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Thread: Rectal Carcinoid Pictures - Atlas of Colon and Ileum

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    Default Rectal Carcinoid Pictures - Atlas of Colon and Ileum

    Epidemiology
    The age-adjusted incidence of carcinoid tumors worldwide is approximately 2 per 100,000 persons.The average age at diagnosis is 61.4 years.Carcinoid tumors represent about 0.5% of all newly diagnosed malignancies.

    Anatomy
    Carcinoid tumors are rare, slow-growing tumors that originate in cells of the diffuse neuroendocrine system. They occur most frequently in tissues derived from the embryonic gut. Foregut tumors, which account for up to 25% of cases, arise in the lung, thymus, stomach, or proximal duodenum. Midgut tumors, which account for up to 50% of cases, arise in the small intestine, appendix, or proximal colon. Hindgut tumors, which account for approximately 15% of cases, arise in the distal colon or rectum. Other sites of origin include the gallbladder, kidney, liver, pancreas, ovary, and testis.

    GI carcinoid tumors, especially tumors of the small intestine, are often associated with other cancers. Synchronous or metachronous cancers occur in approximately 29% of patients with small intestinal carcinoids. However, it is possible that the association may be due in part to the serendipitous discovery of slow-growing carcinoid tumors, which are found while staging or investigating symptoms from other tumors.

    Histology
    The term carcinoid should be used for well-differentiated neuroendocrine tumors (NETs) or carcinomas of the GI tract only; the term should not be used to describe pancreatic NETs or islet cell tumors. (Refer to the PDQ summary on Pancreatic Neuroendocrine Tumors (Islet Cell Tumors) for more information.) Data regarding carcinoids and other NETs, such as poorly differentiated neuroendocrine carcinomas, may be combined in some epidemiologic and clinical studies, rendering separate consideration difficult. Occurring nonrandomly throughout the GI tract are more than 14 cell types, which produce different hormones.(Refer to the Cellular and Pathologic Classification of Gastrointestinal Carcinoid Tumors section of this summary for more information.) Although the cellular origin of NETs of the GI tract is uncertain, consistent expression of cytokeratins in NETs and the expression of the caudal-related homeodomain protein 2 (CdX2 protein), an intestinal transcription factor in endocrine tumors of the small intestine, suggests an origin from an epithelial precursor cell.
    Rectal Carcinoid Pictures Atlas Colon attachment.php?s=6e81aae9c977dafb1de178513b824871&attachmentid=2055&d=1442181239

    Most NETs of the small and large intestines occur sporadically, while others may occur within the background of an inherited neoplasia syndrome such as multiple endocrine neoplasia type 1 (MEN1) or neurofibromatosis type 1 (NF1) (e.g., gastrin-producing G-cell tumors and somatostatin-producing D-cell tumors of the duodenum, respectively). Tumor multifocality is the rule within the background of neuroendocrine cell hyperplasia, but multifocality is found in approximately one-third of patients with small enterochromaffin cell tumors in the absence of proliferative or genetic factors; clonality studies suggest that most of these neoplasms are separate primary lesions.Gastric carcinoids may be associated with chronic atrophic gastritis.

    Histopathology
    Individual carcinoid tumors have specific histologic and immunohistochemical features based on their anatomic location and endocrine cell type. However, all carcinoids share common pathologic features that characterize them as well-differentiated NETs.In the gastric or intestinal wall, carcinoids may occur as firm white, yellow, or gray nodules and may be intramural masses or may protrude into the lumen as polypoid nodules; the overlying gastric or intestinal mucosa may be intact or have focal ulceration.

    Neuroendocrine cells have uniform nuclei and abundant granular or faintly staining (clear) cytoplasm, and are present as solid or small trabecular clusters, or are dispersed among other cells, which may make them difficult to recognize in sections stained with hematoxylin and eosin; immunostaining enables their exact identification.At the ultrastructural level, neuroendocrine cells contain cytoplasmic membrane-bound dense-cored secretory granules (diameter >80 nm) and may also contain small clear vesicles (diameter 40–80 nm) that correspond to the synaptic vesicles of neurons.

    Molecular genetics
    Occasionally, GI carcinoids occur in association with inherited syndromes, such as MEN1 and NF1.

