Carcinoid Syndrome and Neuroendocrine Tumors

Eighty percent of gastrointestinal (GI) neuroendocrine tumors are made up of enterochromaffin-like cell carcinoids, duodenal gastrin G-cell tumors, and rectal trabecular L-cell carcinoids. Less common neuroendocrine tumors are gangliocytic paragangliomas, somatostatinomas, lipomas, and schwannomas. Pathologic study has revealed that the term carcinoid represents a wide spectrum of neoplasms that originate from different neuroendocrine cells.

Carcinoid tumors of the small intestine that secrete serotonin (5-hydroxytryptamine [5-HT]) are associated with the carcinoid syndrome. These neuroendocrine tumors may originate from the foregut, midgut, or hindgut, and the enterochromaffin cells making up the neoplasm may secrete serotonin, gastrin, or adrenocorticotropic hormone. Consequently, they can produce different syndromes. However, the most frequent site for carcinoid tumors is in the GI tract, and the second most common site is the bronchopulmonary system. The most common site within the GI tract is the small bowel, followed by the appendix, with a significant number occurring in the rectum. Neoplasms are usually small and yellowish. Those found in the appendix rarely metastasize, whereas those originating in the small bowel can be more virulent. They can develop anywhere in the GI tract and have been reported in the esophagus, stomach, pancreas, and large bowel.

Carcinoid syndrome occurs when the tumor secretes a large amount of an active substance such as serotonin. Symptoms occur from the carcinoid when the tumors grow larger or when they metastasize. Carcinoid tumors smaller than 1 cm rarely metastasize. Lesions larger than 2 cm should be treated aggressively.

Rectal carcinoids do not result in the carcinoid syndrome, and most are asymptomatic.

Clinical Picture

Frequently, carcinoids are discovered inadvertently during surgery in the appendix or during a workup. Often, the carcinoids are asymptomatic. In other cases, the carcinoid can cause mild abdominal pain, bleeding, or intussusception, which would then manifest as intermittent abdominal pain or acute obstruction ( Fig. 74.1 ). Rarely, carcinoids manifest as a palpable mass.

When the tumor secretes an active substance, as in approximately 10% of patients, the resulting symptoms are referred to as carcinoid syndrome. The patient typically experiences intermittent abdominal cramps associated with diarrhea, flushing of the face and entire body, and extragastrointestinal symptoms of bronchospasm or even cyanosis.

On physical examination, again rarely or occasionally, a palpable mass heralds the diagnosis. However, most often, there are no findings except when acute intussusception and obstruction occur. In patients with carcinoid syndrome, the physical examination may reveal murmurs of tricuspid valve disease. Carcinoid is associated with fixation of the tricuspid valve leaflets, resulting in typical murmurs. Left-sided heart disease occurs in 10% to 15% of patients. The presentation of the patient with flushing, diarrhea, and tricuspid murmur is classic and almost pathognomonic of the carcinoid syndrome.