New York (CNN) The surgical team labored for 27 painstaking hours to separate twins Jadon and Anias McDonald. The boys were born joined at the head. The surgery to separate them was rare and complicated.

The story of how they were separated in October at 13 months old captivated millions around the world.

The procedure, known as craniopagus surgery, is so rare that it has been conducted only 59 times since 1952. Jadon and Anias' surgery was the seventh performed by Dr. James Goodrich, who led the operation at the Children's Hospital at Montefiore Medical Center in the Bronx, New York.

CNN was allowed exclusive access to the surgery and the McDonald family, including the boys' parents, Christian and Nicole McDonald. The boys' surgery began the morning of October 13 and ended shortly before 1 p.m. October 14.

Nearly a month later, Goodrich said the twins were progressing "right on target, if not ahead of schedule," the lead neurosurgeon tells CNN. "As a neurosurgeon, I guess it puts you in a happy mood."

Goodrich and Dr. Oren Tepper, the lead plastic surgeon charged with reconstructing the boys' skulls, headed up a team of more than 30 people at Montefiore, from anesthesiologists and radiologists to nurse practitioners.

Here, for the first time, the surgical team describes in their own words the key moments inside the operating room and what it was like to be a part of such a rare surgery. The quotes have been edited for length and clarity.

'We would've lost one or both children'

Kamilah Dowling, pediatric neurosurgery nurse practitioner, with Dr. James Goodrich.

Goodrich said the "most unexpected surprise" came hours into the surgery, when the team learned that the boys' brains were fused more than they realized.

When the boys first arrived at the hospital months ago, the twins shared about 1.5 centimeters in diameter of brain tissue, but as they grew during their stay, so did the fused tissue. Going into the surgery, doctors believed the twins had about 3.8 centimeters in diameter of fused brain. Once they operated, they found that it was even larger.

"When we actually got in there, their brains were totally fused. It was a bigger fusion than we expected in the sense it was about 5 centimeters by 7 centimeters. For a child that size, that's a good chunk of tissue, but we had to separate them, and so to do that, it was a matter of just picking a plane between the two. Intraop, we'd done some beautiful imaging studies of the venous anatomy, but as has always been the case, when you get down in there, it's even more complex than you realized when you started.

"There was a very large venous complex that had a huge potential of bleeding, and if we lost control of that, we would've lost one or both children. I took in extra time, and we added another four hours onto the case to get the exposure, and we eventually found a nice window, which just kind of opened up, and we followed it down.

"The problem with these, these veins are abnormal. They're very thin, and if they rupture, you have no way of controlling them. It's a situation where you have to have total control all the way through, because once you lose it, you can't back off. I was at a point that I was wondering whether we were going to lose both kids if one of those things broke. Then again, after discussion with various members of the team, we picked an avenue that was safe -- and it worked.

"I'm just glad it wasn't my first craniopagus surgery. That would've been ominous. This is now our seventh set that we've separated. Every one of them had their own unique idiosyncracies. These kids, in the sense of the vascularity, I actually thought they were going to be simpler. Simpler is not the right word, but less complex than what we'd done before. But in actual fact, they turned out to be as equally complex as any of them. They were a challenge."

Pediatric neurosurgery nurse practitioner Kamilah Dowling stayed in touch with the parents throughout the surgery, updating them about every two to three hours. "I would text Nicole or give her a call. First, I would check with Dr. Goodrich to see where are we now, what are we doing, and this is what I am going to tell Nicole. If we were having blood pressure issues, anything that was going on at that moment, I would share with Nicole. I feel that we did our job as nurse practitioners. We supported the family from beginning to end. We'll continue to support them emotionally, anything they need."

'The biggest hurdle'

Dr. Oren Tepper, director of the craniofacial surgery program at Montefiore.

Tepper, the lead plastic surgeon during the operation, says he feels relieved at this point. He describes the pivotal moment of the surgery, when Goodrich studied the intricately fused brains and proceeded ahead.

