Embryology of the gonad with reference to special tumors of the ovary and testis.

The ovaries and testes have very similar development patterns until about the fourth month of embryonic life. A review of the similar development (until the fourth month) provides an explanation for the origin of tumors commonly associated with ovarian tissue appearing in the testis and vice versa. Embryonic surface epithelium gives rise to mesothelial tissue from which the common epithelial tumors arise in the ovary. Since these cells disappear from the testis when the tunica albuginea develops, this offers an explanation for the lack of common epithelial tumors in the testis. The embryonic gonadal tissue or sex cord epithelium and the primitive germ cells give rise to similar tumors in both the ovary and the testis. The extraembryonal tumors arise from the extraembryonal cells and trophoblastic cells, which give rise to the endodermal sinus tumors and choriocarcinomas, respectively. Since there is such a similarity in the development of the ovary and testis with the potential for residual cells to remain, an explanation is offered for the development of similar tumors in the ovary and the testis.