Fetus Removed From Brain of 1-Year-old Girl

A very rare intraventricular fetus-in-fetu was surgically removed from a 1-year-old girl with motor delay and an enlarged head circumference, a report from China showed.

The fetiform mass was a malformed monochorionic diamniotic twin, reported Chunde Li, MD, of Beijing Tiantan Hospital, and co-authors in Neurology.

Genetic sequencing showed identical single-nucleotide variants in the host child and fetus-in-fetu, with the fetus-in-fetu having extensive de novo copy number gains. The extensive de novo copy-number gains suggested the significance of copy-number variation during embryogenesis, the researchers noted.

“The intracranial fetus-in-fetu is proposed to arise from unseparated blastocysts,” Li and colleagues wrote. “The conjoined parts develop into the forebrain of host fetus and envelop the other embryo during neural plate folding.”

Fetus-in-fetu is a rare anomaly in which a vertebrate fetiform mass is found inside the body of a twin. It occurs in roughly one in 500,000 live births, often in the retroperitoneum of infants. A case of a fetus growing inside the abdomen of a young boy was described as early as 1808.

About 200 fetus-in-fetu cases have been reported in the literature, but very few have been intracranial.

Fetus-in-fetu cases can be misdiagnosed as teratomas. “Fetus-in-fetu can be distinguished from teratomas based on the younger age of presenting patients and the presence of vertebrae or internal organs,” Li and co-authors noted.

In this case report, a 1-year-old girl presented with motor delay; she was unable to sit independently. On examination, she had an enlarged head circumference of 56.5 cm. She had no sign of intracranial hypertension (nausea, vomiting, irritability, or deviated downward eyes) and exhibited full range of motion in four extremities with normal muscle tone.

Head CT and MRI revealed that the infant girl had hydrocephalus, a compressed brain, and an intraventricular fetiform mass. The mass had a vertebral column, femur, and tibia. Imaging showed the fetus-in-fetu had spina bifida; when further examined, it also had upper limbs and finger-like buds.

Intracranial cases reported in recent years include a fetus-in-fetu with well-developed organs in Thailand and one that was removed from a 5-year-old child in India. Fetus-in-fetu has developed in other unusual parts of the body, including the scrotal sac of an infant boy.