A very rare intraventricular fetus 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 child host and fetus-in-fetus, and fetus-in-fetus had large de novo copy number gains. The large gains in de novo copy number suggested the importance of copy number variation during embryogenesis, the researchers noted.
“Intracranial fetus-in-fetus is proposed to arise from unseparated blastocysts,” Li and colleagues wrote. “The attached parts develop in the forebrain of the host fetus and envelop the other embryo during the folding of the neural plate.”
Fetus-in-fetu is a rare anomaly in which a vertebrate fetiform mass is found within the body of a twin. It occurs in about one in every 500,000 live births, often in the retroperitoneum of infants A case of a fetus growing within the abdomen of a young child was described. already in 1808.
About 200 cases of fetus-in-fetu have been reported in the literature, but very few have been intracranial.
Cases of fetus-in-fetu can be misdiagnosed as teratomas. “Fetus-in-fetus 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 could not sit up independently. On examination, she had an increased head circumference of 56.5 cm. She had no signs of intracranial hypertension (nausea, vomiting, irritability, or downward wandering eyes) and she displayed full range of motion in all four limbs with normal muscle tone.
Head CT and MRI revealed that the girl had hydrocephalus, a compressed brain, and an intraventricular fetiform mass. The mass had a spine, femur, and tibia. The images showed that the fetus in fetus had spina bifida; when examined further, it also had finger-like upper limbs and buds.
Intracranial cases reported in recent years include a fetus-in-fetu with well-developed organs in Thailand and one that was taken from a 5 year old In India. Fetus-in-fetu has developed into other unusual parts of the body, including the scrotal sac of an infant boy.
This project was supported by the National Natural Science Foundation of China.
The authors did not report relevant disclosures.
Reference source: Li Z, et al “Neuroimaging Teaching: Intraventricular Fetus-in-Fetus with Large De Novo Gene Copy Number Gain” Neurology 2023; DOI: 10.1212/WNL.0000000000201578.