A Human Fetus Was Removed From the Brain of a One-Year-Old Girl

Medical professionals at Beijing Tiantan Hospital recently documented an extraordinary case involving a one-year-old girl who underwent surgery to remove a malformed fetus from her brain. According to a case report published in the journal Neurology, surgeons successfully extracted what they identified as a “malformed monochorionic diamniotic twin” from the child’s brain.

Such occurrences remain extremely rare in medical literature, with an estimated frequency of just one in 500,000 live births. Most medical practitioners may never encounter such a case during their careers, making each documented instance highly valuable for scientific understanding.

Medical researchers consider this case particularly significant because it is located within the brain rather than in more commonly documented areas such as the abdominal cavity. Each new case reveals additional information about human development and potential anomalies during early pregnancy.

Behind an Enlarged Head

The parents first brought their daughter to medical attention due to developmental delays. At one year, she still could not sit independently, a milestone typically achieved between six and eight months of age. During the initial assessment, doctors immediately noticed her abnormally enlarged head circumference, measuring 56.5 centimeters.

Despite her significant head enlargement, she showed no classic signs of intracranial hypertension typically associated with such findings. Medical records indicate she did not experience nausea, vomiting, irritability, or downward deviation of her eyes. Full range of motion remained present in all four extremities with normal muscle tone.

Her physicians proceeded with standard diagnostic protocols, ordering computed tomography (CT) and magnetic resonance imaging (MRI) scans. Results revealed hydrocephalus—a buildup of fluid within brain cavities—alongside a compressed brain structure. Most significantly, imaging clearly showed an unexpected mass within her brain ventricles.

Further analysis of scan results led to a surprising discovery—what appeared to be skeletal structures visible within the mass. Medical professionals identified what looked remarkably like vertebrae and limb bones developing inside the young girl’s brain.

Twin Within a Twin

Medical literature refers to this phenomenon as “fetus in fetu” or sometimes “parasitic twin,” terms describing a condition where one developing embryo becomes enveloped by another during early pregnancy. In such cases, one twin absorbs the other, with the development of the absorbed twin typically halting while its sibling continues normal growth.

Unlike conjoined twins, who develop as partially separated individuals, fetus-in-fetu cases involve one embryo becoming entirely encapsulated within the body of another. Medical professionals must differentiate this condition from teratomas—tumor-like growths containing various tissue types. While visually similar, these two conditions have distinct origins.

According to medical experts quoted in the case report, fetus-in-fetu typically differentiates from teratomas based on two key factors: patient age at presentation (normally younger) and identifiable vertebrae or internal organs within the mass. Distinguishing between these similar-appearing conditions proves crucial for appropriate treatment approaches.

In monochorionic diamniotic twins like those in this case, siblings share a single placenta but develop within separate amniotic sacs. These twins would have been genetically identical from a single fertilized egg. Medical understanding suggests that somewhere very early in development, separation failed to complete properly, leading to one embryo developing abnormally within the other.

Most documented cases result in the absorbed twin appearing in the host’s abdomen. What makes this case particularly remarkable is its intracranial location—a finding seen in only a tiny fraction of an already exceedingly rare condition.

Medical Findings Inside the Brain

Detailed imaging revealed surprisingly developed structures within the brain mass. Medical professionals identified a vertebral column with two distinct leg bones—the femur (thigh bone) and the tibia (shin bone). Upon surgical removal and further examination, medical personnel also discovered upper limbs and finger-like projections developing within the mass.

Led by Dr. Chunde Li and colleagues, the medical team faced a challenging situation requiring precise diagnosis and careful surgical intervention. Their work adds to a minimal body of knowledge about intracranial fetus-in-fetu cases, with fewer than 20 reports published worldwide.

Additionally, doctors noted that the fetal mass exhibited spina bifida, a condition where part of the spinal cord remains exposed rather than adequately covered by tissues of the back. Such a finding suggests abnormal neural development within the parasitic twin, further complicating a complex case.

Given its location within the brain ventricles, surgical removal required extraordinary precision. Medical teams needed to carefully extract the mass while avoiding damage to surrounding neural tissues crucial for normal brain function. Neurosurgeons likely employed specialized microsurgical techniques during this delicate procedure.

Medical literature regarding similar cases suggests that surgical removal of such masses generally carriesa good prognosis when performed successfully. However, long-term developmental outcomes may vary significantly based on several factors, including age at detection, surgical approach, and any residual effects on brain development.

Advanced surgical navigation systems and high-resolution imaging capabilities available at major medical centers have significantly improved surgical outcomes for rare cases compared to earlier medical history. Modern surgical approaches focus on minimizing trauma to healthy surrounding tissues while achieving complete removal of anomalous structures.

Extremely Unusual Location

Among approximately 200 documented fetus-in-fetu cases throughout medical history, brain cases constitute a tiny subset. Finding such a mass within cranial cavities significantly differs from typical presentation, requiring specialized neurosurgical expertise for management.