    MEN1 is caused by alterations of the MEN1 gene located at chromosomal region 11q13. (Refer to the PDQ summary on Genetics of Endocrine and Neuroendocrine Neoplasias for more information.) Most carcinoids associated with MEN1 appear to be of foregut origin. NF1 is an autosomal dominant genetic disorder caused by alteration of the NF1 gene at chromosome 17q11.Carcinoids in patients with NF1 appear to arise primarily in the periampullary region.
    Rectal Carcinoid Pictures Atlas Colon attachment.php?s=6e81aae9c977dafb1de178513b824871&attachmentid=2056&d=1442181250

    In sporadic GI carcinoids, numerous chromosomal imbalances have been found by comparative genome hybridization analysis. Gains involving chromosomes (especially 17q), and 19 and losses involving chromosomes 11 (especially 11q) and 18 appear to be the most common.

    The most frequently reported mutated gene in GI carcinoids is β-catenin (CTNNB1). In one study, β-catenin exon 3 mutations were found in 27 (37.5%) of 72 cases.

    However, no consistent genetic markers for GI carcinoid prognosis have yet been identified. (Refer to the Cellular and Pathologic Classification of Gastrointestinal Carcinoid Tumors section of this summary for more information.)

    Carcinoid syndrome
    Carcinoid syndrome, which occurs in fewer than 20% of patients with carcinoid tumors, is caused by the release of metabolically undergraded vasoactive amines into the systemic circulation. It is associated with flushing, abdominal pain and diarrhea, bronchoconstriction, and carcinoid heart disease.Because vasoactive amines are efficiently metabolized by the liver, carcinoid syndrome rarely occurs in the absence of hepatic metastases. Exceptions include circumstances in which venous blood draining from a tumor enters directly into the systemic circulation (e.g., primary pulmonary or ovarian carcinoids, pelvic or retroperitoneal involvement by metastatic or locally invasive small bowel carcinoids, or extensive bone metastases).

    Site-Specific Clinical Features
    The clinical features of GI carcinoids vary according to anatomical location and cell type. Most carcinoids in the GI tract are located within 3 feet (~90 cm) of the ileocecal valve, with 50% found in the appendix.They are often detected fortuitously during surgery for another GI disorder or during emergency surgery for appendicitis, GI bleeding, or perforation.

    Gastric carcinoids
    Most gastric carcinoids are enterochromaffin-like (ECL)-cell carcinoids; rarely, other types may occur in the stomach. (Refer to Table 1 in the Cellular and Pathologic Classification of Gastrointestinal Carcinoid Tumors section of this summary for more information.)
    Rectal Carcinoid Pictures Atlas Colon attachment.php?s=6e81aae9c977dafb1de178513b824871&attachmentid=2057&d=1442181260

    Type I ECL-cell gastric carcinoids, the most common type, typically do not have clinical symptoms. They are often discovered during endoscopy for reflux, anemia, or other reasons; and are typically multifocal. Occurring most commonly in women (female-to-male ratio, 2.5:1) at a mean age of 63 years, achlorhydria may be present, and hypergastrinemia or evidence of antral G-cell hyperplasia is usually foundThese tumors are gastrin-driven and arise in a background of chronic atrophic gastritis of the corpus, usually because of autoimmune pernicious anemia but sometimes caused by Helicobacter pylori infection.

    Type II ECL-cell carcinoids, the least common type of gastric carcinoids, occur at a mean age of 50 years with no gender predilection. The hypergastrinemia associated with MEN1-Zollinger-Ellison syndrome (ZES) is thought to promote the ECL-cell hyperplasia that leads to type II tumors

    Type I and type II ECL-cell gastric carcinoids have been reported to metastasize in fewer than 10% of cases. Type III gastric ECL-cell carcinoids, the second most common type of gastric carcinoid, occur mostly in men (male-to-female ratio, 2.8:1) at a mean age of 55 years. There are no neuroendocrine manifestations, and patients typically present with signs and symptoms related to an aggressive tumor.

    References:
    Gastrointestinal Carcinoid Tumors - National Cancer Institute











    Last edited by Medical Photos; 09-13-2015 at 09:54 PM.

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