3D-printed models assist complex brain surgery for encephalocele

Encephalocele 3D printing

At five months’ gestation, Bentley Yoder was given little chance to live. A routine 20-week “gender reveal” ultrasound showed that a large portion of his brain was growing outside of his skull, a malformation known as an encephalocele. But he was moving and kicking and had a strong heartbeat, so his parents, Sierra and Dustin, carried on with the pregnancy.

Born through a normal vaginal delivery (the doctors felt that a C-section would interfere with Sierra’s grieving process), Bentley surprised everyone by thriving and meeting most of his baby milestones.

But the large protuberance on his head was holding him back. It steadily got larger, filling with cerebrospinal fluid. Bentley couldn’t hold his head up for more than a few seconds.

Encephalocele 3D printing

He went from hospital to hospital in his home state of Ohio. The neurosurgeon at the regional children’s hospital was confident he could remove the encephalocele, believing it to be damaged, nonfunctional tissue. But his parents suspected that Bentley might actually be using that displaced tissue.

A second opinion

Neurosurgeon Violette Recinos, MD, at the Cleveland Clinic agreed. She offered to operate, but also told the Yoders that she knew surgeons at Boston Children’s Hospital who were very experienced with encephaloceles.

That jived with the Yoders’ online research. They traveled to Boston, where plastic surgeon John Meara, MD, and neurosurgeon Mark Proctor, MD, in Boston Children’s Craniofacial Program outlined how they would approach Bentley’s case. Rather than cut the encephalocele off, they would drain the fluid and ease the brain tissue back into Bentley’s skull.

“We believe it’s actually functional brain tissue that’s going to be very important for him to maintain a normal quality of life,” said Proctor several days before surgery. “So we have to protect that brain tissue and find room in the skull to get it inside and covered up safely.”

The obvious challenge was that Bentley’s skull was too small.

“When you look at the size of the skull and how much brain is outside and how much is inside, we will have to expand his skull by about 20 percent,” said Meara.

The operation also posed several serious risks. The brain tissue was going to be shifted up 4 to 6 inches and spatially reoriented. Injury to any of the vessels feeding the brain could cause a stroke, and there could be significant blood loss. The slowly expanding fluid would likely require a drain and possibly a second operation to place a permanent brain shunt.

Modeling an encephalocele in 3D

The Craniofacial Program was an early adopter of 3D printing technology, collaborating closely with Boston Children’s Simulator Program (SIMPeds). SIMPeds engineers can quickly produce life-sized models of patients’ anatomy — “anatomy that typically they’d have to wait to get to the operating room to really get their hands on,” says SIMPeds director Peter Weinstock, MD, PhD.

The models allow surgeons to “do the operation before the operation” as Weinstock puts it — most famously to plan craniofacial surgery for Violet Pietrok, a toddler with a Tessier facial cleft.

In Bentley’s case, the models were especially intricate. They included a skull model made from rigid material that captured the thickness, edges and shapes of Bentley’s skull bones. The brain was printed with a soft material mimicking its natural consistency.

“We were able to print in two materials at once, in place, to show the surgeons exactly where the brain and skull were in relation to each other,” said SIMPeds engineer Noah Schulz (below). “Working with our radiologist, we started with the CT and MR images and segmented the images to build the individual models.”

Encephalocele 3D printing

The surgeons rehearsed a technique for expanding Bentley’s skull, called a barrel stave osteotomy. “You literally cut the bone as if you’re creating barrels to widen out the cranial vault,” Proctor explained. “The cut sections all remain connected at the base, so it gives you a lot more room without actually detaching the bone.”

Another print modeled the encephalocele as a whole, indicating the edges of the cerebrospinal fluid in relation to the other tissue.

“The models allow me actually to see and feel in three dimensions where the tissue is outside the skull,” said Meara. “You get a good idea of how the skull is flatter on one side, more prominent on the other, and the relative amount of volume.”

encephalocele 3D printing

SIMPeds also printed a removable rigid model of the dura — the membrane covering the brain — so Proctor could practice sealing it.

Since the encephalocele kept growing and changing, Proctor and Meara got fresh models to practice with just a week before Bentley’s operation. The preparation, they hoped, would shave hours off surgery and minimize time on general anesthesia, which poses neurocognitive risks for young children.

In the OR

The anesthesia team, led by attending anesthesiologist Susan Goobie, MD, had done extensive preoperative planning of its own. The encephalocele posed a challenge in terms of positioning Bentley’s head for intubation. Blood loss was another concern, so the team placed intravenous lines under ultrasound guidance to monitor and treat it. They used several techniques to conserve Bentley’s blood supply, including a medication called tranexamic acid that Goobie has shown to significantly decrease blood loss and the need for transfusion during complex cranial surgery.

When the surgeons scrubbed in, the 3D models came with them. “We had three models of the skull alone, the skull with brain, and the skull with the entire encephalocele that we constantly referred to,” says Proctor. “We were able to save the vast majority of the brain and achieved an excellent closure.”

For this last step, the surgeons used the strips of bone they’d cut out to expand Bentley’s skull and crisscrossed them over the top.

The operation was completed in less than five hours, as compared with 10 or more anticipated. Bentley remained stable throughout.

Two days later, as the surgeons had anticipated, Bentley needed a second operation to place a brain shunt. His brain was still producing excess fluid, causing pressure to build up inside his head.

Once the shunt was placed, Bentley almost immediately seemed more alert, curious and interactive. He was discharged on June 8, exactly two weeks after his operation.

encephalocele Bentley Yoder

Bentley goes home

Bentley will be followed by neurologists at home in Ohio. He may have ongoing vision problems as well as cognitive and motor delays.

“Because Bentley’s case is so unique, we’re somewhat unsure of what the future’s going to hold for him,” says Proctor. “Exactly how this encephalocele will impact his neurocognitive development as he gets older is a question only time is going to tell us. But we feel that we have given him the best chance, and I am certainly optimistic that he could have a rewarding life.”

“We were expecting good, but we didn’t expect him to be as good as he is,” said Sierra as the Yoders prepared to leave Boston. “We’re waiting to see what he’ll give us, and we’ll be happy with anything he does give us.”

Follow Bentley’s journey and learn more about SIMPeds and Boston Children’s Cleft and Craniofacial Center

If you are a physician with a complex case to refer, call Boston Children’s priority line (1-844-BCH-PEDS).