How to differentiate an ovoid calcification from a gallbladder polyp?

Differentiating Ovoid Calcification from Gallbladder Polyp

The key to distinguishing an ovoid calcification (gallstone) from a true gallbladder polyp is mobility and acoustic shadowing: gallstones are mobile, hyperechoic structures that produce posterior acoustic shadowing, while true polyps are fixed, non-mobile, non-shadowing protrusions from the gallbladder wall. 1

Primary Distinguishing Features

Gallstones (Ovoid Calcifications)

• Mobility: Gallstones change position with patient repositioning, rolling to the dependent portion of the gallbladder 1
• Acoustic shadowing: Produce characteristic posterior acoustic shadowing due to their solid, calcified nature 1
• Hyperechoic appearance: Appear as bright, echogenic structures on ultrasound 1
• No vascular flow: Completely avascular on Doppler imaging 1

True Gallbladder Polyps

• Fixed position: Remain attached to the gallbladder wall regardless of patient positioning 1
• Non-shadowing: Do not produce posterior acoustic shadowing 1
• Wall attachment: Arise directly from the gallbladder mucosa, either pedunculated (with a stalk) or sessile (broad-based) 1
• "Ball-on-the-wall" appearance: Pedunculated polyps may appear rounded or ovoid but remain barely attached to the wall, simulating a ball resting on a flat surface 1

Critical Pitfall: Tumefactive Sludge

A major diagnostic challenge is tumefactive sludge ("sludge ball"), which can mimic both gallstones and polyps. 1

Distinguishing Tumefactive Sludge

• Partial mobility: May show some movement but less than typical gallstones 1
• No acoustic shadowing: Unlike gallstones, does not produce posterior shadowing 1
• Echogenic but non-vascular: Appears echogenic but shows no internal vascularity 1
• Advanced imaging needed: If unable to distinguish on standard ultrasound, contrast-enhanced ultrasound (CEUS) or MRI can differentiate vascular polyps from avascular sludge 1, 2

Optimized Imaging Technique

When the distinction remains unclear on initial imaging:

• Repeat ultrasound in 1-2 months with optimized technique including proper patient preparation (fasting to ensure gallbladder distention) and high-quality grayscale plus color Doppler imaging 1
• Enhanced Doppler techniques: Power Doppler, B-Flow, or microvascular Doppler can help differentiate true polyps (which may show internal vascularity) from tumefactive sludge 1
• Patient positioning: Multiple patient positions during scanning help confirm mobility of gallstones versus fixed nature of polyps 1

Additional Distinguishing Features

Adenomyomatosis Mimicking Polyps

• Focal adenomyomatosis can appear as a polypoid mass but shows characteristic comet-tail artifacts on grayscale imaging or twinkling artifacts on color Doppler due to intramural cholesterol crystals 1, 2
• Rokitansky-Aschoff sinuses may appear as small intramural cysts 1, 2

Size and Number Considerations

• True polyps average 4-7.5 mm for benign lesions and 18-21 mm for neoplastic lesions 1
• Multiple small lesions are more likely to represent cholesterol polyps (benign) 1
• Single sessile lesions carry higher malignancy risk and warrant closer evaluation 3, 4

Management Based on Differentiation

Once confirmed as a true polyp (not a gallstone):

• ≥10 mm: Cholecystectomy recommended 3
• 6-9 mm with risk factors (age >60, sessile morphology, PSC history, Asian ethnicity): Cholecystectomy recommended 3
• 6-9 mm without risk factors: Ultrasound follow-up at 6 months, 1 year, and 2 years 3
• ≤5 mm without risk factors: No follow-up required 3