A, Gross photograph of surgical specimen showing a yellow, solid, gelatinous mass. B, Frozen section of the mass from A, showing absence of colloid material in the follicles of struma ovarii during tissue processing. C, Histologic section of the same neoplasm as shown in B, showing both struma ovarii (right) and follicular variant papillary carcinoma (left) components. D, Histologic section of the same neoplasm as shown in C, showing follicular variant papillary carcinoma arising in struma ovarii. Nuclei are enlarged, crowded, and have a ground-glass appearance. Mitosis is absent. E, Histologic section of strumal carcinoid showing the combination of trabecular carcinoid (right) and colloid-containing follicles (left) of struma ovarii. F, Immunohistochemical staining showing immunoreactivity of strumal (left) and carcinoid (right) components for thyroglobulin. G, Immunohistochemical staining showing immunoreactivity of strumal (left) and carcinoid (right) components for synaptophysine (right) (hematoxylin-eosin, original magnifications ×200 [B], ×100 [C and E], ×400 [D]; thyroglobulin, original magnification ×100 [F]; synaptophysine, original magnification ×100 [G]).