Methods: The study population was divided into 4 groups: 12 infants with choledochal cyst, aged 4 m to 12 m, were classified as the infant choledochal cyst (ICC) group; 36 children, aged 1 y to 14 y, were classified as the children with choledochal cyst (CCC) group; while 18 patients, aged 2 m to 5 m, with biliary atresia (BA) were included as positive controls; and 14 infants, aged 1 d to 3 y, who died from non-liver diseases served as negative controls (CON). Liver specimens were examined using H&E sections to score fibrosis by means of Ohkuma's classification, and immunohistochemical sections were evaluated by counting the cells positive for cytokeratin (CK) and human leukocyte antigen-DR (HLA-DR) to discover the pathogenic factors of fibrosis.
Results: Most ICC patients had clinical biliary obstruction. The liver fibrosis score was highest in the BA group (2.9 +/- 0.7). The fibrosis score in the ICC group was higher (2.5 +/- 0.9) than that of the CCC (1.5 +/- 1.2; p < 0.05) and of the CON (0.1 +/- 0.4; p < 0.01) groups. The densities of CK-positive cells were 164 +/- 80/HP, 253 +/- 165/HP, 70 +/- 57/HP and 23 +/- 12/HP in the BA, ICC, CCC and CON groups, respectively, and differed significantly (p < 0.01) with the exception of the ICC vs. the BA group. The densities of HLA-DR positive cells were 130 +/- 72/HP, 98 +/- 54/HP, 96 +/- 50/HP and 36 +/- 13/HP in the portal area in the BA, ICC, CCC and CON groups, respectively. The density was lowest in the CON group (p < 0.01).
Conclusion: In patients with choledochal cyst, liver fibrosis is more common and severe in infants than in children. Obstruction of the bile duct and proliferation of bile duct cells were the main pathogenic factors for fibrosis, while HLA-DR mediating immuno-injury may play a limited role.