Ovarian carcinoid. Light micrograph of a primary ovarian carcinoid showing insular architecture consisting of a uniform population of tumour cells arranged in tubular and glandular structures separated by fibrous stroma. Note the prominent retraction artifact around the glandular structures. Ovarian carcinoids can be primary or metastatic. Primary ovarian carcinoid is a germ cell tumour that resembles well-differentiated neuroendocrine tumours arising in the gastrointestinal tract. Most cases occur as a component of mature cystic teratoma and develop from the neuroendocrine cells within intestinal-type or respiratory epithelium of the teratoma. Pure ovarian carcinoids are a form of monodermal teratoma and contain no other teratomatous elements. Primary ovarian carcinoids are rare and comprise less than 0.1% of all ovarian neoplasms. Metastatic ovarian carcinoids originate from the primary tumours located in the gastrointestinal tract, lung, or other sites. Haematoxylin and eosin stained section. Magnification: x200 when printed at 10 centimetres wide.