Net of the appendix and ileum E34.0

Epithelial tumor, starting from enterochromaffin cells (EC cells) of the diffuse neuroendocrine system (DENS), which are characterized by the production of tissue hormones and enzymes such as serotonin, kallikrein, tachykinin, prostaglandins, etc.

Nets-Ileum: Frequently multiple neuroendocrine tumors which occur mainly in the terminal ileum and occasionally also in the immediately adjacent cecum with involvement of the ileocecal valve.

1/100,000 persons per year; the NET of the appendix and the ileum are among the most frequent GEP-NET.

Frequency peaks between 40 and 70 years of age (exception: NET appendices: not seldom in younger persons as a random finding in 0.3% of appendectomies).

Occurrence in the appendix 3x more frequently than in the jejunum

Prognosis of the NET appendix much more favourable than the NET ileum. This is remarkable as the Net-Appendix without exception infiltrates the Muscularis propria and also the adjacent fat tissue of the Mesoappendix. Regional lymph node metastases are rare (only with tumor size from 2.5 cm). Most NET-Appendix can be treated curatively by an appendectomy. Rare are hormone hypersecretion syndromes starting from a NET-Appendix.

The NETs-Ileum are diagnosed very late, because they are initially completely asymptomatic. At the time of diagnosis they are usually > 2 cm and infiltrate the muscularis propria. Thus lymph node metastases and liver metastases are to be expected in about 20% of patients.

The very rare goblet cell carcinoids, mixed exocrine endocrine tumours, must be distinguished from the classic appendix NETs, as they are less favourable in prognosis.

If a carcinoid syndrome develops (flush, diarrhoea and endocardial fibrosis), liver metastases are present because serotonin first reaches the liver via the portal circulation and is broken down there. Only in the case of liver metastases can serotonin enter the large circulation in a clinically relevant and active way.