What is a Gallbladder Polyp?
A gallbladder polyp is an elevation of the gallbladder mucosa that protrudes into the gallbladder lumen, most commonly detected incidentally on ultrasound imaging. 1, 2
Classification and Types
Gallbladder polyps are divided into two main categories based on their pathologic nature:
Non-Neoplastic (Pseudopolyps) - Most Common
- Cholesterol polyps: The most frequent type, representing the majority of gallbladder polyps, with no malignant potential 3, 1
- Inflammatory polyps: Benign lesions with no cancer risk
- Focal adenomyomatosis: Another benign variant
- These pseudopolyps are associated with impaired cholesterol metabolism and often occur alongside metabolic syndrome 3
Neoplastic (True Polyps) - Less Common
- Benign: Adenomas (most common benign neoplastic type)
- Malignant: Adenocarcinoma
- Only these true neoplastic polyps carry malignant potential 1
Prevalence and Clinical Significance
Gallbladder polyps are found in approximately 3-7% of adults undergoing abdominal ultrasonography 4, though reported prevalence ranges from 0.3% to 13.8% across different populations 3. The critical distinction is that only about 5% of detected polyps are "true" neoplastic polyps with actual malignant potential 2.
Morphologic Features
According to the 2022 Society of Radiologists in Ultrasound guidelines, polyps can be characterized by their appearance 5:
Pedunculated ("Ball-on-the-Wall")
- Attached via a thin stalk or pedicle
- Appears like a ball resting on a flat surface on ultrasound
- Generally associated with lower malignancy risk
- The stalk is rarely visible but may be implied by a single small vessel at the base
Sessile
- Flat or dome-shaped masses with broad-based attachment
- No visible stalk
- Higher association with neoplastic and malignant polyps 5
Key Clinical Pitfall
The major challenge is that non-neoplastic pseudopolyps and neoplastic polyps cannot be reliably distinguished by ultrasound morphology alone 6. This is why size has become the primary predictor used clinically, as it's the most validated risk factor for malignancy across multiple studies 5, 4.
Malignancy Risk Context
The absolute cancer risk in incidentally detected gallbladder polyps remains very low 4. In a large 20-year population study, the incidence of gallbladder cancer in patients with polyps larger than 10 mm was only 0.4% 5. For polyps smaller than 6 mm, the rate was 1.3 per 100,000 patients 5.