Table 1.

Pathology parameters that were assessed

Type of resection	(extended) Hemihepatectomy or external bile duct resection, since resection planes are not identical in these two treatments
Surgical specimen’s orientation marks	As provided by the surgeon: provided or not provided. Orientation marks are usually not provided for the liver parenchyma and periductal dissection plane
The tumor’s gross features	Size in mm
The liver parenchyma’s microscopic features	Inflammation, fibrosis, steatosis, (secondary) sclerosing cholangitis due to obstruction
Tumor’s microscopic features	Histological subtype, differentiation grade, and perineural growth. Vasoinvasive growth was subdivided in major vessel involvement or microscopic vessel involvement. Major vessel involvement was determined as invasion of the lumen of the portal vein and/or hepatic artery. Involvement of only the media was determined as negative involvement, since the biological implications of vessel involvement are mainly dependent on intraluminal tumor growth
Lymph nodes	Total amount of derived lymph nodes and ratio of positive lymph nodes
Frozen sections	Frozen sections of the proximal and distal bile duct resection plane, hepatic artery, portal vein, lymph nodes, and other biopsies or lesions It was noted whether frozen sections were concordant or discordant with the final histological diagnosis
Surgical specimen’s resection planes	Common bile duct, segmental branches, portal vein and hepatic artery, liver parenchyma, periductal dissection margin
Residual disease based on resection margins	Positive frozen section, positive resection plane in the surgical specimen, or a resection plane with a margin of < 1 mm