While the etiology of most carcinoid tumors is unknown, rare carcinoid tumors of the stomach have been associated with Pernicious Anemia or prolonged therapy with H2 blockers.
Carcinoids arise from neuroendocrine cells of endodermal derivation which are normally present in the stomach.
While gastric carcinoids are rare, they have been associated with Pernicious Anemia and chronic therapy with H2 blockers. These have been associated with a multicentric neuroendocrine hperplasia with formation of "tumourlets" and eventually Carcinoid Tumors.
The presumed mechanism is neuroendocrine cell proliferation stimulated by elevated gastrin levels.
The pathogenesis of the vast majority of Carcinoid Tumors is unknown.,
The peak incidence of carcinoids is the sixth decade.
No other sex, racial or geographic preference.
|General Gross Description|
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 serendipously, 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 are found to have signifcant liver metastases at the time of discovery.
|General Microscopic Description|
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 ultrastructuraly, but these techniques have generaly 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 malignant behavior can not be made on the histologic appearance.
Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th ed. Philadelphia, W.B. Saunders, 1994, pp. 818-820.
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||Synopsis by: Martin Nadel M.D. (T64000M82403)