From OncoLog, November 2006, Vol. 51, No. 11

Treating Skull Base Tumors

by Sunni Hosemann

At the base of the skull lies an intricate scaffolding upon which the brain rests. As the floor of the cranium, its nooks and hollows are marked by various sized openings through which large vessels and critical nerves—including the brainstem itself—traverse on their way to and from the brain. Tumors that grow here can originate from any of the tissue types nearby, such as brain, nerve, sinus, or bone. These tumors lie deep within the head, and they can insinuate themselves in the most difficult ways—hiding in the hollows, enmeshing with tissues, and twisting themselves around critical neural and vascular structures.

Unique for their diversity as well as their location, dozens of different kinds of tumors arise in the skull base, and some are very rare. They include meningiomas, neuromas, angiomas, schwannomas, melanomas, and several kinds of carcinomas and sarcomas, as well as pituitary tumors, bony tumors, cysts, fibrous lesions, and a host of others.

Their treatment requires the expertise of many: for a start, it’s best to have surgical, medical, and radiation oncologists who specialize in these kinds of tumors. To fully optimize outcomes beyond survival, including restoration of form, function, and quality of life, the services of a host of other medical and rehabilitation specialties are necessary.

Not all skull base tumors are cancers. “At least half of the patients we see have benign tumors,” said Franco DeMonte, M.D., a co-director of the Skull Base Tumor Program at The University of Texas M. D. Anderson Cancer Center and a professor in the Department of Neurosurgery. The malignant tumors require treatment—surgery plus chemotherapy or chemoradiation given neoadjuvantly or adjuvantly.

“Usually, we can tell by imaging studies whether a tumor is benign or malignant,” said Dr. DeMonte. The malignant tumors must be biopsied: “We must have accurate pathology,” he said, “and for that we rely on neuropathologists and head and neck pathologists who are specialized in this area.” Some of the benign tumors can be left alone and serially monitored; others can grow and impinge on vital structures and must be treated.

Treatment advances

One of the most significant strides forward in skull base tumor treatment has come simply from collaboration. Disease below the skull base has traditionally been the purview of head and neck surgeons, while neurosurgeons usually dealt with everything above it. Collaboration between these two disciplines, little more than a decade old, was necessary to best treat these tumors, which occupy the border between the two. “These tumors require bi-directional access—the combined expertise of those comfortable with intracranial and extracranial approaches,” said Ehab Y. Hanna, M.D., a co-director of the Skull Base Tumor Program and a professor in the Department of Head and Neck Surgery. That collaboration has resulted in a unique subspecialty; members of The North American Skull Base Society come from both disciplines.

Surgical treatment of skull base tumors has dramatically advanced through the use of minimally invasive techniques. In the past, operating on these tumors involved major incisions and consequent facial scarring. “An extensive external approach meant a large facial incision and displacement of bone—essentially a temporary disassembly of the bony structures of the face,” said Dr. Hanna. “These operations could be extensive: 10- to 12-, even 14-hour, surgeries with prolonged hospital stays.”

Minimally invasive surgery allows access to the tumor via an endoscope through existing cavities, like the nose, significantly reducing the length of surgery and of recovery. “This factor alone translates into a better functional outcome,” said Dr. Hanna, who was recruited to the program for his rare expertise in the use of minimally invasive techniques for tumors of the skull base.

These techniques are constantly improving, meaning that more and more tumors can be approached this way. Other new technologies are emerging that also bear great promise for skull base tumor treatment.

“The da Vinci Surgical System, a new robotic surgical technology, is one of the avenues we’re interested in adapting for skull base surgeries,” said Randal Weber, M.D., professor and chair of the Department of Head and Neck Surgery. The system, currently in use in other types of surgery, will require modifications and refinements for this application. The da Vinci system has two attributes that should prove critically useful in skull base tumor surgeries: high-definition visualization and instrumentation that behaves like a super-dextrous wrist that can operate in very confined spaces. The visualization is provided by a fiberoptic stereoscopic camera system, which allows the surgeon to see the three-dimensional operative field in full color, magnified, and at very high resolution. The system’s computer translates the surgeon’s hand movements to robotic arms that operate very fine instruments. According to Dr. Hanna, “The advantage of da Vinci is that the instrument used can be very small, meaning that the size of the access can be small, and the robotic arm has free movement in all axes, allowing you to go around corners, behind vessels.”

“The BrainSUITE at M. D. Anderson is another development that will be of decided value for some of the surgical cases we see,” said Dr. Hanna. BrainSUITE’s state-of-the-art equipment gives surgeons a capability critical to removing intracranial tumors: high-intensity intraoperative magnetic resonance imaging. Skull base tumors present some of the same challenges to the surgeon that many brain tumors do: surgeons must chase the farthest reaches of the tumor, calculating how deep to go to completely resect it without damaging critical structures nearby. Without intraoperative imaging, surgeons must rely on preoperative images and their own calculations, which must also account for positional shifts that typically occur during brain surgery. “In addition, these tumors are often found in ‘corners’ and near intricate structures,” said Dr. DeMonte, “making intraoperative imaging especially useful for endoscopic procedures.”

Proton therapy, newly available at M. D. Anderson, is another new technology that is expected to benefit many patients with skull base tumors. “We expect skull base tumors to be one of its most important applications,” said Dr. DeMonte. Proton therapy is more advanced than standard radiation therapy because the exact location at which the proton beam will deposit its energy can be programmed in three dimensions, meaning that it can be aimed at deep tumors and contoured to their shape. Healthy adjacent and intervening tissues go unharmed.

This precision will be a distinct advantage with the types of tumors found in the skull base. Consider a tumor near the optic chiasm: “With surgery, we can come close to it—perhaps 2 mm—and then follow with proton therapy to perhaps destroy that remaining 2 mm. That’s not possible with conventional radiation therapy,” said Dr. Weber. Three protocols for skull base tumors are currently in development for proton therapy, targeting tumors of the sinus cavity and nasopharynx and bony tumors of the skull base.

This group of physicians believes that whether benign or malignant, rare or common, tumors are best treated in a specialized program where there is a concentration of experience, as well as rehabilitation resources for the critical path to a quality life for patients, and that just such an environment exists at M. D. Anderson. “I have never worked in a place that had this gamut of services,” Dr. DeMonte said. “This is our focus: it’s all we do.”

For more information on this topic or for questions about M. D. Anderson’s treatments, programs, or services, call askMDAnderson at (877) MDA-6789.

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