Nineteen months ago, Erin and Abby Delaney underwent daring surgery at Children’s Hospital of Philadelphia to separate their conjoined heads.

Now 2½ years old, the twins are home in the Charlotte, N.C., suburb of Mooresville with their parents, Heather, 28, and Riley, 25. The girls’ weekdays revolve around physical, developmental, speech, and other therapies.

How are they doing? In a word, they are thriving, their parents and doctors agree.

“Erin is crawling everywhere, like it’s her mission,” their mother said. “She’s starting to pull herself up on things. She loves to reach up on the coffee table and grab the remote. Abby is sitting up on her own and rolls around. Somehow, she gets where she wants to be. She’s like, If I want that, I’m getting it.”

On Wednesday, the pigtailed redheads — stars of a “year in the life” YouTube video made by CHOP and viewed by more than eight million people — also became part of official medical literature. The New England Journal of Medicine published the CHOP team’s report of its innovative approach, elaborate planning, and climactic 11-hour surgery that freed the babies from each other.

Being published in a prestigious journal is exciting, said reconstructive surgeon Jesse Taylor and neurosurgeon Gregory Heuer, who led the team. But nothing compares with watching the steady progress of the twins, who have been back to CHOP three times for check-ups.

“I think they’re doing a lot better than we expected. They may have delays, but the separation process resets the developmental clock” back to birth, Heuer said. "We’re not sure how well they’re going to do ultimately, but that’s a good thing. When we [doctors] don’t have answers, that makes us feel good to some extent, because it tells us the door is wide open.”

Rarest of the rare

Heather Delaney with her daughters, Erin and Abby, at Children's Hospital of Philadelphia, before the twins were separated on June 6, 2017.
Children's Hospital of Philadelphia
Heather Delaney with her daughters, Erin and Abby, at Children's Hospital of Philadelphia, before the twins were separated on June 6, 2017.

Twins fused at the head, called craniopagus, are the rarest of conjoined pairs, occurring once in 2.5 million births. Only about 60 separations have been attempted since 1952. The world’s most experienced craniopagus surgeon, James T. Goodrich at Children’s Hospital of Montefiore in New York City, pioneered a staged approach that involves operating on each quadrant of the brain over about 10 months.

But Goodrich’s twins — including 4-year-olds Anias and Jadon McDonald, who have been followed by CNN —suffered persistent head wound healing problems and fluid buildup, called hydrocephalus. Erin and Abby have had no such complications.

Soon after Heather first consulted CHOP when she was about 12 weeks pregnant, Taylor proposed a way to jump start the separation. The technique, called distraction osteogenesis, was well-established for correcting cranial deformities, but had never been used in craniopagus separation. It capitalizes on the paradoxical fact that when a bone is cut and the two ends are slowly and gently tractioned apart, the process spurs bone growth as the tissue tries to heal.

The twins were just four months old when their skulls were cut at the junction point at the tops of their heads. They were fitted with custom-made, padded distraction devices that painlessly pulled their heads apart about seven-hundredths of an inch per day for two months.

CHOP plastic surgeon Jesse Taylor (left) and neurosurgeon Gregory Heuer used 3D plastic models to help plan the complex separation of the heads of twins Erin and Abby Delaney
JESSICA GRIFFIN / Staff Photographer
CHOP plastic surgeon Jesse Taylor (left) and neurosurgeon Gregory Heuer used 3D plastic models to help plan the complex separation of the heads of twins Erin and Abby Delaney

As the surgeons explained to the Inquirer in 2017 and now in the journal, this traction served several purposes. It improved the position of the twins’ heads, generated extra tissue that helped with later reconstruction, and, most important, created a one-inch open channel that provided more favorable access to cranial blood vessels.

Those vessels are a huge obstacle to surgical separation, even for twins like Erin and Abby, who shared only a small spot of brain tissue. Not only does cranial blood drain to supply other vital organs, but one twin — in this case Erin — has a disproportionate amount of vasculature. Dividing up this circulatory tissue is particularly risky and potentially debilitating for the shortchanged twin, in this case Abby.

The doctors decided to disconnect Erin and Abby at 10 months old — younger than any previous set of craniopagus twins — in hopes of capitalizing on the resilience, or plasticity, of infants’ brains. Theoretically, the team wrote in the journal, this would allow “recovery faster and more completely than at an older age.”

Illustration provided by the Children's Hospital of Philadelphia shows the procedure used to separate the Delaney twins.
CHOP
Illustration provided by the Children's Hospital of Philadelphia shows the procedure used to separate the Delaney twins.

But this theoretical advantage had to be weighed against a biological reality: “In infants … even modest blood loss can be life-threatening.”

Originally, the doctors planned to do a two-stage surgery, giving the babies three weeks to heal between procedures. The second stage would culminate with cutting a major vein, the sagittal sinus, that is a vital conduit for blood and cerebrospinal fluid.

But the first stage went off “without complications, with minimal blood loss, and in less than four hours,” they wrote in the journal. “Therefore, a decision was made to continue with separation ... without delay.”

Scientific journals try to be strictly factual and dispassionate, so this seven-hour second stage is described simply as “more complicated.”

But in 2017, the surgeons said, the race to keep up with the twins’ relentless blood loss during this second stage of the surgery was harrowing.

“If Abby’s bleeding had continued much longer,” Heuer said, “we could have lost her.”

No ‘What to Expect’ book

In a blog she has kept since she was pregnant with the twins, Heather, a former nanny, confided one of the hardest parts of her parental journey.

“There is no book to follow on this,” she wrote in September 2018. “I can’t read ‘What to Expect’ for toddlers because my toddlers are different.”

Abby (in purple) and her sister Erin had fun at Halloween, even though they have not developed a taste for candy or other foods
Courtesy of Delaney family
Abby (in purple) and her sister Erin had fun at Halloween, even though they have not developed a taste for candy or other foods

One difference is that even though Erin and Abby can swallow and digest food normally, they have no desire to do so. Almost everything they eat is pureed by their mother and injected into their stomachs through a tube that she connects to an access port in their abdomens.

“We’ve tried so many different foods, textures, sweet, savory, crunchy, puree, puffs, melts, teething biscuits, and nothing seems to really get them interested” in eating, Heather lamented.

Still, the twins’ growth is on track, and they’re about average in size for their age. Although neither is walking yet — a milestone normally reached around a year old — Erin’s ability to pull herself to stand against furniture is an encouraging transitional step. Both girls use therapeutic machines designed to help them learn to walk. Abby, whose setback was greater because she got less of the crucial vein, also hangs out in a standing support device that helps put weight on her legs to strengthen her muscles.

Abby's "stander" strengthens her leg muscles while she plays with toys or watches TV
Courtesy of Delaney family
Abby's "stander" strengthens her leg muscles while she plays with toys or watches TV

As for verbal communication, that is also lagging, but the twins seem to be on the cusp of breakthroughs.

“They say ‘Mama’ and ‘Dada,' but I don’t think they know what they’re saying yet,” Heather said. “According to the speech therapist, they’re doing advanced babbling, and they’ll even mimic sounds” when coached by adults.

There is no doubt about the twins’ ability to communicate without words.

“When Daddy walks in, they get so excited,” Heather said of her husband, who works for a shoe company. “If he gives one of them too much attention, the other one starts yelling and kicking. He gets the best giggles and smiles.”

Recently, Heather has noticed another telling interaction — between the sisters.

“Their cribs are placed head to head,” Heather explained. “Erin will crawl to the head of her bed and look down into Abby’s crib. And Abby will look up and smile.”