Joanna Kemp, MD, spent nearly a year preparing for an operation she may never perform again.
The anatomy was extraordinarily rare. Two 2-year-old girls were conjoined at the head, with shared vascular structures that would have to be mapped and separated before the twins themselves could be.
On Feb. 24 and 25, surgeons at SSM Health Cardinal Glennon Children’s Hospital in St. Louis separated the twins in a procedure that lasted more than 24 hours from preparation through recovery. Their broader care involved more than 60 clinical team members.
For Dr. Kemp, director of pediatric neurosurgery at St. Louis-based SSM Health Cardinal Glennon Children’s Hospital and associate professor at Saint Louis University School of Medicine, the case pushed to an extreme a challenge familiar across complex brain and spine surgery: How do surgeons prepare for anatomy they may encounter only once, and what happens when even the best technology cannot tell them what to do next?
Her team used CT, MRI, angiography and 3D models. They studied the literature and drew on the experience of a senior colleague who had participated in a similar case decades earlier.
They prepared until the unfamiliar anatomy became familiar. Then they reached what the scans could not show.
“There’s still a significant role for the human element,” Dr. Kemp told Becker’s. “We still need our hands and our minds in there.”
How to rehearse an operation that almost never happens
Craniopagus twins occur in roughly one in 2.5 million live births, according to information cited by Cardinal Glennon. Among 69 well-documented cases, only 62 separation attempts had been made worldwide, the hospital said.
That leaves surgeons without one of medicine’s most valuable teachers: repetition.
But unfamiliar anatomy itself was not foreign to Dr. Kemp. Neurosurgeons routinely encounter structures displaced or distorted by tumors and other conditions. The anatomy changes from case to case, but the fundamentals used to navigate it do not.
What changed here was the scale. The team reviewed published literature for lessons from previous separations and relied on the same principles of anatomy and surgical technique used in other complex neurosurgical cases.
They also had an unusual resource close to home. One of Dr. Kemp’s senior colleagues at Saint Louis University had participated in a separation involving partially conjoined twins in the 1980s and shared lessons from that experience.
Technology allowed the team to go further. CT scans, MRIs and angiograms were used to create 3D models of the twins’ anatomy. Pediatric radiologists, neurointerventionalists and specialists in the 3D-printing lab helped surgeons analyze and interpret the structures they would encounter.
Dr. Kemp and her colleagues studied them repeatedly.
“We knew what we would encounter during each vascular separation surgery and, ultimately, the final separation,” she said.
The goal was to make an operation few surgeons ever perform as familiar as possible before entering the OR. But there were things no model could resolve.
Where the map runs out
During the final separation, surgeons encountered small central blood vessels and connections that had not been visible in sufficient detail on the scans.
At that point, preparation gave way to judgment. The team still had tools. Surgeons used navigation, their models and intraoperative Doppler to better understand what they were seeing, including whether vessels were arterial or venous and where they appeared to lead.
The underlying decisions were not entirely unfamiliar. Dr. Kemp compared them with decisions neurosurgeons make around brain tumors: Is a vessel feeding the tumor, or does it continue beyond it to healthy brain tissue?
Similar uncertainty can arise across complex neurosurgery when tumors, congenital conditions or other pathology distort normal anatomy. The specifics may be different in a brain or spine operation, but the process is familiar: Surgeons gather as much information as possible, then reach a point where their training and judgment have to take over.
“Once we’ve gathered all the information we can, we have to make a decision,” Dr. Kemp said. “You have to decide that this is the move you need to make.”
That boundary matters as increasingly sophisticated technology enters the OR. Advanced imaging and modeling can reveal anatomy surgeons once could not see before an operation. Navigation can help surgeons orient themselves within it. But those tools cannot account for every structure or every decision.
In the twins’ case, some vessels and connections remained below the resolution of the scans. Those decisions had to be made “in the moment,” Dr. Kemp said, based on the team’s training and experience.
Even then, certainty sometimes had to wait.
“There’s always a moment while we’re waiting for the anesthesia to come off,” she said. Surgeons can know what they saw, what they decided and why. They still have to wait for the patient to awaken.
One vessel changed the plan
Not every surprise came during the final separation. The twins underwent staged vascular procedures beforehand. After the first vascular disconnection, the team began seeing an unexpected problem.
Separating a single vessel altered the balance of blood flow between the twins enough that they began developing twin-to-twin transfusion syndrome, Dr. Kemp said. One twin showed a degree of heart failure and the other a degree of renal failure.
A surgical roadmap that had taken months to build suddenly had to change.
Nephrologists, anesthesiologists, pediatricians, radiologists and other specialists had to reassess the twins’ care. The team moved up the second procedure, which Dr. Kemp said corrected the problem once the blood flow was rebalanced.
The complication exposed something the anatomical models could not predict: how the twins’ physiology would respond when one piece of their shared circulation changed.
It also gave Dr. Kemp one of her clearest lessons from the case.
“There’s never too much communication,” she said. “Everyone needs to be updated, both in writing and verbally, so the entire team is on the same page.”
The lesson was not technological. It was organizational. When one unexpected development could change the work of dozens of clinicians across specialties, communication became part of the surgical infrastructure.
Building the playbook they didn’t have
Dr. Kemp does not know whether she will ever separate another set of craniopagus twins. That makes documenting this one consequential.
Previous cases gave her team valuable information, but some of the practical details were difficult to find. Dr. Kemp pointed to questions as specific as how to position conjoined patients for an angiogram and which imaging sequences were most useful for creating 3D models.
Her team plans to publish what it learned. Dr. Kemp is careful not to characterize all of its techniques as new. Other teams around the world have used similar approaches, and her team benefited from the work that came before it.
What was missing was a more detailed roadmap.
“When teams are planning a case like this, it shouldn’t be a mystery or require them to reinvent the wheel,” she said.
That may be the paradox of operating on something so rare. Much of surgery advances through repetition. Surgeons perform an operation, refine it and pass what they learn to the next generation.
Complex neurosurgery does not always offer that luxury. Whether surgeons are confronting an extraordinarily rare condition or unfamiliar anatomy in a difficult brain or spine case, there can be moments no model can fully rehearse.
For those cases, progress depends on preserving experience another way: studying what previous teams learned, documenting what they did not and leaving the next surgeons with a better map.
Dr. Kemp’s team spent nearly a year building one for an operation they might perform only once. Now, part of the work is making sure the next team does not have to start from the same place.
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