endocrine and metabolic disorders
Carcinoid Syndrome
Etiology of Carcinoid Syndrome
Endocrinologically active tumors of the diffuse peripheral endocrine or paracrine system (neuroendocrine tumors) produce various amines and polypeptides with corresponding symptoms and signs, including carcinoid syndrome. Carcinoid syndrome is usually due to endocrinologically active malignant tumors that develop from neuroendocrine cells (mostly in the ileum—see Small-Bowel Tumors ) and produce An intestinal carcinoid does not usually cause carcinoid syndrome unless hepatic metastases have occurred because metabolic products released by the tumor are rapidly destroyed by blood and liver enzymes in the portal circulation (eg,serotoninby hepatic monoamine oxidase). Hepatic metastases, however, release metabolic products via the hepatic veins directly into the systemic circulation. Metabolic products released by primary pulmonary and ovarian carcinoids bypass the portal route and may similarly induce symptoms. Rare intestinal carcinoids with only intra-abdominal spread can drain directly into the systemic circulation or the lymphatics and cause symptoms. 