Vascular invasion CT scan classification of vascular involvement includes 4 grades according to the tumor / vessel relationship - Grade 0: no tumor-vessel contact - Grade I: vacular involvement ≤ 90o - Grade II: vacular involvement > 90o and ≤180o - Grade III: vacular involvement > 180o 1.4 Outcomes of pancreaticoduodenectomy with standard lymphadenectomy for pancreatic head region cancer 1.4.1.