Teratomas

Teratomas are divided into three categories: (1) mature (benign), (2) immature (malignant), and (3) monodermal or highly specialized.

Mature (Benign) Teratomas

Most benign teratomas are cystic and are better known in clinical parlance as dermoid cysts. Cystic teratomas are usually found in young women during the active reproductive years.75 They may be discovered incidentally, but are occasionally associated with clinically important paraneoplastic syndromes, such as inflammatory limbic encephalitits, which may remit upon removal of the tumor.

Morphology. Benign teratomas are bilateral in 10% to 15% of cases. Characteristically they are unilocular cysts containing hair and cheesy sebaceous material (Fig. 22-43). On section, they reveal a thin wall lined by an opaque, gray-white, wrinkled epidermis. From this epidermis, hair shafts frequently protrude. Within the wall, it is common to find tooth structures and areas of calcification.

On histologic examination the cyst wall is composed of stratified squamous epithelium with underlying sebaceous glands, hair shafts, and other skin adnexal structures (Fig. 22-44). In most cases structures from other germ layers can be identified, such as cartilage, bone, thyroid tissue, and neural tissues. Dermoid cysts are sometimes incorporated within the wall of a mucinous cystadenoma. About 1% of the dermoids undergo malignant transformation (e.g., thyroid carcinoma, melanoma, but most commonly, squamous cell carcinoma).

In rare instances a benign teratoma is solid and composed entirely of benign-looking heterogeneous collections of tissues and organized structures derived from all three germ layers. These tumors presumably have the same histogenetic origin as dermoid cysts but lack preponderant differentiation into ectodermal derivatives. These neoplasms may be difficult to differentiate, on gross inspection, from the malignant, immature teratomas.

The origin of teratomas has been a matter of fascination for centuries. Some common beliefs blamed witches, nightmares, or adultery with the devil. The karyotype of almost all benign ovarian teratomas is 46,XX. From the results of chromosome banding techniques and the distribution of electrophoretic variants of enzymes in normal and teratoma cells, it has been suggested that the tumors arise from an ovum after the first meiotic division.96 Other derivations have also been proposed.97

Monodermal or Specialized Teratomas

The specialized teratomas are a remarkable, rare group of tumors, the most common of which are struma ovarii and carcinoid. They are always unilateral, although a contralateral teratoma may be present. Struma ovarii is composed entirely of mature thyroid tissue. Interestingly, these thyroidal neoplasms may hyperfunction, causing hyperthyroidism. The ovarian carcinoid, which presumably arises from intestinal epithelium in a teratoma, may also be functional, particularly large (>7 cm) tumors, producing 5-hydroxytryptamine and the carcinoid syndrome. Primary ovarian carcinoid can be distinguished from metastatic intestinal carcinoid, which is virtually always bilateral. Even rarer is the strumal carcinoid, a combination of struma ovarii and carcinoid in the same ovary. Only about 2% of carcinoids metastasize.