Swollen belly JP/Panca Nugraha

A 10-month-old baby in Indonesia has undergone successful surgery to remove a parasitic twin from his abdomen.

The infant was admitted to West Nusa Tenggara Regional General Hospital in Mataram on the island of Lombok on 11 March after his belly expanded to the size of a cantaloupe.

His parents feared he had a tumour, but an abdominal CT scan and X-ray photos detected a fetus-shaped mass with the bony outline of a spine and limbs.


A team of doctors removed the mass on Saturday in a one-and-a-half hour procedure. “Our physician team has performed surgery on the baby and managed to remove a 400-gram fetus,” hospital director Lalu Hamzi Fikri announced in a press conference later that day. The baby is recovering well, he said.

Examination of the removed fetus revealed that it was male but not fully developed. This fits with previous descriptions of ‘fetus in fetu’ – an extremely rare condition in which one or more partially formed fetuses develop inside the body of another fetus.

Since the first documented case around 1800, there have been fewer than 200 reports of fetus in fetu globally. The miniature fetus usually has a spine, limbs and several organs, but not a brain or skull. It acts like a parasite, feeding off the blood supply of the larger fetus in which it is enclosed.

Parasitic fetuses have been found in several different body sites, including the abdomen, chest, skull, and scrotum. In one case reported in 2008, 11 fetal masses were found inside the abdominal cavity of a newborn baby in the US.

Parasitic twin

The condition arises when a twin is absorbed by another in the womb, says Mark Umstad at the Royal Women’s Hospital in Melbourne, Australia. This is only possible if the twin embryos originate from same egg and share the same placenta, he says.

Embryos start out as flat discs, but at 4 weeks of development, they begin to fold to form the basic body shape. The close proximity of identical twins means that one can sometimes be folded into the other during this process. Some experts believe that a twin is more likely to be absorbed in this way if it has an existing defect.

The location of the fetus in fetu depends on where it gets trapped during the folding process, Umstad says.

Advances in fetal ultrasound have made it easier to detect parasitic twins during pregnancy, allowing them to be surgically removed soon after birth. But sometimes they are not discovered until much later. For example, in the early 1990s, a fetus was found in the upper abdomen of an Italian man who was 47 years old.

The condition is often asymptomatic, but it can cause pain if the fetal mass pushes against the host twin’s internal organs. It can also lead to malnourishment because the trapped twin draws from the host’s nutrients.

It is possible that the incidence of fetus in fetu will increase as assisted reproductive treatments become more common, because they increase the chance of conceiving identical twins, says Umstad. “However, since fetus in fetu only occurs in about 1 in 500,000 births currently, we might be talking about one extra case a year globally,” he says.

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