One of the biggest advances in neurosurgery over the past decade has been the development of endoscopic techniques for treating tumors in the skull base and brain. Lesions that formerly required craniotomy and brain retraction are now being accessed directly via natural pathways through the nose and sinuses. All three Mayo Clinic campuses have surgeons who are experienced with these endoscopic techniques and are using them in an increasing number of cases.
"All of our pituitary adenomas are now treated endoscopically. We are able to visualize areas of the sella we couldn't see before, which makes a complete resection more likely," says Naresh P. Patel, M.D., a neurosurgeon at Mayo Clinic in Arizona.
Other tumors treated endoscopically at Mayo include meningiomas, clival chordomas, nasal tumors, chondrosarcomas and craniopharyngiomas, as well as lymphomas and melanomas. "Endoscopic surgery, especially for extradural central skull base tumors, has essentially replaced or eliminated some of the very extensive and at times disfiguring transfacial approaches previously necessary," says Michael J. Link, M.D., a neurosurgeon at Mayo Clinic in Rochester, Minn.
A specialized skull base team comprising a neurosurgeon and an otolaryngologist work together during endoscopic procedures, supported by neuroradiologists and interventional neuroradiologists. "That combined expertise is necessary to offer our patients the best possible results in terms of reducing morbidities as well as optimizing the outcome from the operation," says Devyani Lal, M.D., an otolaryngologist and endoscopic skull base surgeon at Mayo in Arizona.
The proximity of certain skull base tumors to vital neurovascular structures increases the risk of morbidities arising from surgical removal. Although microscopic surgery has been the gold standard, for certain skull base lesions an endoscopic approach is less invasive and offers important advantages, particularly in visualizing tumors.
Unlike the microscope, which focuses light narrowly on the tumor, the endoscope works more like a flashlight, focusing light outward. "With the microscope, it's like looking through a keyhole in a door. You have a very narrow, straight-on view," says Rabih G. Tawk, M.D., a neurosurgeon at Mayo Clinic in Jacksonville, Fla. "The endoscope brings your eye right next to the tumor."
Various endoscopes offer differing angles of vision, which is particularly helpful for resection of hormone-secreting pituitary tumors. "Achieving remission requires removing the hormone-secreting portion of the tumor, which may be hidden somewhere in a corner of the sella," Dr. Patel notes. "Sometimes, we can angle a microscope a bit to see more superiorly or inferiorly, but it's very difficult to see farther off to the left or the right. The endoscope actually can be advanced into the sella after some of the tumor has been removed. The visualization is incredible."
Endoscopic surgery also can be used to treat tumors, such as esthesioneuroblastoma, that extend to the anterior skull base. "With the endoscope you can look up toward the skull base and resect the bone, the tumor and the dura — which can be invaded by tumor — and even take out tumor that's abutting the brain," Dr. Patel says.
The endoscope can also provide visualization downward into the spine, giving surgeons access to lesions of the clivus and C1 or C2 areas. Another advantage is that it can help the surgeon find and repair a CSF leak, which can occur after removal of a large skull base tumor.
A number of technological advances have enhanced endoscopic surgery techniques:
"We can now accurately know our proximity to adjacent structures beyond our visible fields," Dr. Tawk says. "The use of intraoperative CT and MRI also provides great feedback while the patient is still undergoing surgery."
This enhanced visualization and access to tumors can provide oncologically sound resection with negative margins while avoiding a large open craniotomy and brain retraction. "The endoscopic approach does not compromise oncologic resection for decreased morbidity and cosmesis," Dr. Lal says. She notes that early results from multiple centers are encouraging, although long-term follow-up data are awaited.
Unlike the microscope, most endoscopes provide only a 2-D view, although 3-D endoscopes are being developed. "You lose depth perception, so there is a learning curve associated with endoscopic skull base surgery," Dr. Tawk says. "But once you acquire experience, you can overcome this limitation."
Mayo in Arizona offers an annual course in endoscopic sinus and skull base surgery. Guided by international faculty, participants learn endonasal surgery techniques and practice in a cadaver laboratory. Dr. Lal directs the four-day course. "Once a neurosurgeon sees that endoscopic view, it's very difficult to go back to the microscope," she says. "With the endoscope you do a better resection, and your postoperative reconstruction work is much tighter. That panoramic view really affects the results you obtain from resection of these tumors."