Fig. 5.02 Appendiceal mucinous adenocarcinoma.

Fig. 5.03 Pseudomyxoma peritonei. A Several loops of bowel are encased in a multilocular mucinous mass. B Well differentiated mucus producing epithelium embedded in a fibrous matrix; mucus is present within the lumen and is extravasated into the stroma.

diagnosis in itself; the prognosis will depend on the nature of the causative lesion. Nevertheless, pseudomyxoma peritonei is often applied to a distinctive clinical picture produced by well differentiated mucinous adenocarcinomas in which the growth of malignant cells within the peritoneal cavity causes a slow but relentless accumulation of mucin. Cells may be very scanty within this mucinous material.

A distinctive feature of well differentiated mucinous carcinomatosis is its distribution in the abdomen. There is a tendency to spare the peritoneal surfaces of the bowel, whereas large-volume disease is found in the greater omentum, beneath the right hemidiaphragm, in the right retrohepatic space, at the ligament of Treitz, in the left abdominal gutter and in the pelvis {1854}. In these cases, tumour growth tends to remain confined to the abdomen for many years. Mucinous cysts within the spleen occur occasionally {433}.

It has been suggested that appendiceal adenomas can cause widespread pseu-domyxoma peritonei with an ultimately fatal outcome, and some authors use the term 'adenomucinosis' for the spread of such lesions through the abdomen {1611, 1612}. It is considered more likely that

Fig. 5.04 Pseudomyxoma peritonei.

such cases are examples of well differentiated adenocarcinoma. Although most cases of pseudomyxoma peritonei are due to spread from a primary carcinoma of the appendix, cases have been reported in association with mucinous carcinomas of other sites, including gallbladder, stomach, colorec-tum, pancreas, fallopian tube, urachus, lung, and breast {346, 612, 707, 981, 1199, 2199}.

Although the ovary has been thought of as a common primary site {104, 1705}, there is an accumulating body of evidence based on immunohistochemistry and molecular genetics suggesting that this is not the case, and that in most patients with low-grade mucinous tumours of the ovary and appendix with pseudomyxoma peritonei the lesions are probably metastatic from an appendiceal primary {1536, 1611, 1612, 1871, 2187}.

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