Fig. 1

Histologic sections of malignant struma ovarii. Areas of adenomatous differentiation (a - lower right) and classic papillary thyroid carcinoma (a - center left) with papillary growth and cleared out “orphan Annie” nuclei. Area of Hurthle cell differentiation (a – center right) with an illustrative mitosis (a – inset). Tumor proliferation impinging on vascular structures (b). While the irregular border of the tumor and myxoid degeneration of the vessel wall are suggestive of infiltrative growth, no definitive vascular invasion is identified in the histologic sections reviewed. Tumor proliferation extends into the ovarian capsule (arrows) without extra-capsular extension (c). Struma ovarii (d - upper left) and squamous differentiation of the mature cystic teratoma (d - mid-lower right). Immunohistochemical stain for thyroid transcription factor (TTF-1) at 40× magnification with positive staining only in the areas of thyroid differentiation (e). a-d are hematoxylin and eosin stained with magnification 200× (a), 100× (b), and 40× (c, d)