The macroscopic pathology of small bowel carcinomas is determined by a number of factors, of which stage and site are the most significant. Many carcinomas of the jejunum and ileum are detected at an advanced stage {498, 189}. A further determinant of the macroscopic features is the presence or absence of predispos

Fig. 4.01 A Tubulovillous adenoma of the duodenum and the ampulla of Vater which is greatly distended. B Villous adenoma of duodenum adjacent to normal mucosa.

ing factors, namely, an associated adenoma, coeliac disease, Crohn's disease, radiotherapy, previous surgery (notably pouch surgery and ileostomy), polyposis syndromes, Meckel's diverticulum, and intestinal duplication. Carcinomas may be polypoid, infiltrating or stenosing. Jejunal and ileal carcinomas are usually relatively large, annular, constricting tumours with circumferential involvement of the wall of the intestine {189}. Most have fully penetrated the muscularis propria and there is often involvement of the serosal surface {16}. Adenocarcinoma of the ileum may mimic Crohn's disease clinically, radiologically, endoscopically, and at macroscopic pathological assessment {745}. Although circumferential involvement can occur, duodenal carcinomas are usually more circumscribed, with a macroscopically demonstrable adeno-matous component in 80% of cases {966, 496}. Thus, they are often protuberant or polypoid, and the central carcinomatous component may show ulceration {1267}. Carcinomas arising at the ampulla of Vater tend to cause obstructive jaundice before they have reached a large size; they are usually circumscribed nodules measuring not more

Fig. 4.02 Adenocarcinoma of small intestine.

than 2-3 cm in diameter. They may be within the wall of the duodenum or project into the lumen as a nodule. Unusual macroscopic features, e.g., the lack of ulceration, the predominance of an extramural component and the presence of multicentricity, should alert the pathologist to the possibility that the tumour is a metastasis.

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