Fetus In Fetu: A Baby Inside Of Another

What is Fetus in Fetu?

“Fetus in Fetu” is a rare pregnancy complication in which a fetus (or a mass of tissue tightly resembling a fetus) is present inside of another fetus. Fetus in fetu can be characterized as being alive or dead: it is considered “alive” when the tissues of the inside fetus have a viable blood supply, and it is “dead” when the tissues are non-functioning. In viable fetus in fetu and depending on the level of development of the internal organs, the internal fetus can present with a fully functioning gastrointestinal tract, urinary tract or even respiratory tract. However, its survival is strictly dependent on the blood supply of its host twin.

Theories of Development

There are two main theories that have been postulated in attempt to explain the occurrence of this peculiar medical condition.

The Teratoma Theory: First, fetus in fetu could result from a highly differentiated teratoma: by definition, a teratoma is a germ cells tumor that features cells from the ectoderm, mesoderm and endoderm. Those three layers are the cornerstone, the rock from which all the organs and tissues are derived during fetal development. This would explain why on biopsy, a teratoma can display features such as hair, teeth, bone and blood vessels. Teratomas are benign tumors by default, but also have the possibility of being malignant.

The Parasitic Twin Theory: this is the second hypothesis that explains Fetus in Fetu. According to the Parasitic Twin Theory, during the early fetal development of monozygotic twins (those that share a placenta), one twin benefits from more blood supply than the other, and therefore grows faster and much better than the other. Eventually, due to the smaller size of the unfortunate twin, the dominant twin surrounds him and engulfs him. 

Fetus in fetu has made a lot of buzz in the social media, due to the rare yet fascinating character of this medical mystery. However, it is important to emphasize that the condition can be very dangerous for the twin who is carrying his parasitic twin inside of him; as it can cause compression of internal organs, internal bleeding and in the event that it is a malignant teratoma, it can result in accelerated cellular division and cancer metastasis.

The Difference between a Fetus in Fetu and a Teratoma

Some key differences between fetus in fetu and teratoma have been highlighted by several researchers to demonstrate that the condition (fetus in fetu) is indeed a truly isolated pregnancy complication that is not to be associated with teratomas.

See Also: Pregnancy: Recognizing The Symptoms Of Common Complications

That is, the risk of a fetus in fetu developing into cancer is extremely low, if not inexistent. In addition, fetus in fetu develop in the upper body, whereas teratomas tend to develop in the sacral and coccygeal regions. (Nevertheless, there is a possibility of fetus in fetu developing in the testes and the scrotum as well). Lastly, the presence of a vertebral column confirms the diagnosis of fetus in fetu, as teratomas do not present with vertebral column.

How Is Fetus In Fetu diagnosed?

According to Hoeffel et al., the majority of Fetus in Fetu cases are diagnosed in infancy, more specifically before the age of 18 months. The infants usually present with a visible and palpable abdominal mass. A CT scan of the abdomen generally confirms the diagnosis. However though, medicine always presents with exceptions. In fact, there have been cases of fetus in fetu diagnosed during teenage years and adulthood. In 2006 for example, a 36 years old man from India (Nagpur) was diagnosed with fetus in fetu after having lived for all these years with abdominal distension. But even in those settings, the physical presentation is the same: chronic and non-resolving abdominal pain for years, presence of an abdominal mass (not mandatory to make the diagnosis).

In adults who are diagnosed with the condition, they usually present to the hospital with complications of the condition, which leads to the diagnosis.

In the case of Sanju Bhagat (the abovementioned 36 years old Indian man), the parasitic twin had grown so big that it started compressing the diaphragm, causing breathlessness and other troubles breathing that prompted the patient to rush to the hospital. The patient had had a huge abdominal mass for his entire life. In other cases, the mass can compress the kidneys leading to kidney problems, the spleen (putting the patient at risk of internal bleeding) or even the internal vessels (abdominal aorta, mesenteric vessels), thus decreasing the blood supply to the intestines and the pelvis and putting the patient at risk of bowel infarction.

The most important imaging technique used to diagnose this condition is an abdominal CT scan. Specific findings have been described by Nocera et al; that are peculiar to the CT appearance of a fetus in fetu. This includes the presence of a mass that consists of a round or tubular collection of fat surrounding a central bony structure. More importantly, a vertebral column alongside with long bones should be identified to confirm the diagnosis. When the patient presents in an acute setting (like in the case of the 36 years old Indian man), the diagnosis can only be made post-operatively, after an exploratory laparotomy.

Treatment

The recommended treatment for fetus in fetu is surgical removal of the parasitic fetus. In patients that are diagnosed in adulthood, it is possible for them to develop a bond with their twin brother or sister, and they might refuse to proceed to the removal of their parasitic twin. However, care should be taken and adequate advice should be given regarding the benefits of doing the procedure and the risks of not doing it.

See Also: Placental Complications During Pregnancy And Birth

Fetus in Fetu in popular culture

As far as the medical literature is concerned, fetus in fetus was first described in the late 28^th century, by Meckel. As of 2000, there were 79 identified cases. However, this number has considerably increased since then. For instance, in September 2009, a toddler native of China (Kang Mengru) was diagnosed with the condition and underwent a 10-hours surgery to remove the parasitic twin. In 2008, Sam Esquibel (who was a toddler then) underwent brain surgery for the removal of a “foot” and other body parts growing in his brain. Several other cases of fetus in fetu are available in the medical literature.