Gallbladder polyp

Gallbladder polyps are commonly occurring elevated lesions on the mucosal surface of the gallbladder. The vast majority are benign.

They are best characterised on ultrasound as a non-shadowing endophytic growth into the gallbladder lumen. 

Epidemiology

Gallbladder polyps are relatively frequent, seen in up to 9% of the population ^1,7,12,14. 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. 

Asymptomatic gallbladder polyps do not seem to raise the risk of gallbladder cancer¹⁹. Polyp frequency is the same in those with gallbladder cancer and those without. Gallbladder cancer has equal incidence in those with polyps and those without. Benign polyps may demonstrate annual growth of around 2mm. There is no evidence for malignant degeneration of polyps. Most malignant polyps are > 20mm.

Clinical presentation

Typically gallbladder polyps are incidental findings in about 10% of upper abdominal ultrasound examinations. Unless large, polyps are 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 ^3,7,14
  • inflammatory polyps: ~10% ¹⁴
  • other rare entities (see benign tumours and tumour-like lesions of the gallbladder)
• neoplastic polyps, (2019 WHO Classification of Tumours, 5th edition, Digestive System Tumours):
  • Intra-cholecystic papillary neoplasms (ICPN) which account for 6% of gallbladder carcinomas and have a favourable survival rate. Mass-forming, endophytic, non-invasive epithelial neoplasms of the mucosa >10mm. There are 4 types: biliary, gastric, intestinal and oncocytoma.
  • pyloric gland adenomas, present in <0.5% of cholecystectomy specimens may be associated with familial adenomatous polyposis or Peutz-Jeghers syndrome.
• malignant polyps: 5% of all polyps. Most measure >20mm.
  • adenocarcinoma: ~90% of malignant polyps
  • and other rare entities including
    • metastases to gallbladder
    • squamous cell carcinoma
    • angiosarcoma

Associations

Patients with Peutz-Jeghers syndrome and Familial Adenomatous Polyposis have an increased prevalence of pyloric gland 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. 

Neoplastic polyps are larger, mean size of 18-21mm compared to non-neoplastic polyps, mean size of 4-7.5mm ¹⁸.

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 the gallbladder lumen, which is usually immobile unless there is a relatively long pedunculated component.

General features of polyps include ⁸:

• small size 
  • cholesterol polyps are the most frequent, over 90% are <10 mm, and the vast majority are <5 mm. They often have a single supplying vessel
  • benign neoplasms or malignant lesions tend to be larger
• echogenicity varies with the 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

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

High-resolution ultrasound 

Some publications have suggested a useful role in high-resolution ultrasound (HRUS) for categorisation of gallbladder polyps with features favouring neoplastic polyps from benign comprising of ¹⁶:

• size >1 cm
• lobulated surface contour
• presence of branching vessels seen on colour Doppler
• hypoechoic internal echo of the polyp
• hypoechoic foci within the polyp

CEUS demonstrates vascular characteristics.

CT

CT is often unable to detect small gallbladder polyps. Larger polyps will appear as soft tissue attenuation projections into the lumen of the gallbladder 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

Society of Radiologists in Ultrasound guidelines (2021)¹⁷

The SRU reviewed current evidence and found no link between gallbladder carcinoma and polyps. Most gallbladder cancers arise from flat dysplastic epithelium that thickens as the cancer progresses. They recognise three categories of polyp: non-neoplastic, benign neoplastic and malignant. The follow-up period is shortened to three years. Concerning growth is increased to > 4mm per annum. Slow growth of benign polyps up to 2mm per annum is common, and conversely, many small polyps disappear! Most malignant polyps are >20mm. Primary sclerosing cholangitis is an important risk factor for cholangiocarcinoma and gallbladder cancer.

They propose the following guidelines:

• Extremely low-risk polyps, i.e. pedunculated ball-on-the-wall or thin stalk:
  • <9 mm: no follow-up (FU)
  • 10-14 mm: FU at 6, 12 and 24 months
  • > 15 mm: surgical consult
• Low-risk polyps, I.e. pedunculated with a thick or wide stalk, or sessile:
  • < 6 mm: no follow-up
  • 7-9 mm follow-up ultrasound at 12 months
  • 10-14 mm:  follow-up ultrasound at 6, 12, 24, and 36 months vs surgical consult
  • > 15 mm: surgical consult
• Intermediate risk: focal wall-thickening >4mm adjacent to polyp:
  • < 6 mm: FU US at 6, 12, 24, 36 months vs surgical consult 
  • > 7 mm: surgical consult

European guidelines (2017)

In 2017 joint guidelines between the European Society of Gastrointestinal and Abdominal Radiology (ESGAR), European Association for Endoscopic Surgery and other Interventional Techniques (EAES), International Society of Digestive Surgery - European Federation (EFISDS) and European Society of Gastrointestinal Endoscopy (ESGE) were published and provide the most up to date and comprehensive guidance ¹³:

• polyp >10 mm: increased risk of malignancy, cholecystectomy recommended
• polyp <10 mm
  • symptoms attributed to the gallbladder: cholecystectomy is suggested if no other cause for the symptoms is determined (polyp may be indicative of underlying occult calculus or inflammation)
  • if the patient has risk factors* for gallbladder malignancy:
    • polyp <6 mm
      • follow-up ultrasound at 6 months, then yearly for 5 years
      • an increase in size ≥2 mm: consider cholecystectomy
    • polyp >6 mm: consider cholecystectomy
  • no risk factors for gallbladder malignancy:
    • polyp <6 mm: follow-up ultrasound at 1, 3 and 5 years
    • polyp >6 mm:
      • follow up ultrasound at 6 months, then yearly for 5 years
      • an increase in size ≥2 mm: consider cholecystectomy

*Risk factors: >50 years, primary sclerosing cholangitis, Indian ethnicity, sessile polyp (including focal wall thickening >4 mm) 

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 progress to cancer ¹⁰.

American College of Radiology guidelines (2013)

According to the White Paper of the ACR Incidental Findings Committee II on Gallbladder and Biliary Findings (2013) ¹¹:

• ≤6 mm: no further evaluation or follow-up necessary ^6,10
• 7-9 mm: yearly follow-up with an ultrasound to ensure no interval growth ¹⁵
• ≥10 mm: surgical consultation for cholecystectomy
  • if no cholecystectomy, annual follow-up is justified ¹¹

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

Differential diagnosis

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

• gallstones
  • usually mobile, but can be adherent
  • usually cast an acoustic shadow
• biliary sludge
  • tumefactive sludge
• adenomyomatosis
• gallbladder carcinoma
• gallbladder metastases (especially in patients with a history of melanoma)
• gallbladder fold, if inadequately distended