From OncoLog, November-December 2010, Vol. 55, Nos. 11-12
Endoscopic Surgery for Skull Base Tumors
By Bryan Tutt
Surgery for skull base tumors results in a cure for many patients. For most of these patients, traditional open craniofacial surgery is the safest approach with the best chance of success. In recent years, however, endoscopy-assisted surgery, which leaves no visible scars, has been found to be effective for the resection of some skull base tumors.
Benign or malignant tumors of various types—including squamous cell carcinoma, melanoma, adenocarcinoma, sarcoma, olfactory neuroblastoma, and others—may originate from or extend into the skull base. Chemotherapy and/or radiation can be used to effectively treat some malignant skull base tumors, and many benign skull base tumors require observation only. However, most malignant skull base tumors and any benign tumors that threaten vital structures must be removed surgically.
Traditional open surgery for skull base tumors may require facial and scalp incisions and movement of the facial bones or part of the cranium. In contrast, during endoscopy-assisted surgery, the endoscope and surgical instruments are inserted through the nose and approach the skull base tumor from below, without the need for incisions.
The endoscopic procedure
When surgeons prepare for an endoscopic procedure, they also make a plan for an open procedure to be used if tumor-free margins or adequate skull base reconstruction cannot be achieved using the endoscopic procedure. “We always tell the patient that we will be ready to switch to open surgery and use time-honored surgical techniques if endoscopic surgery is not able to achieve the ultimate goal, which is to cure the patient of his or her cancer,” explained Ehab Hanna, M.D., a professor in the Department of Head and Neck Surgery at MD Anderson Cancer Center.
In the operating room, images obtained earlier by computed tomography or magnetic resonance imaging are loaded into a computer-based image guidance system. Surgeons use an infrared sensor to point to anatomic landmarks, such as the nose or right eye, on both the patient and the image. The image guidance system then correlates these locations on the image, or map, to be displayed during surgery. “During surgery, this is used to query and find our exact location, much like a surgical GPS,” Dr. Hanna said.
The surgeons begin the procedure by introducing the endoscope through a natural opening, usually a nostril. This allows access to the skull base without retracting critical structures such as the brain. For tumor resection, various instruments can be introduced alongside the endoscope. For example, surgeons may use a highspeed debrider, adapted from arthroscopic technology, to debulk the tumor and to expose the tumor’s point of attachment. One surgeon uses the instruments while the other manipulates the endoscope to ensure adequate visualization.
The roles of the neurosurgeon and the head and neck surgeon are complementary. “When the tumor is in the intracranial cavity, it is primarily the neurosurgeon operating and the head and neck surgeon providing the view with the endoscope,” said Nicholas Levine, M.D., an assistant professor in the Department of Neurosurgery. “But when the tumor is primarily in the sinus, the neurosurgeon may use the endoscope, freeing the head and neck surgeon’s hands to operate the instruments.”
“It’s important that the neurosurgeon and I are on the same page,” added Michael Kupferman, M.D., an assistant professor in the Department of Head and Neck Surgery. “If the neurosurgeon is resecting the tumor, I have to know where he’s going so I can provide proper visualization to facilitate the resection.”
Once the surgeons are satisfied that they have removed the tumor with clear margins, tissue grafts harvested from other parts of the patient’s body are used for a multilayered reconstruction of the skull base. The tissues are packed into place and held together with tissue glue. The inability to suture the dural membrane is an important limitation of the endoscopic approach, and as a result, the approach’s most common complication is spinal fluid leakage, which carries the risk of meningitis.
To minimize the risk of spinal fluid leakage, the patient may be kept on bed rest for 1–2 days following surgery. A typical hospital stay for a patient after an endoscopic procedure is 2–3 days.
Although the number and types of tumors that can be removed using the endoscopic approach have increased dramatically over the past decade, less than half of skull base tumor resections can be performed using the endoscopic approach.
“The key to success in endoscopic surgery is selecting it for the right patient,” said Dr. Hanna. The choice of surgical technique is determined by the ability to meet the primary treatment goals—negative surgical margins, protection of critical neurovascular structures, and reconstruction of the skull base. Patients with tumors that invade the skull base without massive invasion of the brain are the best suited candidates for the endoscopic approach.
“Usually, if a tumor can be approached endoscopically, it can also be approached though an open procedure,” Dr. Levine said. “In that case, the choice of surgical approach is largely a matter of which procedure gives us better visualization. When we do an open procedure, we use an operating microscope. The microscope gives us three-dimensional visualization but less illumination than the endoscope, which is brighter but two dimensional.”
Dr. Kupferman added that the surgical microscope offers only direct line-of-sight visualization, while the endoscope allows the surgeon to see around corners.
“The critical issue is what happens at the end of the visualization path using either the microscope or the endoscope,” said Franco DeMonte, M.D., a professor in the Department of Neurosurgery. “Philosophically, it’s nice to think that it’s better to go in through the nose without making the incisions required for an open procedure. But the risk is not the incision; the risk is associated with the critical structures in the region where you’re operating.” For example, some skull base tumors cannot be removed endoscopically without destroying much of the sinus anatomy; an open procedure would result in less morbidity for patients with such tumors.
At MD Anderson Cancer Center, treatment decisions for patients with skull base tumors are made by a multidisciplinary team of surgeons, radiation oncologists, and medical oncologists who meet each week at an in-house head and neck tumor conference. “Skull base tumor pathologies are diverse,” Dr. Levine said, “and they need to be evaluated using a team approach.”
The pathologic type of the skull base tumor is the most important factor influencing treatment decisions. “There’s no cookie-cutter approach,” Dr. Hanna said. “Gamma knife, radiosurgery, proton therapy, intensity-modulated radiation therapy, chemotherapy—we have the full gamut of therapies available to complement, precede, or replace surgery.”
Another therapy that may one day be available to treat skull base tumors is robotic surgery. In 2007, surgeons at MD Anderson conducted a proof-of-concept study showing that the da Vinci Surgical System, a robotic system already in use for laparoscopic surgery, could be used for the endoscopic removal of skull base tumors. However, Dr. Hanna said that smaller, more precise instruments must be developed before the robot can be used for skull base surgery.
The da Vinci system, when and if it is ready for clinical use to treat skull base tumors, will offer three-dimensional binocular visualization and the ability to endoscopically suture the dural covering of the skull base. These advantages over existing endoscopic techniques might make endoscopic surgery an option for more patients.
The importance of careful patient selection was substantiated by a 2009 retrospective study of sinonasal and skull base malignancies removed by endoscopic surgery at MD Anderson. It was the largest U.S. study of such tumors, and the researchers found no difference in survival rates between well-selected patients whose tumors were removed endoscopically and patients who underwent craniotomy. For all patients in the study, 5-year and 10-year disease-specific survival rates were 87% and 80%, respectively.
Dr. DeMonte said the consistent survival rates reflect a commitment to using whichever technique provides the highest degree of resection.“Endoscopic surgery is an option, but it is not the only option,” Dr. Levine said. “The overall evaluation of the patient dictates the kind of treatment the patient needs.”
For more information, contact Dr. Hanna at 713-745-1815, Dr. DeMonte at 713-563-8705, Dr. Levine at 713-563-8706, or Dr. Kupferman at 713-794-1910.