Gallbladder Polyps and Their Malignant Potential

The word “polyp” describes a projection into the gallbladder lumen before it establishes a biological diagnosis. I need to distinguish that imaging observation from neoplasia, existing cancer, and the future possibility of malignant transformation.

Clinical overview

Most incidentally detected gallbladder polyps are benign, frequently cholesterol pseudopolyps. The clinical problem is to identify lesions that need further characterization, surveillance, or surgery while avoiding intervention for findings with little malignant potential.

Four questions require different evidence: Is there a true attached lesion? Is it neoplastic? Does it already contain malignancy? Will it become malignant later? Ultrasound morphology can inform risk, but a pathology label obtained after surgery cannot by itself validate a prediction of future transformation.

In my research, I would define the target before assembling cases. “Cholecystectomy recommended” is a management outcome influenced by guidelines, symptoms, fitness, and preference. It is not interchangeable with “malignant polyp.”

Anatomy and pathophysiology

Cholesterol pseudopolyps differ from epithelial neoplasms

Cholesterol polyps contain cholesterol-laden macrophages within the mucosal lamina propria. They are non-neoplastic pseudopolyps, not adenomas undergoing an inevitable progression toward carcinoma.

Adenomatous lesions are epithelial neoplasms. Their pathological assessment concerns architecture, dysplasia, and whether invasive carcinoma is present. An adenoma diagnosis does not establish invasion or quantify an individual patient’s future transformation risk.

The SRU consensus discusses updated terminology, including pyloric gland adenoma and intracholecystic papillary neoplasm. I would preserve original pathology wording when reviewing historical datasets and document any category mapping. A broad historical “adenomatous polyp” label may not correspond exactly to a contemporary category.

An imaging projection can arise through other mechanisms

Inflammatory lesions can project into the lumen. Adenomyomatosis is a mural process involving Rokitansky-Aschoff sinuses, which may produce intramural cystic spaces and comet-tail artifacts. Adherent sludge can simulate a soft-tissue projection without being a tissue polyp.

The mechanism matters because similar silhouettes imply different targets. A detector may correctly identify a protrusion while incorrectly treating it as a neoplasm. I read this as a reason to retain an “indeterminate polypoid finding” category when imaging cannot establish the lesion’s nature.

Diagnostic workflow and imaging findings

Establish that a lesion is attached

The examination should demonstrate the finding in more than one plane, assess its relationship to the wall, and test positional behavior. A typical polyp remains attached and does not produce the clean posterior shadow expected from many stones.

These features are imperfect. An impacted stone can remain fixed, and adherent sludge can resist immediate redistribution. Detectable internal vascularity supports tissue, but absent Doppler flow does not exclude a small polyp. Yu and colleagues describe these diagnostic overlaps.

In a hypothetical case, a nonshadowing echogenic nodule appears fixed along the posterior wall. A short positional comparison does not establish histology. I would seek reproducible attachment, inspect the surrounding wall, optimize flow detection when useful, and preserve uncertainty if sludge remains plausible.

Measure a reproducible anatomical quantity

The 2025 KSAR recommendations specify the longest diameter across multiple views, measured outer margin to outer margin. Their convention includes a stalk when part of that longest dimension and excludes adjacent wall thickening.

I would record the lesion’s location and morphology so that follow-up measures the same lesion. In a gallbladder with several polyps, comparing whichever lesion appears largest on each examination can manufacture an apparent trajectory.

Pixel length alone is inadequate after resizing. Physical scale must be retained if a model is expected to use millimeters. Calipers can communicate size, but they also expose operator behavior and may directly encode a management threshold.

Describe morphology without assigning histology

A pedunculated lesion has a stalk; a sessile lesion has a broad attachment. Adjacent focal wall thickening is a separate observation from polyp diameter. Echogenicity, internal heterogeneity, and vascularity should also remain separate descriptors.

An echogenic lesion is not automatically a cholesterol polyp, and a sessile lesion is not automatically cancer. The diagnostic issue is how findings combine with size and context, including whether the apparent wall abnormality could be explained by contraction, edema, or adenomyomatosis.

Separate growth from measurement variation

For measurements \(d_1\) and \(d_2\) obtained at times \(t_1\) and \(t_2\), an average measured growth rate is

\[g=\frac{d_2-d_1}{t_2-t_1}.\]

With diameter in millimeters and time in years, \(g\) has units of mm/year. This summarizes two observations; it does not show whether growth was continuous or whether the difference exceeds measurement error.

Lee and colleagues evaluated repeatability using intraclass correlation coefficients and Bland-Altman limits of agreement. I take their work as a reason to examine absolute disagreement as well as correlation. Two readers can rank lesions similarly while disagreeing enough to move an individual lesion across a management cutoff.

