A one-year-old girl underwent surgery to remove a mass from her brain, revealing a rare condition known as "fetus in fetu." This phenomenon occurs when one fetus is enclosed within another during development. In this case, the mass, measuring approximately four inches, contained upper limbs, bones, and fingernails, indicating it had been growing for months inside her cranial cavity. ​

 A one-year-old girl underwent surgery to remove a mass from her brain, revealing a rare condition known as "fetus in fetu." This phenomenon occurs when one fetus is enclosed within another during development. In this case, the mass, measuring approximately four inches, contained upper limbs, bones, and fingernails, indicating it had been growing for months inside her cranial cavity. ​

Fetus in fetu is a very rare occurrence, with only around 200 documented cases. It typically arises from the incomplete separation of identical twins during early development. One theory suggests that the healthier twin connects to the mother's placenta, while the smaller twin attaches to the larger twin's blood vessels. As the larger twin grows, it absorbs the smaller one into its body. ​

The girl was admitted to the hospital due to motor skill issues and an enlarged head. CT scans revealed the fetus in fetu pressing against her brain, leading to hydrocephalus - a condition characterised by fluid accumulation in the brain. This resulted in an enlarged head, excessive drowsiness, and seizures. 

The absorbed fetus survived for a year post-birth by sharing a blood supply with its sibling.

Surgeons carefully removed the mass during a complex and delicate operation, aware that even the slightest error could cause permanent neurological damage. The procedure required a multidisciplinary team of neurosurgeons, pediatric specialists, and anesthesiologists working together for hours. Once the mass was extracted, doctors were able to confirm that it was not a tumor, but a malformed parasitic twin—making the case even more extraordinary.

Following the surgery, the child was placed under close medical observation. Doctors monitored her brain pressure, motor functions, and neurological responses to ensure there were no complications. Gradually, her symptoms began to improve, with reduced seizures and better alertness, offering hope that early intervention had prevented long-term damage.

Cases of fetus in fetu occurring inside the skull are exceptionally rare, as most documented cases are found in the abdomen. Intracranial occurrences pose a much higher risk because of the limited space and the critical nature of brain tissue. This rarity made the case valuable for medical research and education, providing insight into early embryonic development and rare twin anomalies.

Medical experts emphasize that fetus in fetu is often mistaken for teratomas—tumors that can contain hair, teeth, or bone—but the presence of organized structures like limbs and fingernails distinguishes it as a parasitic twin. This distinction is crucial, as it affects both diagnosis and treatment planning. Advanced imaging techniques such as CT and MRI scans play a vital role in identifying these differences before surgery.

Today, the case continues to be discussed in medical journals and conferences due to its rarity and complexity. It highlights both the incredible unpredictability of human development and the life-saving potential of modern medicine. For the child and her family, the successful surgery marked not only the end of a medical mystery, but the beginning of a chance at a normal, healthy life.