatous polyposis syndrome
  • Gardner syndrome
• Peutz-Jeghers syndrome

Pathology

Macroscopic appearance

They are polypoid structures projecting into the gallbladder lumen usually measuring less than 2 cm in size, and showing either a sessile or pedunculated appearance. In about 10% of the cases, adenomas are multiple ². 

Microscopic appearance 

Gallbladder adenomas are classified in ²:

• tubular adenomas
  • the most common
  • composed by pyloric-type glands: cuboidal or columnar cells containing vesicular or hyperchromatic nuclei and covered by biliary epithelium
  • or by intestinal-type glands: with pseudostratified columnar epithelium covered by biliary epithelium
• papillary adenomas
  • papillary structures lined by cuboidal or columnar cells
• tubulopapillary adenomas
  • subtype characterised when both the tubular glands and the papillary formations each corresponds to more than 20% of the tumour

Radiographic features

There are no reliable imaging features to distinguish adenomas from gallbladder adenocarcinomas ^1,3. They might be associated with gallstones or features of chronic cholecystitis. 

Ultrasound

Adenomas are usually solitary gallbladder wall lesions that can have a sessile, pedunculated, or polypoid appearance.

• usually hypoechoic with no posterior acoustic shadowing
• variable size, usually between 5 mm to 20 mm ¹
• may have a lobulated or cauliflowerlike contour ²
• in the pedunculated lesions, the stalk might be difficult to visualise and might require changes in the patient decubitus 
• internal vascularity at colour Doppler may be demonstrated ^3​
• focal gallbladder wall thickening adjacent to the polyp is a worrisome feature concerning for malignancy ²
• CEUS: enhancement is seen in the arterial phase ¹

CT

They might be distinguished as small hypodense intraluminal gallbladder lesions that demonstrate enhancement ³. 

Treatment and prognosis 

Gallbladder adenomas are usually managed surgically. Please refer to the parental article on gallbladder polyps for guidelines on when followup or surgery should be considered.  

Differential diagnosis

• gallbladder adenocarcinoma 
  • virtually impossible to confiently differentiate on imaging alone 
• gallbladder metastasis