Morphological and Immunohistochemical Support for the Origin of the Carcinoid Component in Strumal Carcinoids: A Case Report and Literature Review

Abstract

Strumal carcinoid tumors of the ovary are rare neoplasms composed of an intimate mixture of thyroid and carcinoid tissues. Although various theories regarding their histogenesis have been proposed, evidence confirming the origin of the carcinoid component has been lacking. We report a case of a 40-year-old female with an ovarian strumal carcinoid arising in the background of a mature cystic teratoma. Morphological and immunohistochemical findings support the hypothesis that the carcinoid component originates from the thyroid follicular epithelium, undergoing neuroendocrine differentiation. A single-cell growth pattern was also identified, expanding the known histological spectrum of strumal carcinoids. Our case provides additional immunohistochemical support for the histogenetic origin of strumal carcinoids, offering new insights into their pathogenesis. Recognizing these distinct patterns of staining and unusual morphology is critical for accurate diagnosis and differentiation from metastatic disease.

Keywords: CD56; PAX-8; TTF-1; ovary; single cell pattern; strumal carcinoid; strumal ovarii; synaptophysin; thyroid.

Figure 1

Abdominopelvic magnetic resonance imaging (MRI) shows an adnexal mass, with enhancement.

Figure 2

Histopathological patterns of the carcinoid tumor (HE, 200×). (A) Insular pattern displaying large nests and acini embedded within fibrous stroma; (B) Mixed trabecular and insular pattern with interweaving trabeculae and large nests of tumor cells; (C) Focal mucinous pattern with tumor cells demonstrating intracellular and extracellular mucin accumulation; (D) Isolated single-cell growth pattern observed at the ovarian surface, away from the primary tumor mass; (E) Immunohistochemistry staining positive for synaptophysin in single-cell growth pattern.

Figure 3

Strumal carcinoid arising from struma ovarii. (A) H&E, 100×; immunohistochemistry staining (100×). (B) Strong nuclear TTF-1 expression and (C) strong PAX8 expression in the strumal component, with gradual loss of TTF-1 and retained or weak PAX8 expression observed in the transition into the carcinoid component. (D) Synaptophysin is strongly positive in the carcinoid component, with few scattered positive cells in the strumal component. (E) CD56 shows membranous staining in the thyroid follicular epithelium of the struma and both basal and cytoplasmic expression in the carcinoid tumor cells.