Sacral-teratoma/sacrococcygeal teratoma is a derivative of

Ans: A Primitive streak(Ref: Textbook of Human embryology 8th/e p.671)Gastrulation & Hensen's node:In 2nd week - Gastrulation occurs ---> Establishes 3rd germ layer (mesoderm).Gastrulation begins with primitive streak formation in caudal region of epiblast.Primitive node or Hensen's node or primitive knot:Thickening formed at cranial end of primitive streak.Sacrococcygeal formation:Failure of Hensen's node to regress can lead to sacrococcygeal formation.Incomplete primitive streak regression - leaves caudal remnant - Sacrococcygeal teratoma.Arise from residual to totipotential cell rests (Hensen's node).Sacrococcygeal teratoma demonstrates tissue derived from all three cell layers.Contain varying propoions of mature & immature elements.