• This carcinoid tumor is fairly large for this type of tumor

• Note that the mucosa has remained intact in spite of the size of the tumor

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•The etiology of intestinal carcinoid tumors is unknown.

•Carcinoid tumors arise from neuroendocrine cells of gut mucosa, but it uncertain whether differentiated or immature neuroendocrine cells are the origin.

•Carcinoids arise from Neuroendocrine cells of endodermal derivation.

•The pathogenesis of intestinal carcinoids is unknown.

•While the vast majority of carcinoids arise in the GI tract, they can be found wherever endodermal derived tissue is seen, such as teratomas most commonly in the Ovary,

•The peak incidence of carcinoids is the sixth decade.

•No other sex, racial or geographic preference has been described.

•Carcinoids are slow growing low grade malignant tumors

•Appendiceal and rectal carcinoids virtually never metastasize.

•Most carcinoids that do metastasize originate in the ileum, usually the distal ileum.

•The most common symptom is non-specific abdominal pain, which has usually been present for a number of years. Bleeding is rare, and obstruction can occur due to size of the tumor, desmoplastic thickening of the intestinal wall, intestinal infarction secondary to mesenteric vessel compression by tumor, or intussusception.

•Metastases first occur in regional nodes and then the liver.

•When first diagnosed, only 25% of patients with Ileal carcinoids will have disease limited to the intestine, and 25% will already have liver metastases.

•The most striking presentation of these tumors is the Carcinoid Syndrome. Less than 1% of carcinoid tumors will demonstrate this, and almost all are primary in the Ileum.

•The presence of the Carcinoid Syndrome indicates release of polypeptide hormones or vasoactive amines into the general circulation and in most cases denotes bulky hepatic metastases.

•The two most common symptoms of the Carcinoid Syndrome are flushing and diarrhea, and these are almost always associated with an elevated 5-HIAA, although the amines responsible for the symptoms are not clearly identified.

•Carcinoid tumors in other locations may secrete a variety of hormone products such as Gastrin, Insulin, ACTH, Somatostatin, VIP, etc.

•For additional information about prognosis and treatment, consult the NCI web site.

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•While carcinoids are found the entire length of the GI tract, 95% arise in the Appendix, Ileum and Rectum.

•These tumors are fairly well circumscribed but not encapsulated, white or pale yellow tan, and very firm due to a marked desmoplastic reaction.

•When found serendipitously, 75-80% of Appendiceal and Rectal Carcinoids are less than 1cm, while over half of Ileal Carcinoids are over 1.5cm.

•The overlying mucosa is usually intact, and the tumor is seen as a submucosal smooth nodule.

•Large lesions can ulcerate the mucosa or penetrate the serosa.

•Virtually all symptomatic carcinoids have metastasized when diagnosed, and these lesions gnerally over 2cm in size.

•The nomenclature of Carcinoid tumors is in flux, with some restricting the term to those tumors showing the classical histologic patterns described for Carcinoids, while other prefer to use the term neuroendocrine tumor for all tumors showing a predominant neuroendocrine expressiopn.

•While carcinoid tumors have many different histologic appearances, the main patterns are: solid, often with peripheral palisading; trabecular, forming ribbon-like strands; acinar or gland-like; and insular, cribiform arrangement similar to islets.

•Individual tumor cells have well defined cell borders, centrally placed small nuclei with a finely stippled chromatin pattern, small or abscent nucleoli and moderate amount of cytoplasm varying from acidophilic to basophilic,

•The most striking feature is the bland monotous uniform appearance of the tumor without pleomorphism or mitotic activity.

•Confirmation of the neuroendocrine nature of Carcinoid tumors was their positive argyrophilic (silver) staining, with the Grimelius Stain being the most usefull.

•The argyrophilic positive neurosecretory granules can also be demonstrated ultrastructurally, but these techniques have generally been replaced by immunoperoxidase identification of the neurosecretory granules using either a general marker such as chromogranin, or specific hormone markers such as gastrin, somatostatin, or serotonin,.

•As with other endocrine tumors, prediction of aggressive biologic behavior is not possible on histologic grounds with the only absolute critieria being the presence of metastases.

•Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th ed. Philadelphia, W.B. Saunders, 1994, pp.818-820.

• Current literature from PubMed at National Library of Medicine