Ultrasound criteria for shallow T2 extrahepatic cholangiocarcinoma

What is it about?

Ultrasound criteria for shallow T2 extrahepatic cholangiocarcinoma (eCCA) are described. The layer structure of the bile duct through ultrasound or endoscopic ultrasound is as follows: the 1st hyperechoic layer (the innermost hyperechoic layer), the 2nd hypoechoic layer, and the 3rd hyperechoic layer (the outermost hyperechoic layer: OHL) are border echo + mucosa, fibromuscular layer + shallow fibrous subserosa, and deep adipose subserosa + serosa + border echo, respectively. Fibromuscular layer of the bile duct corresponds to muscularis propria of the gallbladder. Consequently, ultrasound criteria for shallow T2 eCCA is consistent with those for shallow T2 gallbladder carcinoma (GBC), replacing muscularis propria with fibromuscular layer. A deep hypoechoic area in eCCA generally corresponds to subserosal invasion associated with abundant fibrosis and lymphocytic infiltration, irrespective of the integrity of the outermost hyperechoic layer, similar to the findings observed in GBC. Because the author does not describe the ultrasonographic diagnosis of the depth of invasion in eCCA with a small deep hypoechoic area, we requested that the author provides a loupe view of the corresponding histopathological specimen to support the findings.

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Photo by Vincent van Zalinge on Unsplash

Photo by Vincent van Zalinge on Unsplash

Why is it important?

In gallbladder tumors, a deep hypoechoic area on ultrasound generally represents subserosal invasion accompanied by abundant fibrosis and lymphocytic infiltration. However, it may also correspond to medullary lesions, hyperplastic lymphoid follicles, or non-neoplastic fibrosis. Therefore, accurate interpretation requires careful correlation between the ultrasonographic and histopathological findings, for which a loupe view of the corresponding histopathological specimen is indispensable. Regarding a deep hypoechoic area in eCCA on ultrasound, accurate interpretation similarly requires careful correlation between the ultrasonographic and histopathological findings. Furthermore, we hypothesize that an eCCA presenting with both a deep hypoechoic area and a thickened OHL suggests shallow T2 invasion, consistent with the criteria established for GBC.

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