According to medical literature, most cases—approximately 80%—occur in retroperitoneal areas, specifically within abdominal regions behind significant organs. Several theories attempt to explain why most cases manifest abdominally rather than cranially. Some medical researchers suggest that developmental processes may make certain body regions more susceptible to incorporating embryonic tissue during early development. Others propose that physical constraints during early gestation might influence the final placement of absorbed embryonic material.

Recent medical literature has documented unusual presentations in various body regions, including one case involving a fetal mass within a young boy’s scrotal sac. Each atypical location provides additional insights into developmental anomalies while challenging existing medical understanding.

For neurosurgeons encountering intracranial cases, treatment approaches must balance complete removal against preservation of vital brain structures. Surgical planning requires careful consideration of both immediate surgical risks and long-term developmental impacts on young patients.

Origins at Earliest Stages of Life

Medical experts believe this phenomenon originates during very early embryonic development—specifically at the blastocyst stage when fertilized eggs form clusters of cells that eventually develop into fetuses. According to researchers involved in this case, “intracranial fetus-in-fetu is proposed to arise from unseparated blastocysts.”

Under normal circumstances, identical twins form when a single fertilized egg splits into two blastocysts. In fetus-in-fetu cases, however, this separation likely remains incomplete, resulting in conjoined development. As case researchers describe, “conjoined parts develop into the forebrain of host fetus and envelop the other embryo during neural plate folding.”

Neural plate folding is a critical developmental process that forms the foundations of the brain and spinal cord. Disruptions during this crucial period can lead to various developmental anomalies, ranging from minor neural tube defects to significant structural abnormalities like those seen in this case.

Scientists can only hypothesize about the exact moments when developmental pathways diverged in such cases, as direct observation of such early human development remains impossible. Medical understanding relies heavily on careful examination of resulting abnormalities and knowledge of normal embryonic development timelines.

Modern embryologists continue studying factors influencing proper versus improper cell differentiation and migration during early development. Each documented case adds valuable information to the growing understanding of these complex biological processes.

Genetic Mysteries Revealed

In this case, genetic analysis yielded fascinating results with potential implications extending beyond this individual patient. Researchers found identical single-nucleotide variants in the host child and fetal mass, confirming their origin from a single fertilized egg—consistent with identical twin development.

More intriguingly, genetic sequencing revealed extensive “de novo copy number gains” within fetal mass DNA not present in the host child. Such findings suggest significant genetic alterations occurred during early development, potentially contributing to abnormal growth patterns observed.

The case authors noted that “extensive de novo copy-number gains suggested significance of copy-number variation during embryogenesis.” Such observations provide rare glimpses into the genetic mechanisms potentially underlying developmental anomalies during human embryonic growth.

Copy number variations—where sections of genetic material appear duplicated or deleted—play essential roles in normal development and disease processes. Studying these variations in rare developmental anomalies may offer insights applicable to more common developmental disorders.

Medical researchers increasingly recognize the importance of genetic factors in embryonic development. Modern sequencing technologies enable more detailed analysis than previously possible. Each analyzed case contributes valuable data points to the growing understanding of relationships between genetic variations and physical development.

Similar Cases Around the World

The medical literature contains approximately 200 documented fetus-in-fetu cases spanning centuries, with the earliest known description dating back to 1808. Historical accounts describe the removal of a fetal mass from the abdominal cavity of a young boy, demonstrating recognition of this phenomenon long before modern medical imaging or genetic testing.

In recent years, several noteworthy cases have been documented across different regions. Medical professionals in Thailand reported a case featuring unusually well-developed organs within an extracted fetal mass. Similarly, doctors in India documented the successful removal of an intracranial fetus-in-fetus from a five-year-old child.

Comparing cases across different populations and periods helps medical researchers identify potential commonalities and differences that suggest underlying causes or risk factors. Despite centuries of documentation, many questions remain regarding why such developmental anomalies occur.

Medical professionals approach each case with dual objectives: providing the best care for affected patients while carefully documenting findings to advance medical knowledge. Publishing case reports in peer-reviewed journals makes information available to the global medical community.

Collaborative international medical databases now allow tracking extremely rare conditions across geographic boundaries, potentially revealing previously unrecognized patterns. As reporting systems improve, medical understanding of even the rarest conditions increases incrementally.

Medical Significance Beyond Headlines

Beyond immediate surgical intervention, cases like these contribute significantly to medical understanding of human development. Each documented instance provides rare opportunities to observe developmental processes gone awry, potentially offering insights into normal developmental mechanisms.

Access to appropriate medical care profoundly affects outcomes for affected families. Early prenatal or infant screening detection allows for timely intervention before complications arise. Support services addressing developmental needs remain essential for long-term well-being.

Medical education benefits tremendously from documenting rare cases. Case reports prepare future physicians to recognize unusual presentations they might otherwise miss. They serve as valuable teaching tools in medical schools and continuing education programs.

Parents who notice developmental delays or unusual physical findings should seek prompt medical evaluation. While conditions like fetus-in-fetus remain extraordinarily rare, addressing developmental concerns early consistently leads to better outcomes regardless of a specific diagnosis.