Liver

Question 1

Answer 1

Bile Duct Adenoma

Closely packed array of medium-sized glands in a dense, hyalinized stroma without back-to-back gland growth is characteristic of bile duct adenoma. These are usually small, subcapsular, and well-circumscribed, unlike metastases, which may be larger and have infiltrative borders.

Question 2

Answer 2

Biliary Adenofibroma

Complex network of tubuloacinar glands within a fibrous stroma, often containing multiple cystically dilated glandular structures of various sizes.

Malignancies arising from a biliary adenofibroma will display complex papillary, cribriform, and back to back architecture, often with eosinophilic cytoplasm with apocrine features including snouts and decapitation secretions.

Question 3

Answer 3

von Meyenburg complex (bile duct malformation), aka bile duct hamartoma

Composed of dilated, irregularly anastomosing bile ducts with bland cuboidal epithelium embedded in collagenous stroma. Usually small (less than 1.0 cm) and incidental. Bile ducts may contain inspissated bile or eosinophilic debris.

The bile duct malformation (or ductal plate malformation) should be differentiated from the bile duct adenoma by the irregular shapes and dilated regions within the former (contrasting with regular medium-sized, nonpleomorphic glands in the latter).

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Question 4

Answer 4

Fibrolamellar Hepatocellular Carcinoma

Rare type of liver carcinoma that affects teens and young adults.

Histologically has some distinguishing features, including layered fibrolamellar fibrosis, relatively low N:C ratio, abundant cytoplasm, pale bodies (shown, red arrow), hyaline bodies (shown, black arrow).

Molecular: Caused by the DNAJB1::PRKACA fusion

IHC: HepPar and Glypican positivity, indicating hepatic origin. Unlike most HCC, FLC HCC is CK7+ and CD68+.