A 71-year-old male presents with complaints of pruritus, dark urine, and abdominal pain. Physical examination shows jaundice. Laboratory tests include a total bilirubin of 6.3 mg/dL, alkaline phosphatase 4 times the upper limit of normal, and mild elevations in serum transaminases. Ultrasonography shows dilated extrahepatic and intrahepatic bile ducts but no gallstones. There is a 3 cm mass in the head of the pancreas, presumed pancreatic cancer. Which CT finding would indicate that the cancer is not resectable?