To Adam Mamelak, MD, the traditional method of skull base tumor removal is "like trying to change the muffler at the bottom of your car by opening up the hood of the engine and going around the entire engine block."

Rather than operating at the skull base via an invasive craniotomy, Mamelak and the expert neurosurgery team at Cedars-Sinai are leading the way on innovative methods to resect a skull base tumor from underneath the brain, using an endonasal approach and minimally invasive endoscopic methods.

"This is going to revolutionize this area of skull base surgery for tumors that were traditionally always operated on through a craniotomy," Mamelak said. "The difficulty is, there’s a relatively small subset of surgeons that are experts at these procedures."

The skull base is a complex area that sits at the interface between the face, brain and skull, and contains vital arteries and veins connecting the brain to the body. Tumors that affect this area include pituitary tumors, meningiomas, craniopharyngioma, chordomas and chondrosarcomas.

With the endoscopic approach, the surgeon enters through the nose, avoiding the need to open the skull, manipulate the brain and navigate around critical blood vessels and the sensitive optic structures.

"As the technology and instruments have expanded, the surgeon can now go truly inside the brain from underneath it, rather than on top of it," Mamelak said.

Advanced endoscopic tools can maneuver and angle in many directions, providing a wider navigable field of vision inside of the skull. The surgeon carefully removes bone and tissue at the base of the skull and behind the back of the nose to expose and ultimately resect the tumor. Otorhinolaryngologists (ear, nose and throat surgeons) work with the neurosurgeons as a team and play a primary role in gaining access to the skull base and repairing it after the tumor has been removed. 

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Transsphenoidal endonasal endoscopic surgical procedures offer four advantages: improved field of vision for the surgeon; the ability to work below and easily see critical structures such as the optic nerves and carotid arteries rather than around them; avoiding the need for a craniotomy; and eliminating cosmetic impacts for the patient.

"Cosmetically, it looks literally like no surgery was done," Mamelak said. "There is no external swelling or bruising."

Most importantly, he added, the technique is effective. New data shows that for some skull base tumors, the endoscopic approach is associated with better patient outcomes.

Due to the novel nature of the procedure, data is limited, with studies typically occurring at a single institution. A 2018 meta-analysis in Neurosurgery that included Cedars-Sinai analyzed the outcomes of tuberculum sellae meningioma resection, comparing the traditional transcranial approach to an endonasal endoscopic approach. The study found "no differences in rate of gross total resection or perioperative complications between the two groups." The endonasal endoscopic group was associated with higher rates of cerebrospinal fluid leak, but increased postoperative visual improvement.

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These procedures are not widely available because of the difficulty of developing the surgical skills and expertise.

"To get good at this approach, you have to do a lot of pituitary surgery to understand the basics really well," Mamelak said. "Then you have to get comfortable with removing more and more bone and tissue, and working in a way that is sort of counterintuitive."

Mamelak said the immediate hurdle to advancing innovation in minimally invasive surgical removal of skull base tumors is getting surgeons on board. Many times, Mamelak sees other surgeons opt for the craniotomy route they are more comfortable with—even when patients may be strong candidates for operating through the nose.

"It is difficult to convince surgeons to stop doing more traditional procedures and pursue a new, better option," he said.

Over time, as data accumulates and surgeons build familiarity and skill with the procedure, he believes more surgeons will increasingly utilize the endoscopic procedure. At a minimum, he hopes to begin to see more surgeons refer patients who may be good candidates for endoscopic tumor removal for a consultation.

"If you have the expertise, the experience, the knowledge and the team put together, it’s tremendously revolutionary and can offer great benefits to patients," Mamelak said.

For surgeons striving to become expert in the new method, the endoscopic endonasal approach can be practiced in an extremely lifelike environment. A video recently published in Operative Neurosurgery shows the utility of preoperative planning and surgical rehearsal in virtual reality. Surgeons can create three-dimensional renderings to examine the anatomy, then choose and rehearse the surgical approach. Rehearsal can improve surgical efficiency and has the potential to shorten the length of the surgery.

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Mamelak is excited for what’s next in endoscopic tumor surgery. In the future, he envisions an opportunity for flexible scopes and instruments and even robotic manipulations where a robotic tool can visualize or be used for dissection.