When a two-year-old girl arrived in Quebec with a skull nearly the size of a basketball, doctors knew they had a rare case on their hands.

Doctors don't often see such extreme cases of hydrocephalus in North America, where health practitioners typically intervene earlier.

In the case of this little girl, so much fluid had accumulated in her brain that it had forced her cranium to become deformed and grow abnormally large. Her head was so heavy that she was unable to lift it on her own. There was a risk of her neck snapping under the weight. And there was pressure building up in her cranium.

Using a 3D-printed model, some 210 screws and a black pen, surgeons undertook a risky 12-hour operation to reduce the size of the toddler's skull and allow her brain to grow.

The child, whom CBC News has agreed not to name to protect the family's privacy, was born in a country in North Africa and arrived in Quebec last year.

The damage to her brain is certainly major. - Dr. Alexander Weil , pediatric neurosurgeon

Montreal surgeons examined her and discovered her cranium was filled with about three litres of fluid (roughly 20 times the amount in a healthy adult) and had grown to 71 centimetres in circumference.

Pediatric neurosurgeon Dr. Alexander Weil placed an internal shunt in her brain to help drain the excess fluid.

But the effect was minimal.

"It was like sticking a straw in a pool," said Weil, of Montreal's Sainte-Justine Hospital.

The surgery at Sainte-Justine Hospital in Montreal lasted 12 hours. (Radio-Canada)

In addition to her physical limitations, the two-year-old had developmental delays because her brain had atrophied under the pressure of the excess liquid, to the point its volume was 80 per cent less than a normal one for her age.

"The damage to her brain is certainly major," Weil said.

While no surgery would be able to fully restore the child's neurological functions, Weil was sure he could give her a better life.

But it would take what he called a "drastic procedure" to reduce the size of her skull.

The plan was to take apart her skull and then piece it back together — like a puzzle — to make it smaller.

CBC/Radio-Canada's French-language TV program Découverte had exclusive access to the operating room during the procedure.

No guarantees

Weil teamed up with plastic surgeon Dr. Daniel Borsuk, as well as engineers in a lab in Michigan, to prepare for the challenging procedure.

Before entering the operating room, the team created a 3D virtual mock-up of how the skull could be reconstructed.

"We took the skull of the patient, we put it in [virtual ] pieces, and we found the best way to reduce the volume and the shape of the skull using those pieces," Borsuk explained.

The Quebec surgeons teamed up with engineers in Michigan, who helped them prepare a virtual mock-up of the skull reconstruction. (Radio-Canada)

The surgeons' plan was to reduce the size of the girl's cranium by 60 per cent.

"It would be impossible to make the shape of the skull normal. That's not our goal. Our goal is to give this child the best chance at having as normal a life as possible," Weil said.

"Will the operation guarantee that? Definitely not. But it will definitely increase her chances."

No room for error

On November 5 at 11:05 a.m. Borsuk prepared for the first incision. Despite all the preparations, there were still plenty of risks.

The first step was to make an incision from one ear to the other, to expose the skull.

This cutting guide — which looks like a plastic helmet — was created on a computer and printed in 3D to help the surgeons in the risky procedure. (Radio-Canada)

When they cut through the child's skull, the surgeons had to be careful to not hit blood vessels directly beneath. Any obstruction or damage to the brain's superior sagittal sinus — which allows the brain's hemispheres to drain — could cause cerebral hemorrhaging.

Once the skin was removed and the skull exposed, something that looked like a plastic helmet was brought over to the operating table.

It was the key to the entire procedure — a cutting guide, created on a computer several weeks earlier by the American engineers, and printed in 3D.

The surgeons used the guide and a black pen to trace the path they would cut, dividing the top half of child's skull into 12 pieces. As each piece was cut, it was placed on an adjacent table, where all 12 pieces would later be reassembled into a new, smaller skull.

After several hours, the girl's brain was fully exposed.

That's when the riskiest part of the procedure began: draining the fluid.

Weil removed the liquid slowly, at a speed of about 10 millilitres per minute, or about half a litre per hour. Moving any faster would have posed unnecessary risk.

CBC/Radio-Canada's French-language TV program Découverte got exclusive access. 0:56

Weil said he was able to remove about half of the liquid that had accumulated, about one and a half litres.

"For us, the worry is that if we take away too much liquid all at once, it will greatly increase the complications and risk of complications," he said.

The final step was to place the reconstructed skull back on the girl's brain. To fix it in place, the team used 210 screws, which will degrade in the span of a year and be absorbed by the body.

The two-year-old recovers in intensive care after doctors took apart and reconstructed her skull. With her are surgeons Dr. Daniel Borsuk, left, and Dr. Alexander Weil, right. (Radio-Canada)

The operation lasted 12 hours, and the child was taken to intensive care to recover.

Two weeks later, an MRI confirmed the surgery was a success: her brain had nearly doubled in volume.

Now that the girl's brain was unburdened from the excess fluid, her surgeons have hope the child's neural networks will reorganize themselves, and that she'll some day be able to play like other kids her age.