Histological evaluation of intracapsular venous invasion for discrimination between portal and hepatic venous invasion in hepatocellular carcinoma

Background and Aim: Histological criteria for intracapsular venous invasion (IVI) that would allow its discrimination between portal and hepatic venous invasion in hepatocellular carcinoma (HCC) have not been established. Methods: We evaluated IVI immunohistochemically to discriminate between portal and hepatic venous invasion in 89 resected specimens from patients with HCC. IVI was defined as the microscopic involvement of the vessels within the fibrous capsule of HCC. The hepatic venous system was subdivided into the central vein and the sublobular/hepatic vein. Immunohistochemical analysis with the D2-40 monoclonal antibody revealed lymphatic vessels. Results: In non-neoplastic liver tissues, the portal veins (n = 4355) were accompanied by lymphatic vessels (99.7%), bile ductules (100%) and arteries (96%), whereas the central veins (n = 3932) and sublobular/hepatic veins (n = 662) were rarely accompanied by lymphatic vessels (0% and 17%, respectively) and bile ductules (12% and 33%, respectively). In total, 29 IVI foci were detected; three foci were clearly visible within vessels that contained a distinct layer of connective tissue fibers, signifying sublobular/hepatic venous invasion. As the remaining 26 foci were accompanied by lymphatic vessels (26/26 [100%]), bile ductules (21/26 [81%]) and arteries (10/26 [38%]), these foci were considered to reflect intracapsular portal venous invasion rather than venous invasion of the central vein. Intracapsular portal venous invasion was significantly associated with extratumoral portal venous invasion (P < 0.001). Conclusions: D2-40 immunoreactivity for the histological evaluation of IVI in HCC allows discrimination between portal and hepatic venous invasion for cases in which portal venous invasion predominates.