Primary ovarian carcinoid arising in associated mature cystic teratoma - BMC Women's Health - BioMed Central

Although ovarian carcinoid (OC) is a well-differentiated neuroendocrine tumor (NET) resembling those arising from the digestive system, there is no established nomenclature for this tumor. According to the 5^th WHO classification [1, 2], we can consider this case as a well-differentiated neuroendocrine tumor, Grade 1 (NET, G1) arising from an mature cystic teratoma, but the ICD-O coding is different between the two systems [1, 7]. From the limited data of primary OC, the prognosis is generally excellent, but relapse, metastasis, or even death had been reported [8,9,10,11,12,13,14]. Fortunately, this woman was surjected to a radical surgery and was in good condition at the current follow-up. Close follow-up, however, will continue for a long time. Therefore, we think it's necessary to develop the current OC classification, and we recommended it would be best to follow the 5^th WHO classification of tumors of the digestive system [1].

Considering clinical manifestations, most patients are perimenopausal or postmenopausal females aged from 14 to 83 years (mean age: 53 years) [8]. Clinical symptoms are usually not specific, and occasionally abdominal pain, vaginal bleeding, and dysmenorrheal were reported [8]. Besides, carcinoid symptoms are seen in some insular carcinoid cases [9]. Owing to the rarity of OC, it's important for pathologists to exclude the possibility of metastatic low-grade NET by combining imaging examinations before we achieve the diagnosis of primary OC. On the other hand, the patients, just like the present woman, undergo radical surgery and have a good outcome for ovary-confined tumor; but, given the malignant potential of the disease, they should continue to be monitored attentively.

Recently, Bidzinski et al. [10] divided OC into 4 categories based on the histopathologic characteristics: insular, strumal, trabecular, and mucinous carcinoid. (1) Insular carcinoid displays solid nests that are often punctuated by peripheral acini [11]. (2) Strumal carcinoid, intimately admixed or juxtaposed with thyroid follicles, is composed of insular or trabecular carcinoid [3]. (3) Trabecular carcinoid displays parallel ribbons, cords, or trabeculae, and the neoplastic cells are uniform and round to oval, containing pink cytoplasm and centrally located nuclei with salt-and-pepper chromatin. (4) Mucinous carcinoid is akin to an appendix carcinoid microscopically. Teratomatous elements in the ipsilateral or contralateral ovary may be present in all types of OC [12, 13]. In our study, this case was a trabecular OC.

Currently, the origin of primary ovarian carcinoid is still unclear. Vora et al. [14] suspected it arose from neural crest. Niu et al. [13] stated that the insular and mucinous types are considered as a midgut derivation, and trabecular and strumal carcinoid represent foregut or hindgut derivations.

In brief, careful morphological observation combined with appropriate ancillary histochemical kits are essential for our pathologists to approach the diagnosis of primary ovarian carcinoid arising from mature cystic teratoma, and long-term follow-up is required for this low grade ovarian neuroendocrine tumor.