Sacrococcygeal teratoma in the perinatal period.

Sacrococcygeal teratomas have tissues derived from ectoderm, mesoderm, and endoderm.2 Although their embryonic origin is still uncertain, they are believed to arise early in gestation (at around the late second or early third week) from the totipotential cells of Hensen's node (also called the primitive knot), a remnant of the primitive streak in the coccygeal region.5-7 The primitive streak appears as a linear thickening in the ectoderm at the caudal edge of the bilaminar embryonic disc. It usually diminishes in size, eventually disappearing after undergoing degenerative changes. As the mesoderm rapidly proliferates, the primitive streak comes to lie more and more caudally, where the remnant of Hensen's node descends to the tip or anterior surface of coccyx.5-7