Other Pathology

Carcinoid syndrome rarely occurs due to the scarcity of appendiceal carcinoid tumours metastatic to the liver.

Mucocoele

Mucocoeles of obstructed or non-obstructed types both result in marked distension of the lumen by abundant mucus. Obstructed mucocoele is usually <1-2 cm diameter and effectively a retention cyst lined by variably attenuated, atrophic mucosa. The commoner non-obstructed mucocoeles are generally >1-2 cm diameter and due to an abnormality of the underlying mucosa caused either by hyperplastic change (diffuse or polyp), mucinous cystadenoma or mucinous adenocarcinoma. The latter two lesions comprise the group of appendiceal mucinous neoplasms which can be either low-grade (LAMN: mucinous cystadenoma) or high-grade (MACA: mucinous adenocarcinoma) and are of particular relevance to formation of pseudomyxoma peritonei and ovarian muci-nous cystic tumours. LAMNs often have a bland attenuated epithelial lining, which can be confined to the mucosa or dissect through the appen-diceal wall.

Pseudomyxoma peritonei

Mucocoeles can be associated with perforation or mucin dissection resulting in pseudomyxoma peritonei which is either localized or diffuse. Obstructed mucocoeles and those due to hyperplastic change and mucosa-confined adenoma usually remain localized, whereas diffuse pseudomyxoma is due to spillage of either atypical or unequivocally malignant epithelium associated with a LAMN or appendiceal adeno-carcinoma, respectively. Prognosis relates to the extent of extra-appendiceal mucus and the cellularity and atypia of the neoplastic cells within it. However, generalized abdominopelvic disease can result even when the epithelial component is cytologically bland and relatively scanty. Diffuse pseudomyxoma may be helped by debulking procedures but is largely refractory to treatment, slowly but relentlessly progressive and causes death by bowel obstruction (45% 10-year survival). In this condition there is also a strong association with intestinal-type mucinous tumours of the ovary of borderline malignancy which are now regarded as being an implantation deposit from the appendix. Comparative immunophenotyping can help determine the relationship between the tumours. In this respect it should be noted that up to 5% of appendiceal mucinous adenocarcinomas express CK7 as well as the usual CK20. Ovarian mucinous tumours are also CK7/CK20 positive, indicating either an ovarian primary or possible spread from appendix. If CK20 positive alone it is most likely a deposit from an appendiceal or other colorectal lesion. Ovarian tumours of mucinous type can show a wide spectrum of intestinal differentiation and it may be that a significant number of these represent deposits from appendiceal, colonic, gastric or pancreatic sites. In addition, the appendiceal lesion may not be grossly evident and it is recommended that appendicectomy be carried out, particularly if the ovarian tumours are bilateral and mucinous peritoneal disease is present. Occasionally pseudomyxoma peritonei may be due to mucinous carcinomas from other sites, e.g. stomach, colorectal, gall bladder, breast or lung.

Synchronous/metachronous colorectal lesions.

The presence of hyperplastic, adenomatous or cystadenocarcinoma-tous epithelium in the appendix is a marker of concurrent or subsequent epithelial neoplasms elsewhere in the colorectum.

Appendicitis can form an inflammatory appendix mass in the right iliac fossa that mimics colorectal cancer clinically and radiologically. Appen-diceal tumours may also present in this fashion.

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