The cause of sacrococcygeal teratomas is unknown. Sacrococcygeal teratomas are germ cell tumors. Germ cells are the cells that develop into the embryo and later on become the cells that make up the reproductive system of men and women. Most germ cell tumors occur in the testes or ovaries (gonads) or the lower back. When these tumors occur outside of the gonads, they are known as extragonadal tumors. Researchers do not know how extragonadal germ cell tumors form. One theory suggests that germ cells accidentally migrate during to unusual locations early during the development of the embryo (embryogenesis). Normally, such misplaced germ cells degenerate and die, but in cases of extragonadal teratomas researchers speculate that these cells continue to undergo mitosis, the process where cells divide and multiply, eventually forming a teratoma. Sacrococcygeal teratomas are thought to arise from an area under the coccyx called "Henson's Node". This is an area where primitive cells persist (germ cells) that can give rise to cells of the three major tissue layers of an embryo: ectoderm, endoderm, and mesoderm. These embryonic layers eventually give rise to the various cells and structures of the body. Sacrococcygeal teratomas can contain mature tissue that looks like any tissue in the body, or immature tissue resembling embryonic tissues. Ref-