"I mean, that was really the final decision point whether this was possible or not, and ultimately, Dr. Goodrich really was the one to make that decision. What it required was all of us putting our heads together and saying, 'Well, let's determine if we think this is possible.' That's where radiology became crucial. Dr. Joaquim Farinhas of radiology was essential looking at the anatomy. I think having the whole team there to say, 'This is what needs to be done. This is how we can approach it. This is what we need to get there.' It was really important that we were all there to make that decision and say, 'Well, this is the point of essentially no return.'

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"We knew their anatomy was complex. All the imaging that we had done beforehand tells you that. But until you're actually seeing and feeling the tissues, you cannot predict those moments. I think getting to that point and realizing that this was possible was incredible.

"For me, I think the big emotional change was when they were actually separated. I hadn't seen twins be separated before ... and for me, that final moment when we were able to take those two beds and separate them apart was like nothing else I've ever seen.

"I feel relieved at this point. I think there was a lot of concern, obviously, going in. We knew this was going to be a big undertaking, and I think things went as well as we could've hoped for at this point. I think that the biggest hurdle -- getting them through this operation safely and getting them separated -- we've gotten past. We're excited about that."

'Emotional toll on all of us'

Dr. Rani Nasser, chief neurosurgical resident.

Drs. Rani Nasser and Ajit Jada, chief residents of neurosurgery, have performed hundreds of surgeries, but nothing quite compared to the craniopagus surgery to separate Jadon and Anias. They said the success came down to "pure teamwork," with Goodrich leading the "orchestra." One of the trickiest moments for them came when the boys were rotated, and doctors were trying to determine whose vascularity was whose.

Nasser: "Because the brains fuse together, and it's really hard to know when Jadon ends and Anias begins. And that's really when we were wondering, 'Is this Jadon? Is this Anias?' Honestly, to this day, I think without 3-D modeling and printing, we would've not been able to decipher this as easily. It really was pure teamwork and having many sets of eyes on this.

"I've seen the boys grow up. I've literally seen them grow up. Half their lives, you know. Every time anesthesia raised a concern, we listened. And we listened, and we were frightened, but we were focused, and we worked together and gave each other strength to make it happen."

Jada: "I think the pivotal moment for me was when we had bleeding from the sides."

Nasser: "Right."

Jada: "Normally, you have time to control the blood. And these kids are small, and it was challenging, because we only had 10 seconds, basically, to control the blood before the pressure started going down."

Dr. Ajit Jada, chief neurosurgical resident.

Nasser: "If at all, right?"

Jada: "The anesthesiologists were saying 'pressure's 100 over 60, pressure's 60 over 50.' And you hear that going on."

Nasser: "The number's going down. ..."

Jada: "And you're reacting quickly to stop the bleeding at the same time. So that, I felt, was one of the most challenging aspects of the surgery. Or in general, any surgery I've ever done."

Nasser: "Every time we were over one obstacle, there were three others. With that perseverance, we were able to do it, but it definitely took an emotional toll on all of us."

'Please, let them see'

Esther Uy, a patient care coordinator with the department of neurosurgery.

Esther Uy, the patient care coordinator for neurosurgery, was in charge of five nurses and four surgical technicians during the operation. She's been at Montefiore for 34 years, and Goodrich credits her with helping his surgeries run smoothly. She describes her emotions when the surgeons reached the most critical juncture.

"All I was thinking was, 'Please, let them see where it is the right place to separate them.' That is most important. If they made a wrong move on where to cut or where to clip, it will be a disastrous result. But with the help of the models and Dr. Joaquim Farinhas showing Dr. Goodrich where to go, they were able to do it safely without disaster. That's the one that we were so afraid of. Any time, anything can happen, but Dr. Goodrich delivered.

"It is very rewarding to see them separate. It's a miracle already, to see them separated."

'Under the drapes'

Drs. Carlene Broderick, left, Glenn Mann and Madelyn Kahana, anesthesiologists.

Three anesthesiologists -- Drs. Carlene Broderick, Glenn Mann and Madelyn Kahana -- worked beneath the drapes to keep the boys alive throughout the procedure. The surgery took 27 hours, from the first cut to the last stitch. However, the anesthesiologists' job began three hours before the first cut as they prepped the children.

