Gallbladder cholesterol polyp covered by viscous biliary sludge, mimicking T1a carcinoma

What is it about?

A gallbladder polypoid lesion (GPL) identified on non-contrast computed tomography (CT) is typically reported as neoplastic, while a cholesterol polyp (CP) is generally non-visible on non-contrast CT. In contrast, we encountered a GPL that histopathology confirmed as CP with a thick stalk, despite being visible on non-contrast CT. Additionally, the largest polypoid lesion in this case showed a tendency to enlarge. However, MRI revealed no evidence of diffusion restriction in the lesion on DWI. These negative MRI findings neither confirmed an apparent advanced GBC nor completely excluded an early GBC. Conventional transabdominal ultrasound (US) showed the large pedunculated polypoid lesion, measuring 15 mm, with a thick stalk but revealed neither a deep hypoechoic area nor a conically thickened outermost hyperechoic layer. This large pedunculated polypoid lesion demonstrated nearly homogeneous enhancement without dendritic blood flow signals and was smaller compared to the reference image on contrast-enhanced ultrasound (CE-US). Consequently, the US findings also excluded an apparent advanced GBC and instead suggested the possibility of early GBC, leading to the decision to perform a full-thickness laparoscopic cholecystectomy. The excised gallbladder revealed several small black stones, multiple small yellow polyps, and a large yellow polyp covered by black viscous mucus in the fundus. Histopathology revealed multiple cholesterol polyps. Notably, the largest polyp, measuring 15 mm, was covered with mucus containing biliary sludge, and its epithelium showed hypersecretion of mucus.

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Photo by Vincent van Zalinge on Unsplash

Photo by Vincent van Zalinge on Unsplash

Why is it important?

As many GPLs are CPs, whose epithelia typically do not secrete mucus and are not covered with mucus containing biliary sludge, they are generally not detectable on non-contrast CT. Conversely, a GPL identified on non-contrast CT is typically considered indicative of a neoplastic lesion. In this case, the largest gallbladder CP was identified on non-contrast CT because its epithelium exhibited hypersecretion of mucus and was covered with mucus-containing biliary sludge. Additionally, it is crucial to consider why the largest pedunculated polypoid lesion appeared smaller than the reference image on CE-US. The viscous sludge covering the lesion likely accounts for this finding, as it behaves like a sludge ball and does not enhance on CE-US. This explains the discrepancy.

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