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Conjoined twins separated: the science behind the success

Conjoined twins separated: the science behind the success

Posting in Science

The remarkable biomedical story behind the series of surgeries that involved separating the Sudanese twins' blood flow to and from their brains.

Twin girls joined at the head were successfully separated by a team of over 15 doctors after a series of surgeries in London ending last month. Here’s how they did it, New Scientist reports.

Rital and Ritag Gaboura from Sudan were born joined at the head. When they were 8 months old, surgeons began dividing the blood vessels in their brains. Now, each child is getting the blood she needs and draining blood from her brain properly.

1. First, the surgeons looked at the twins’ skulls and brains. Using MRI and CT scans, they showed that the skulls were fused… but the girls didn’t share a brain.

Craniopagus twins sharing a skull but not a brain are rare, occurring about once in every 2.5 million births. Surgery is usually too risky if brains are joined.

Next, the surgeons need a physical 3D model of the skull and brains to study the network of arteries and veins transporting blood to and from their brains.

In many cases, their veins are tangled, with some running from one’s brain to the other’s – having to separate veins becomes a major obstacle. (If one ends up with too many veins, the heart could collapse; if one has too few, the brain will swell with blood.)

"It really comes down to the investigations of the blood vessels and how you make decisions about where to cut,” says Richard Hayward of Great Ormond Street Hospital, where the surgeries were performed.

To model blood flow, they injected dyes into the twins’ arteries and traced the blood’s path in and out of the brain with a rapid series of X-rays.

Glassworks Amsterdam, a media production company, used the images to make a CGI video of the blood flow. Cavendish Imaging, anatomical imaging specialists, printed a 3D model of their skulls, along with skin, bone, and blood vessels.

2. In May this year, the surgeons began dividing the veins in the brains.

There are 2 major venous systems draining blood from the brain: a superficial system in the tissue surrounding the brain and a deeper one in the internal brain structures.

They wanted to give one twin most of the superficial system and the other most of the deep system… both brains should adapt to the loss by expanding smaller blood vessels that connect the two systems.

They drilled a window in the twins’ skulls – using a high-speed craniotome equipped with a foot-like part that pushes the brain out of the way.

After slicing through the veins, they tied those off with ligatures and dissolvable sutures. Whenever possible, shared veins were split at a junction, giving each twin one part. Sometimes, the surgeons placed a sheet of non-stick material between the 2 brains, keeping veins and tissues separate during recovery.

3. The final hurdle: craniopagus twins don’t have enough bone and skin between them to form complete skulls and scalps when the time comes to sew them up.

In July, the surgeons put 4 silicone balloons underneath the twins’ scalps (between bone and skin), and slowly filled them with saline solution. The balloons gradually stretch the skin, giving the surgeons plenty of skin to work with for the final surgery.

To expand bone, the surgeons drove chisels between the 3 main layers of skull: the tough inner and outer layers and the spongy middle part. They split the bones and lifted up a section, doubling the original area. Dura, the protective tissue around the brain, regenerates bone in young children.

"One big operation risks the brain swelling and problems in reconstruction,” lead surgeon David Dunaway tells the BBC. "It's lots of simple steps, is any one step impossible? No. This is sure and steady, that's the elegance of the technique.”

The twins were finally separated in a 13-hour operation last month. UK charity Facing the World helped fund the 4-stage operation.

Via New Scientist.

Images: Facing the World

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Janet Fang

Contributing Editor

Janet Fang has written for Nature, Discover and the Point Reyes Light. She is currently a lab technician at Lamont-Doherty Earth Observatory. She holds degrees from the University of California, Berkeley and Columbia University. She is based in New York. Follow her on Twitter. Disclosure