Pathology

Macroscopically:

• consists of a yellowish plaque with intact overlying mucous membrane. This later ulcerates.
• at the time of the diagnosis the tumour is usually the encircling the bowel. This may cause obstruction.

Microscopically:

• composed of Kultchitsky cells; these arise in the crypts of the intestinal mucosa; they take up silver-stains.

Carcinoid tumours are very slow growing. Those tumours arising in the appendix are relatively benign but approximately 3% eventually metastasise. Carcinoid tumours of the large bowel and ileum spread to the regional lymph nodes and the liver.

The carcinoid syndrome is the result of the serotonin (5HT) secreted by the carcinoid cells. The features of the carcinoid syndrome are only present when sufficient 5HT escapes hepatic degradation.