This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Anatomy
According to Bismuth classification, type IV Cholangiocarcinoma involves 
Select and explain. 
A. Common hepatic duct, B. Bifurcation only, C. Bifurcation and bilateral secondary intrahepatic ducts, D. Bifurcation and unilateral secondary intrahepatic ducts
C: Bifurcation and bilateral secondary intrahepatic ducts
Answer: C: Bifurcation and bilateral secondary intrahepatic ducts 
Explanation: Bismuth - corlette classification of Hilar Cholangiocarcinoma Type I- Tumor confined to hepatic duct, not involving the main biliary confluence Type II- Tumor involving the main biliary confluence but not extending to the right or left ducts Type IIIa- Tumor extending upto the right secondary biliary confluence Type IIIb- Tumor extending upto the left secondary biliary confluence Type IV - Tumor extending bilaterally to the secondary biliary confluence Ref : Sabiston 20th edition Pgno :1514-1518