Carcinoid tumors develop from neuroendocrine cells in the gastrointestinal tract (90%), pancreas, pulmonary bronchi, and rarely the genitourinary tract. More than 95% of all gastrointestinal carcinoids originate in only 3 sites: the appendix, ileum, and rectum.
Although carcinoids are often benign or only locally invasive, those affecting the ileum and bronchus are frequently malignant. Malignant tumors range between well differentiated and poorly differentiated, with corresponding variability in aggressiveness. They typically spread to the liver and/or regional lymph nodes, although other metastatic sites are possible.
Carcinoids can be
Endocrinologically inert
Endocrinologically active (produce hormones)
The most common endocrinologic syndrome arising from carcinoid tumors is carcinoid syndrome; however, most patients with carcinoid tumors do not develop carcinoid syndrome. The likelihood that a tumor will be endocrinologically active varies with its site of origin, being highest for tumors originating in the ileum and proximal colon (40 to 50%). The likelihood is lower with bronchial carcinoids, lower still with appendiceal carcinoids, and essentially zero with rectal carcinoids.
Endocrinologically inert carcinoids are suspected because of their symptoms and signs (eg, pain, luminal bleeding, gastrointestinal obstruction). They can be detected by angiography, CT, or MRI. Small-bowel carcinoids may exhibit filling defects or other abnormalities on barium x-rays. Definitive diagnosis and grading are determined histologically after biopsy or resection.
Staging evaluation typically includes imaging with MRI (probably preferred over CT scan) and sometimes imaging with somatostatin receptor-based imaging techniques, which can be useful in detecting endocrinologically inert tumors as well.
Treatment of nonmetastatic carcinoid tumors is usually surgical resection. The type of surgery depends on the location and the size of the tumor.
Endocrinologically active carcinoids are diagnosed and treated as described for carcinoid syndrome.