Broderick: "I was ecstatic to be involved with the McDonald twins' surgeries. I was involved with the Aguirre twins in 2004, so we knew we could do it. But this time, we had more confidence. In one word, the entire surgery was miraculous!"

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Kahana: "When the children are joined, they share circulation in some capacity, and invariably they share some commonality about the drugs that we give and, depending upon where they're joined, even the way we mechanically ventilate them during anesthesia. We have to know what each other is doing at all times, because what I would do for one twin would effect the child that Dr. Mann was caring for and vice versa. So communication was constant."

Mann: "We were always learning how that sort of interaction was happening from the first time we took care of them, straight through to the last time. It was always a little different. ...

"Going under the drapes is sort of what we do. The surgeons are above the drapes, and we're below the drapes, making sure the patient is safe. The most important thing is the maintenance of the airway, and we're constantly checking the airway, the breathing tube that both the boys have. Throughout the surgery, they were repositioned multiple times, and our job was to make sure that the tube didn't come out at any point, because that would just be a devastating thing to happen during the operation. That's one thing we're doing. At the same time, all our IV access and drugs that we're giving are under the drapes."

What was the most intense moment during the surgery?

Kahana: "It was all Anias. It seemed like every time Dr. Goodrich got anywhere near the dura (the outermost membrane that envelopes the brain), Anias' blood pressure plummeted. That happened over a fairly long period of time, because he was dissecting around the dura for hours. There were many times for, really fortunately, seconds that Anias' blood pressure would fall fairly precipitously and require multiple vasoactive substances being administered. We had probably about five hours of intermittent, fairly profound blood pressure changes to deal with to the point where Dr. Mann was refilling my syringes for me because I was going through them at such a fast pace.

"Sometimes, we just have to say, 'Stop or get control of the bleeding, hold pressure, give me a minute!' And that's what they do."

Building confidence

Dr. Joaquim Farinhas, neuroradiologist within the department of radiology.

Dr. Joaquim Farinhas, a neuroradiologist, was credited by many in the operating room as being the key in helping the surgeons navigate through what he called the "lake of veins." He deflects such praise, saying he was simply doing his job.

"It's a combination of what I provide them as a map and my confidence in their skills. I can tell them, 'Please, you know what's on the left side here. This is delicate; stay away from that side.' But they're the ones who are making that final decision. We're just trying to keep them on track and give them as much confidence as we can.

"I think that was the most important part. I had to take a role there, and that was my job, to give them the confidence. Dr. Goodrich cut that connection and had to be confident that it was going to be successful. And I think that worked out well."

When 'one turned into two'

Dr. Carrie Stern, a senior resident of plastic and reconstructive surgery.

Dr. Carrie Stern, senior resident of plastic and reconstructive surgery, participated throughout the surgery. She made the official final cut to separate the boys. At 2:11 a.m., the twins became officially separated. That was about 16½ hours into the surgery.

"All the difficult aspects of the surgery had been completed by the entire team -- from splitting the bone, the brain, all the difficult blood vessels that needed to be separated between Anias and Jadon -- and really the only part that remained was a small skin bridge. Dr. Tepper had asked, 'Who wants the final cut?' And I just seized the moment: Grabbed the scissors and cut.

"It felt good. It was exciting. It was amazing to see the two beds slowly pull apart. As Dr. Goodrich said, 1 millimeter at a time. It was just incredible to see the one turn into two."

'Very, very rewarding'

Dr. Michael Ushay, director of the pediatric critical care unit.

Dr. Michael Ushay, director of the pediatric critical care unit, says it was an awesome moment the first time the boys were in the same room "in separate beds and separated from each other."

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"This is pretty extraordinary. I remember when Dr. Goodrich did his last conjoined twins here, and that was before I'd actually come to Montefiore, and it was very, very exciting. Now, to be part of it on such a complicated case is very, very rewarding. I've always enjoyed working with kids through complex operations. This has got to be one of the most complex operations, and to have them come through it. When they're together and you're meeting them, you wonder, 'How are they ever going to do this?' But they did it. That was great. The kids look really good."