Are multiple small polyps less than 1cm on ultrasound consistent with neoplastic or non-neoplastic pathology?

Multiple Small Gallbladder Polyps (<1cm) and Neoplastic Risk

Multiple small gallbladder polyps less than 1cm detected on ultrasound are most likely non-neoplastic in nature, with cholesterol polyps being the most common type in this size range. 1

Risk Stratification Based on Size

• Polyps smaller than 6mm have an extremely low risk of malignancy and generally do not require follow-up if they have typical non-neoplastic features 1
• Polyps measuring 6-9mm have a low risk of malignancy but may warrant limited follow-up depending on their morphology 1
• The risk of neoplasia increases significantly only when polyps reach 10mm or larger 1
• In a survey of Society of Radiologists in Ultrasound (SRU) fellows with an estimated combined experience of 3 million gallbladder ultrasounds, there were no documented cases of malignancy in polyps smaller than 10mm 1

Multiple vs. Single Polyps

• Multiple small polyps are more likely to be non-neoplastic than single polyps 1
• Studies have shown that malignant or neoplastic polyps were more likely to be single rather than multiple 1
• Only two studies showed that a single polyp was an independent risk factor for malignancy at multivariable analysis 1

Natural History of Small Polyps

• Small polyps (<1cm) frequently demonstrate dynamic changes in size over time, with fluctuations of 2-3mm considered part of their natural history 1
• Many small polyps show growth of up to 2-3mm over time without developing malignancy 1
• Some studies have shown non-neoplastic polyp growth rates ranging from 0.16mm/year to 2.76mm/year 1
• In a long-term study by Szpakowski and Tucker, 507 polyps initially smaller than 10mm grew to 10mm or larger, yet none were associated with malignancy in 1549 person-years of follow-up 1

Special Considerations

• In patients with primary sclerosing cholangitis (PSC), gallbladder polyps ≥8mm carry a higher risk of malignancy and should be managed more aggressively 1
• Rapid growth (defined as ≥4mm increase within 12 months) may indicate increased risk of malignancy and warrants surgical consultation 1
• Polyp morphology (sessile vs. pedunculated) is more important than vascularity in determining risk 1

Recommendations for Multiple Small Polyps (<1cm)

• For multiple polyps <6mm with typical non-neoplastic features (especially if they appear as pedunculated "ball-on-the-wall" lesions), no follow-up is generally required 1
• For multiple polyps 6-9mm with low-risk features, follow-up ultrasound at 12 months is recommended 1
• If any polyp shows rapid growth (≥4mm within 12 months) or reaches 15mm, surgical consultation is recommended 1

Pitfalls to Avoid

• Do not rely on polyp vascularity to determine neoplastic potential, as both neoplastic and non-neoplastic polyps can demonstrate internal vascularity on Doppler imaging 1, 2
• Avoid overinterpreting small changes in polyp size (2-3mm), as these fluctuations are part of the natural history of benign polyps 1
• Do not assume that growth to 10mm automatically indicates malignancy, as studies have shown that many polyps that grow to this size remain benign 1

While the evidence strongly suggests that multiple small polyps <1cm are predominantly non-neoplastic, appropriate follow-up based on size, morphology, and growth rate remains important for optimal patient management.