Fetus in fetu

[3] A fetus in fetu can be considered alive, but only in the sense that its component tissues have not yet died or been eliminated.

Thus, the life of a fetus in fetu is akin to that of a tumor in that its cells remain viable by way of normal metabolic activity.

However, without the gestational conditions in utero with the amnion and placenta, a fetus in fetu can develop into, at best, an especially well differentiated teratoma; or, at worst, a high-grade metastatic teratocarcinoma.

In terms of physical maturation, its organs have a working blood supply from the host, but all cases of fetus in fetu present critical defects, such as no functional brain, heart, lungs, gastrointestinal tract, or urinary tract.

The parasitic twin is anencephalic (without a brain) and lacks some internal organs, and as such is unable to survive on its own.

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 from the previous image shows a fairly well developed fetus lying on its back, with rudimentary digits.
A computed tomography scan of the same patient's abdomen pre-operation reveals a large retroperitoneal soft-tissue mass. There are long hyperdense opacities that resemble fetal bones.