An extremely rare congenital anomaly, intraventricular foetus-in-fetu, was recently surgically removed from the brain of a 12-month-old girl with motor delay and an enlarged head circumference – something that occurs in only about one in 500 000 live births, reports Medpage Today.
The fetiform mass was a malformed monochorionic diamniotic twin, reported Dr Chunde Li of Beijing Tiantan Hospital and co-authors in the journal Neurology.
Genetic sequencing showed identical single-nucleotide variants in the host child and foetus-in-fetu, with the latter having extensive de novo copy number gains (genetic alterations). These suggested the significance of copy-number variation during embryogenesis, the researchers noted.
“The intracranial foetus-in-fetu is proposed to arise from unseparated blastocysts,” Li and colleagues wrote.
“The conjoined parts develop into the forebrain of the host foetus and envelop the other embryo during neural plate folding.”
Foetus-in-fetu is a rare anomaly in which a vertebrate foetiform mass is found inside the body of a twin. It’s seen only in one out of about half a million live births, often in the retroperitoneum of infants.
A case of a foetus growing inside the abdomen of a young boy was described as early as 1808.
About 200 cases have been reported in the literature, but very few have been intracranial.
Foetus-in-fetu cases can be misdiagnosed as teratomas. “Foetus-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 one-year-old girl presented with motor delay; she was unable to sit independently.
On examination, she had an enlarged head circumference of 56.5cm. 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 she had hydrocephalus, a compressed brain, and an intraventricular foetiform mass. The mass had a vertebral column, femur and tibia. Imaging showed the foetus-in-fetu had spina bifida; when further examined, it also had upper limbs and finger-like buds.
Intracranial cases reported in recent years include one with well-developed organs in Thailand and another that was removed from a five-year-old in India.
Foetus-in-fetu has developed in other unusual parts of the body, including the scrotal sac of an infant boy.
Study details
Teaching NeuroImage: Intraventricular Fetus-in-Fetu With Extensive De Novo Gain in Genetic Copy Number
Zongze Li, View ORCID ProfileLi Ma, Yuanli Zhao, Chunde Li
Published in Neurology on 28 February 2023
Abstract
An intraventricular foetus-in-fetu, a malformed monochorionic diamniotic twin, was identified in a 1-year-old girl with motor delay and enlarged head circumference. After surgical removal, whole-genome sequencing revealed identical single-nucleotide variants in the host child and foetus-in-fetu, with extensive de novo copy number gains in the foetus-in-fetu, suggesting the significance of copy number variation during embryogenesis.
The intracranial foetus-in-fetu is proposed to arise from unseparated blastocysts. The conjoined parts develop into the forebrain of host foetus and envelop the other embryo during neural plate folding.1 Foetus-in-fetu can be distinguished from teratomas based on the younger age of presenting patients and the presence of vertebrae or internal organs.
foetus in boy
Neurology article – Intracranial fetus-in-fetu identified in child with motor delay (Open access)
Medpage Today article – Fetus Removed From Brain of 1-Year-Old Girl (Open access)
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