Gallbladder polyp

Gallbladder polyps are elevated lesions on the mucosal surface of the gallbladder. The vast majority are benign, but malignant entities are possible. Gallbladder polyps may be detected on ultrasound, CT, or MRI, but are usually best characterized on ultrasound.

Epidemiology

Gallbladder polyps are relatively frequent, seen in up to 7% of the population ^1,7,12. Over 90% are benign, and the majority are cholesterol polyps.

Cholesterol polyps are most frequently identified in patients between 40-50 years of age, and are more common in women (F:M, 2.9:1) ³. 

Clinical presentation

Typically gallbladder polyps are incidentally found on upper abdominal imaging, usually during imaging for upper abdominal discomfort. In most instances, the polyps are thought to be asymptomatic ^1,3.

Pathology

A wide variety of entities appear as polyps and histology is variable. 

• benign polyps: 95% of all polyps
  • cholesterol polyps: >50% of all polyps ^3,7
  • adenoma: ~30%, possibly premalignant ⁴
  • inflammatory polyps
  • adenomyomatosis
  • other rare entities (see benign tumours and tumour like lesions of the gallbladder)
• malignant polyps: 5% of all polyps
  • adenocarcinoma: ~90% of malignant polyps
  • other rare entities including:
    • metastases to gallbladder
    • squamous cell carcinoma
    • angiosarcoma

Cholesterol polyps appear as yellow, lobulated, and often pedunculated masses.  Histologically, they are composed of lipid-laden macrophages, covered with normal epithelium ³.

Patients with Peutz-Jeghers syndrome have an increased prevalence of adenomas within the gallbladder.

Radiographic features

In most instances predicting histology based purely on imaging is not possible, with the possible exception of cholesterol polyps in some instances (see below), and thus features that are predictive of benign vs malignant disease should be noted (see benign vs malignant features of gallbladder polyps) ^1,6-7. 

Overall size is probably the most useful indicator of malignancy, with polyps over 10 mm in diameter having a malignancy rate of 37-88% ³.

Ultrasound

Ultrasound is the best initial imaging choice, and is often able to separate cholesterol polyps from those requiring treatment. General features of gallbladder polyps are a non shadowing polypoid ingrowth into gallbladder lumen, which is usually immobile unless there is a relatively long pedunculated component.

Features of a cholesterol polyp include ⁸:

• small size 
  • over 90% are <10 mm, the vast majority less than <5 mm
• echogenicity varies with size
  • small polyps are echogenic but non-shadowing
  • larger cholesterol polyps tend to be hypoechoic
• morphology
  • small polyps may be adherent to the wall and smooth
  • larger lesions tend to be pedunculated and granular in outline

Adenomas on the other hand tend to be larger, solitary, more often sessile with internal vascularity, and of intermediate echogenicity. It is not possible to distinguish an adenoma from an adenocarcinoma ^6-8.

Rarely, endoscopic ultrasound may be useful to further assess gallbladder polyps as it may generate higher resolution images ^7-8.

CT

CT is often unable to detect small gallbladder polyps. Larger polyps will appear as soft tissue attenuation projections into the lumen of the bladder, and will demonstrate enhancement similar to that of the rest of the gallbladder. More intense enhancement should be viewed with suspicion, as it is associated with increased vascularity in malignancy.

Treatment and prognosis

Statistically, gallbladder polyps are common and gallbladder cancer is rare, so very few polyps progress to gallbladder cancer. There is also controversy regarding the development of gallbladder cancer and some suggest that polyps may not actually progress to cancer ¹⁰.

Recommended follow-up of small polyps (<10 mm) varies from author to author. A commonly accepted strategy includes:

• ≤5 mm: no further follow up necessary ^6,10
• 6-9 mm: follow-up to ensure no interval growth. Follow-up interval varies from 3 to 6 months ^6,9
• ≥10 mm: surgical consultation
  • usually warrants cholecystectomy
  • if no cholecystectomy, annual follow up is warranted ¹¹

Lower thresholds for follow up or intervention may be warranted if one's patient population is known to have a higher risk of gallbladder carcinoma (e.g. higher incidences in Pakistan, Ecuador, or females in India).

Differential diagnosis

The differential for a gallbladder polyp is limited, and includes ⁶:

• gallstones
  • usually mobile, but may be adherent
  • usually cast an acoustic shadow
• biliary sludge
  • tumefactive sludge
• adenomyomatosis
• gallbladder carcinoma