A 38-year-old woman comes to the hospital with 4 hours of abdominal pain, nausea, and vomiting. The pain started in the periumbilical area and is now localized to the right lower quadrant. Temperature is 38.3 C (100.9 F). On examination, the patient has right lower quadrant tenderness with guarding. An appendectomy is performed, and light microscopy of the appendix shows transmural neutrophilic inflammation, consistent with the diagnosis of acute appendicitis. Further microscopic evaluation reveals abnormal islands of cells, as shown in the image below.
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This lesion is most likely derived from which of the following?
Histopathology of this patient's appendix shows a well-differentiated neuroendocrine tumor (WDNET) (ie, carcinoid tumor). WDNETs are derived from neuroendocrine cells and often arise in the gastrointestinal tract (eg, small intestine, rectum, appendix).
Microscopically, WDNETs can show a variety of architectural patterns (eg, islands, nests, trabeculae) and are composed of uniform tumor cells with round nuclei, salt and pepper chromatin, and eosinophilic (ie, pink) cytoplasm. The cytoplasm contains dense-core neurosecretory granules seen using electron microscopy, with secretory products such as vasoactive molecules (eg, serotonin) and hormones (eg, gastrin).
WDNETs are the most common appendiceal tumors and are usually incidentally found at the distal tip of the appendix in patients who have undergone appendectomy for unrelated reasons. However, tumors at the base can obstruct the lumen, causing appendicitis. The majority of appendiceal WDNETs follow an indolent clinical course, but larger tumors can metastasize. In rare cases, metastasis to the liver can result in carcinoid syndrome (eg, flushing, diarrhea, bronchospasm).
(Choice A) Endothelial cells can give rise to vascular tumors such as angiosarcoma, which typically involves the skin, breast, or liver. Histopathology often shows infiltrative vascular structures lined by atypical (eg, large, hyperchromatic) endothelial cells.
(Choice B) Desmoid tumor (ie, deep fibromatosis) is a benign but locally invasive fibroblastic tumor that can slowly infiltrate the abdominal cavity, causing nausea and intestinal obstruction. However, histopathology shows long fascicles of uniform, spindle-shaped fibroblasts in a collagen-rich stroma.
(Choice C) Abnormal proliferation of hematopoietic cells can lead to a variety of myeloid and lymphoid neoplasms (eg, Burkitt lymphoma). Although it may involve the appendix and cause abdominal pain, the histopathology of Burkitt lymphoma involves sheets of basophilic lymphoid cells with scattered, benign macrophages (ie, "starry sky" appearance).
(Choice D) Intestinal epithelial cells can give rise to adenocarcinoma. Appendiceal adenocarcinoma can present with symptoms of acute appendicitis, but the histopathology often shows infiltrative glands and/or mucin.
(Choice F) Leiomyomas are benign smooth muscle tumors that typically involve the gynecologic tract (eg, uterine mass). Histopathology shows bundles of uniform cells with spindle-shaped nuclei and pink cytoplasm.
Educational objective:
Well-differentiated neuroendocrine tumors (ie, carcinoid tumors) arise from neuroendocrine cells and are composed of uniform tumor cells with round nuclei, salt and pepper chromatin, and eosinophilic cytoplasm. Although most are found incidentally (ie, asymptomatic), some may obstruct the lumen, causing acute appendicitis.