Microsurgery of skull base tumors is a technologically intensive endeavor. A high-power microscope with a stable, anti-vibratory base mount is important for proper visualization of vital structures. A high powered drill with a wide assortment of burrs is essential, as it is critically important to be able to navigate around each nerve and blood vessel. Delicate microsurgical instruments in a wide variety of sizes and angles, such as hooks, scoops, scissors, and probes, are required. These permit atraumatic microdissection of the tumor off the vital structures.
Cranial nerve monitoring is often used in skull base surgery. A neurophysiologist is present in the operating room throughout the surgery, and tracks the various nerves' health on a computer system. This optimizes the preservation of cranial nerves by facilitating gentle microdissection of the tumor off of the nerve.
A three-dimensional image guidance navigation system may be required for large tumors that envelop major vascular or neurologic structures. This computer system is programmed to project images of an individual patient’s tumor on a TV for use in the operating room. Using a probe referenced to the patient on the operating table, the surgeon can verify exactly where each vital structure is in relation to the tumor.
What is the success rate of skull base surgery and what other treatment options are available besides surgery?
The goal when managing skull base tumors is to improve patient survival and quality-of-life. Obviously, the best way to treat a skull base tumor is a decision that can only be made after close collaboration between the patient and the physician team. Proper patient selection is critical to good outcomes.
Not all skull base tumors require intervention. Some are so slow growing that they pose only minor risk of more serious problems, especially to older individuals. In such cases, the tumor may simply be monitored by periodic imaging studies. In this situation, because the tumor is predicted not to grow to a size where it will cause disabling symptoms prior to the patient dying of other reasons. Thus, these patients can be treated with the philosophy that they will “take the tumor with them”.
Another treatment option that is at times preferable to microsurgery in selected skull base tumors is stereotactic radiation. The goal is to use a computer-guided delivery system to focus the radiation directly on the skull base tumor, while minimizing radiation exposure to the sensitive surrounding structures. While this technique does not remove the tumor, it can reduce or stop the tumor growth in certain situations. There are several different brands of devices that can deliver radiation in a stereotactic fashion, including Gamma Knife, Novalis, Cyberknife, and proton beam. While there are some important differences between them, the ultimate results for many types of tumors are quite similar. That is, the tumor is irradiated and the surrounding normal tissue receives a substantially lower dosage. The Cyberknife was developed at Stanford and we have found it to be a very successful treatment option for skull base tumors.
Success rates of skull base surgery have continued to improve. This is because of the evolution of modern approaches designed to reduce the requirement of brain retraction and sacrifice of normal structures in order to get to the tumor. Our surgical philosophy is based on the concept of removing as much tumor as possible, while maintaining preservation of function. This has led to excellent rates of tumor control, long-term patient survival, as well as in numerous, important quality-of-life measures.