A review of nearly 250 procedures challenges long-held surgical dogma and gives surgeons more flexibility to choose the best path for each patient.
For decades, neurosurgeons have followed an unwritten rule: when you can, enter the brain from the right. A new study from Weill Cornell Medicine's Department of Neurological Surgery suggests that for endoscopic surgery, that rule may necessitate modification.
Published in Acta Neurochirurgica, the study reviewed 249 consecutive ventriculoscopic procedures performed by Dr. Mark Souweidane between 2012 and 2024. It found that surgery performed through the left side of the brain was just as safe and effective as surgery performed through the right in carefully selected patients.
"We reviewed our experience with endoscopy to answer a simple question," said Dr. Umberto Tosi, neurosurgery resident at Weill Cornell Medicine and co-first author of the study. "Is endoscopy done from the left side safe?"
Why the left side matters
In most people, the left hemisphere of the brain is dominant, home to language and many other higher cognitive functions. That's why surgeons have traditionally favored the right side.
"Language is localized on the left, and a lot of higher cognitive functions localize on the left side," Dr. Tosi explained. "So if you intervene from the left side, in theory you carry the risk of injuring those functions."
However, endoscopic surgery is different from traditional open surgery. Surgeons work through a small tube with a camera and specialized instruments, reaching the brain's fluid-filled cavities, called ventricles, with minimal disruption to surrounding tissue.
"Endoscopy is done through a much smaller working channel that allows you to minimize brain injury," Dr. Tosi said. "The pathway you go through is smaller, which provides more control when it comes to preserving function."
What the team found
The researchers compared 68 left-sided procedures with 181 right-sided procedures. These included endoscopic third ventriculostomies (ETVs) to treat hydrocephalus, colloid cyst resections, tumor biopsies and tumor resections within the ventricles.
"To give you a very short answer, the answer is yes," Dr. Tosi said. "In our hands, going from the left is no riskier than going from the right."
The results were striking. The surgical goal was achieved in every left-sided procedure. Complication rates were low for both groups: 2.9% for left-sided surgery and 3.9% for right-sided surgery. Nearly all patients in both groups returned to work or school after surgery. For ETV procedures, success rates on both sides were in line with those predicted by a standard scoring system.
Left-sided surgery was chosen for specific anatomical reasons, such as a tumor or cyst positioned toward the left, a larger left ventricle or opening, or blood vessels blocking access on the right.
"Surgical dogma before would dictate to go from the right and struggle more with the approach," Dr. Tosi said. "In our case, going from the left allowed us to achieve our surgical goal with less difficulty." Dr. Tosi added an important caveat: these results reflect surgery performed by expert endoscopists at a high-volume center.
What this means for patients
For patients facing endoscopic brain surgery, the takeaway is reassuring. Our results justify a different prioritization, that balances optimizing the intended surgical goal with safety. If their surgeon recommends a left-sided approach, it's because that approach offers the best access to the problem, and the study shows it carries no added risk.
A resident's perspective
For Dr. Tosi, who plans to become a brain tumor surgeon with neuroendoscopy as a core part of his practice, the project was a chance to put data behind clinical experience.
He also pointed to the training opportunities that make this kind of work possible. "At Weill Cornell Medicine, we have the privilege of having one of the largest endoscopic cohorts," he said. "Our experience, especially from a residency training perspective, is unparalleled."
The study, "Ventriculoscopic outcomes from 249 consecutive patients: the role of a left sided approach," was authored by Dr. Umberto Tosi, Dr. Patrick J. Halloran, Dr. Gary Kocharian, Dr. Heidi Allison Bender and Dr. Mark M. Souweidane. Read the full study.