Differential diagnosis and management context

Thresholds belong to named frameworks

The 2022 European joint guideline recommends cholecystectomy for lesions at least 10 mm when the patient is fit for and accepts surgery. For 6–9 mm lesions, risk factors include age over 60 years, primary sclerosing cholangitis, Asian ethnicity, and sessility, including focal wall thickening greater than 4 mm.

For 6–9 mm lesions without those risk factors, or lesions no larger than 5 mm with risk factors, it recommends ultrasound at six months, one year, and two years, stopping if there is no growth. Lesions no larger than 5 mm without risk factors do not require follow-up under that framework.

The SRU recommendations stratify incidental polyps by morphology. Surgical consultation is recommended at 15 mm for extremely low-risk and low-risk categories. The indeterminate category, including unexplained adjacent focal wall thickening of at least 4 mm, has a lower consultation threshold of 7 mm. Its algorithm excludes patients with primary sclerosing cholangitis.

The 2025 KSAR recommendations recommend cholecystectomy in surgically fit patients at 15 mm or above, or at 10–14 mm with concerning features: sessility, adjacent wall thickening, or significant growth. At 10–14 mm without those features, surgery or surveillance is an option.

I would name the framework whenever reporting a recommendation. Combining one guideline’s size threshold with another’s risk factors creates an unvalidated rule.

Growth does not establish malignant transformation

In the longitudinal cohort of Szpakowski and Tucker, small polyps commonly increased in measured size, while gallbladder cancer remained uncommon. The study provides natural-history evidence beyond surgically selected cases.

I would distinguish detection of cancer soon after initial imaging from demonstrated transformation of a previously benign lesion. An initially unrecognized cancer and a benign lesion that later becomes malignant are different biological histories, even if both appear in a follow-up dataset.

A hypothetical lesion measured just below and then just above a cutoff requires review of comparable planes, scale, and boundaries. Crossing the cutoff changes a management category; it does not prove that tissue biology changed abruptly.

Suspicious invasion changes the clinical question

Wall disruption, a mass extending into adjacent liver, or other evidence of invasive disease requires evaluation as suspected cancer rather than routine small-polyp surveillance. Symptoms also need independent assessment because an incidental polyp may not explain pain.

I read the management context as a balance between the risk of missing consequential disease and the burdens of surgery and surveillance. The imaging report should make the supporting observations available for that decision.

Implications for medical AI

Pathology-confirmed datasets are selected by the decision to operate. Large, suspicious, symptomatic, or growing lesions are more likely to receive histological verification. A classifier evaluated only in that group estimates performance among operated patients, not necessarily among all incidentally detected polyps.

I would retain separate reference categories for pathology, longitudinal imaging, and unresolved follow-up. Stability on surveillance is informative, but it does not provide the same histological answer as resection. Loss to follow-up should not become a benign label.

A feasible audit could compare an image model with a size-only baseline within overlapping size ranges. If the model adds discrimination, I would examine whether the improvement tracks independently assessed attachment and adjacent wall findings or documentation cues.

A second question is whether repeated reader measurements change the apparent advantage over guideline baselines. I would recompute categories using each reader’s measurements and report threshold disagreement, rather than treat one caliper value as exact ground truth.

Third, paired marked and unmarked exports could test whether predictions depend on calipers after physical image scale is preserved. Removing scale entirely would make this comparison ambiguous because size is legitimate evidence.

Finally, I would separate prediction of current malignant histology from prediction of future cancer. The latter requires a defined starting population, time horizon, and outcome ascertainment. A still-image dataset assembled at surgery cannot supply those missing temporal relationships.

References

• Kamaya et al., Management of Incidentally Detected Gallbladder Polyps: Society of Radiologists in Ultrasound Consensus Conference Recommendations, Radiology 2022.
• Foley et al., Management and follow-up of gallbladder polyps: updated joint guidelines between the ESGAR, EAES, EFISDS and ESGE, European Radiology 2022.
• Chang et al., Interpretation, Reporting, Imaging-Based Workups, and Surveillance of Incidentally Detected Gallbladder Polyps and Gallbladder Wall Thickening: 2025 Recommendations From the Korean Society of Abdominal Radiology, Korean Journal of Radiology 2025.
• Yu et al., Benign gallbladder diseases: Imaging techniques and tips for differentiating with malignant gallbladder diseases, World Journal of Gastroenterology 2020.
• Lee et al., Intraobserver and interobserver reliability in sonographic size measurements of gallbladder polyps, European Radiology 2020.
• Szpakowski and Tucker, Outcomes of Gallbladder Polyps and Their Association With Gallbladder Cancer in a 20-Year Cohort, JAMA Network Open 2020.