A 43-year-old man has experienced progressive fatigue, pruritus, and icterus for 4 months. A colectomy was performed 5 years ago for the treatment of ulcerative colitis. On physical examination, he now has generalized jaundice. The abdomen is not distended; on palpation, there is no abdominal pain and there are no masses. Laboratory studies show a serum alkaline phosphatase level of 285 U/L and an elevated titer of anti-neutrophil cytoplasmic antibodies. Cholangiography shows widespread intrahepatic biliary tree obliteration and a beaded appearance in the remaining ducts. Which of the following morphologic features is most likely to be present in his liver?