Less common pathological conditions

Mucocele of the appendix

Mucocele of the appendix may occur when the proximal end of the lumen slowly becomes completely occluded, usually by a fibrous stricture, and the pent up secretion remains sterile. The appendix is greatly enlarged and sometimes it contains several millilitres of mucus (Fig. 59.9). The symptoms produced are those of mild subacute appendicitis unless infection supervenes, when the mucocele is converted into an empyema. Rupture of a mucocele of the appendix is a cause of pseudomyxoma peritonei. Occasionally, the mucocele is caused by a mucus secreting adenocarcinoma, in which case a right hemicolectomy is the correct treatment.

Diverticulae of the appendix

Diverticulosis of the appendix is relatively rare and the diverticulae may be true congenital (all coats) or acquired (no muscularis layer). The condition may occur in conjunction with mucocele, in which case the intramural pressure rises sufficiently to cause herniation of the mucous membrane through the muscle coat at several points. More often, there is no demonstrable obstruction to the lumen. The patient usually gives a history of previous recurrent attacks of appendicitis. If encountered during the course of an operation for another condition, a diverticulae­bearing appendix should be removed because of a propensity to perforate if inflamed.

Intussusception of the appendix

This is rare and occurs mostly in childhood. It can he diagnosed only at operation. The symptoms usually are not acute. Untreated, the condition may pass on to an appendiculocolic intussusception. The appendix may slough, and this accounts for most of the very rare cases in which the appendix is absent. The treatment is appendicectomy.

Neoplasms of the appendix

Carcinoid tumour (syn. argentaffinoma)

Carcinoid tumours arise in argentaffin tissue (Kulschitzsky cells of the crypts of Lieberkuhn) and are most commonly found in the vermiform appendix. Carcinoid tumour is found once in every 300—400 appendices subjected to histological examination and is 10 times more common than any other neoplasm of the appendix. In many instances the appendix had been removed because of symptoms of subacute or recurrent appendicitis. The tumour can occur in any part of the appendix, but it frequently does so in the distal third. The neoplasm feels moderately hard, and on sectioning the appendix it can be seen as a yellow tumour between the intact mucosa and the peritoneum. Microscopically, the tumour cells are small, arranged in small nests within the muscle and have a characteristic pattern using immunohistochemical stain for Chromogranin B (Fig. 59.21). Unlike carcinoid tumours arising in other parts of the intestinal tract, carcinoid tumour of the appendix rarely gives rise to metastases. Appendicectomy has been shown to be sufficient treatment, unless the caecal wall is involved, the tumour is 2 cm or more in size, or involved lymph nodes are found, otherwise right hemicolectomy is indicated.

Primary adenocarcinoma

Primary adenocarcinoma of the appendix is extremely rare. It is usually of the colonic type and should be treated by right hemicolectomy (as a second-stage procedure if the condition is not recognised at the first operation).