What is the recommended imaging approach to evaluate a suspected gallbladder polyp?

Imaging Approach for Suspected Gallbladder Polyp

Transabdominal ultrasound (TAUS) with optimized technique is the primary and recommended imaging modality for evaluating suspected gallbladder polyps. 1, 2

Initial Imaging Strategy

Primary Modality: Transabdominal Ultrasound

• TAUS should be performed with high-frequency probes, color Doppler (including power Doppler, B-Flow, or microvascular Doppler), and proper patient preparation (fasting to ensure gallbladder distention). 1
• The sensitivity of TAUS for detecting gallbladder polyps is 84% with specificity of 96%. 3
• Key features to document include: polyp size, morphology (pedunculated vs sessile), presence of focal wall thickening (≥4 mm), vascularity on Doppler, and any suspicious features suggesting malignancy. 1

When Initial TAUS is Suboptimal

If the initial ultrasound is technically inadequate (poor visualization, gallbladder not well distended, or polyp not clearly seen):

• Repeat TAUS within 1-2 months with optimized grayscale and color Doppler technique and proper patient preparation. 1, 4, 5

Advanced Imaging for Problem-Solving

When to Use Contrast-Enhanced Ultrasound (CEUS)

CEUS should be the next step when differentiation between tumefactive sludge, adenomyomatosis, and a true gallbladder polyp remains challenging after optimized TAUS. 1, 4

CEUS provides superior characterization through:

• Enhancement patterns: Non-neoplastic lesions show late hypoenhancement compared to liver, while neoplastic lesions show marked early enhancement. 1
• Vascular patterns: Stalk-like central enhancement suggests cholesterol polyp; straight intralesional vessels indicate adenomatous polyps; branching vessels with perfusion defects suggest malignancy. 1
• Dynamic features: Eccentric hyperenhancement with sustained homogeneous enhancement favors adenomatous polyps, while wash-out suggests malignancy. 1

When to Use MRI

MRI should be considered if CEUS is not readily available or accessible. 1, 4

MRI characteristics that aid diagnosis:

• High T1-weighted signal may indicate cholesterol polyps or pigment stones. 1
• Restricted diffusion on diffusion-weighted images suggests malignancy. 1
• Intermediate to high T2 signal intensity is more suspicious for malignancy (benign polyps tend to have low T2 signal). 1
• Enhancement patterns: Malignant neoplasms show early peripheral and sustained enhancement, whereas benign lesions tend to show washout. 1
• MRI can definitively diagnose adenomyomatosis by demonstrating cystic-like Rokitansky-Aschoff sinuses, and can distinguish tumefactive sludge (no enhancement) from vascular lesions. 1, 4

Role of CT

CT has inferior diagnostic accuracy compared to CEUS or MRI for characterizing gallbladder polyps and should not be the primary problem-solving modality. 1, 5

However, CT findings that may be useful include:

• Polyps larger than 15 mm, sessile shape, and identification at unenhanced CT suggest malignancy. 1
• A polyp undetectable at unenhanced CT but pedunculated and visible at enhanced CT represents a benign cholesterol polyp with 90% accuracy. 1

Role of Endoscopic Ultrasound (EUS)

• EUS may be useful in select cases at centers with appropriate expertise, particularly for difficult cases requiring additional characterization. 1, 2
• For differentiating true from pseudo polyps: EUS has sensitivity of 85% and specificity of 90%, compared to TAUS sensitivity of 68% and specificity of 79%. 3
• For differentiating dysplastic polyps/carcinomas from benign lesions: EUS has sensitivity of 86% and specificity of 92%, compared to TAUS sensitivity of 79% and specificity of 89%. 3
• However, there is no statistically significant difference in diagnostic accuracy between TAUS and EUS, and EUS is not routinely recommended as first-line imaging. 3

Critical Pitfalls to Avoid

Do Not Apply Standard Algorithm If:

If there is suspicion for invasive or malignant tumor (wall invasion, concurrent liver masses, malignant biliary obstruction, or pathologic lymphadenopathy at porta hepatis or para-aortic chain), immediately refer to an oncologic specialist rather than following routine polyp surveillance algorithms. 1

Common Mimics to Distinguish:

• Tumefactive sludge: Use higher sensitivity Doppler techniques to differentiate from true polyps; sludge lacks vascularity and may change with patient positioning or on follow-up imaging. 1
• Adenomyomatosis: Look for comet-tail artifact at grayscale imaging or twinkling artifact at color Doppler from intramural cholesterol crystals. 1
• Gallstones: These are mobile, shadowing, and hyperechoic structures. 1

Algorithmic Summary

1. Start with optimized TAUS (with color Doppler and proper patient preparation) 1, 2
2. If technically inadequate or uncertain → Repeat TAUS in 1-2 months with optimization 1, 4
3. If still cannot distinguish tumefactive sludge/adenomyomatosis from polyp → CEUS 1, 4
4. If CEUS unavailable → MRI 1, 4
5. If high suspicion for invasive/malignant tumor → Immediate oncologic referral (do not follow routine algorithm) 1