Fig. 9.19 Biliary papillomatosis. A Large, thickened intrahepatic and extrahepatic bile ducts. B Villous pattern. C There is no invasion by tumour cells.

els. The neoplastic columnar cells extend into the epithelial invaginations and the antral-type glands. Formation of cribriform structures in the lamina propria occurs. This tumour also has scattered endocrine cells, most of which are immunoreactive for serotonin. Two examples of in situ signet-ring cell carcinoma confined to the surface epithelium and to the epithelial invaginations of the gallbladder have been reported {40}. These in situ signet ring cell carcinomas represented incidental findings in cholecystectomy specimens and were cytologically similar to those reported in the stomach. This unusual form of carcinoma in situ should be distinguished from epithelial cells which acquire signet-ring cell morphology when desquamated within the lumen of dilated metaplastic pyloric glands in cases of chronic cholecystitis and from mucin-containing histiocytes (muci-phages).

The morphological type of in situ carcinoma does not always correspond with that of the invasive carcinoma. For example, we have seen conventional adeno-carcinoma in situ in the mucosa adjacent to invasive squamous, small cell, and undifferentiated carcinomas. The wall of the gallbladder with dysplasia or carcinoma in situ usually shows variable inflammatory changes, typically with a predominance of lymphocytes and plasma cells, although lymphoid follicles with germinal centers, xanthogranuloma-tous inflammation or an acute inflammatory reaction may be present.

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