A case of inflammatory pseudotumour of the common bile duct.

Inflammatory pseudotumour of the common bile duct (CBD) is extremely rare. A 58-year-old Japanese female without choledocolithiasis underwent pancreatico-duodenectomy for constriction of the middle lower region of the CBD. A submucosal tumour protruding into the CBD, was histologically inflammatory consisting of fibroblastic cells, collagen fibres and myxoid stroma with chronic inflammatory cells. This lesion was surrounded by an irregular fibrosclerosing lesion with obliterative phlebitis which involved the neighbouring pancreas and lymph nodes. Clonal analysis of the tumour by polymerase chain reaction analysis of X chromosome inactivation patterns, confirmed the polyclonal nature of the lesion. Immunohistochemically, the fibroblastic cells in both lesions had the same phenotype [vimentin (+), desmin (-), muscle-specific actin (-) and CD34 (+)] suggesting that these lesions with different histological features represent zonation of the same inflammatory process. The outer lesion extended irregularly into adjacent pancreatic tissue and lymph nodes. This fact made it difficult to differentiate this from a malignant lesion, even if frozen sections contained no atypical cells.