Fig. 1: Pathological features of mature ovarian teratoma, struma ovarii, complete hydatidiform mole, and mediastinal mature teratoma.

(a) Mature ovarian teratoma is a grossly cystic tumor with hairs and sebaceous material. On histology, skin with pilosebaceous units, cartilage, smooth muscle, and respiratory epithelium are identified (corresponding to case 7 of Fig. 2). (b) In struma ovarii, the gross section shows a brownish nodular area, associated with a cystic area. Histologically, the nodular area resembles a thyroid adenoma with mixed normofollicular and microfollicular pattern (corresponding to case 2 of Fig. 2). (c) In complete hydatidiform mole, molar tissue has a grossly “bunch of grapes” appearance, filling the uterine cavity. Histologically, hydropic villi with central acellular cisternae, trophoblastic inclusions, and circumferential trophoblastic proliferation are evident (corresponding to case 10 of Fig. 2). (d) Mediastinal mature teratoma shows a cystic and solid cut surface. On histology, various tissues, including pancreatic tissue, intestinal mucosa, smooth muscle, and nerve tissue (arrowhead), are identified (corresponding to case 2 of Fig. 2).