胎中胎

Anteroposterior abdominal radiograph shows a soft-tissue mass in the right hemiabdomen. The mass contains calcified osseous-appearing structures of varying sizes and shapes.

The postoperative specimen shows a fairly well developed foetus lying on its back, with rudimentary digits.

Computed Tomography scan of the patient's abdomen reveals a large retroperitoneal soft-tissue mass. There are long hyperdense opacities that resemble fetal bones.

胎中胎(Foetus in foetu或fetus in fetu)是一種在體內形成了類似胎兒的組織塊的發育異常。喬治·威廉·楊（George William Young）在1808年最早描述了這種現象。[1]

關於胎中胎的形成有兩種理論，一種理論認為，腫塊一開始是正常胎兒，但後來被包裹在其雙胞胎的內部。[2]另一個理論是，腫塊是高度發達的畸胎瘤。據估計，胎中胎在500,000例活產中有1例發生。[3]