Re: How is it possible to do brain surgery without brain impairment?

Dear Michael,

I'm very glad that everything has turned out well for your friends. The fact is, many people who have tumors removed do have problems after their surgery, despite their doctor's best efforts. Sometimes tumors are just in a difficult location, and can only be removed by also removing normal brain tissue. However, neurosurgeons go to great lengths to minimize the risks.

The goal the surgeon is to remove as much of the tumor as possible without creating new deficits for the patient. One key to doing this is precisely localizing the tumor. Precise localization allows the surgeon to more completely remove the tumor and helps to determine an approach to the tumor which will minimize damage to normal brain.

Initially, a tumor can be localized by the type of symptoms it produces. Tumors will disrupt the activity in and around the area in which they grow. A neurologist or neurosurgeon can compare the symptoms with the known function of different brain areas and get a good idea of the general location of the tumor.

After the neurosurgeon has an idea of what kind of tumor might be causing the problem and its general location, he will use imaging technology to pinpoint it. Imaging technology has advanced rapidly in the past few years. Now, much of neurosurgery is done using magnetic resonance images of the brain. An MRI scan can produce a very detailed view of brain anatomy, and can distinguish between normal brain tissue and the tumor. Several MRI images can be used to make a map of the person's brain, and very precisely define the location of the tumor. There are a few hospitals which currently are capable of making MRI images during the surgery. In this way the surgeon can take out the tumor, then immediately do a MRI and see if any was missed. He can then remove any left over portions.

Depending on the location of the tumor, the neurosurgeon may have to determine the location of the "eloquent" portions of the brain. The "eloquent" brain is, broadly speaking, those portions of the brain from which responses can be evoked by electrical stimulation. Another, even broader, but perhaps more appropriate defintion, is that the "eloquent" brain is those parts which allow a person move around, see, hear, speak and understand language, use objects and remember.

Knowledge of brain organization can go a long way toward identifying which areas are "off limits". In my personal research, I have found I can pretty accurately identify specific portions of a monkey's brain related to arm movements just by looking at the brain surface. However human brains are certainly more complex, and the exact location of the critical areas varies a little from person to person. Neurosurgeons use a variety of methods to determine exactly where they are. Perhaps the most widely used and most accurate way of determining the location of the "eloquent" cortex is by doing electrical mapping during the surgery.

This mapping is generally done while the person is awake. The surgeon will use a small electrode to stimulate different parts of the brain, and look for a response. Each stimulated location is marked, and by stimulating several locations, the surgeon can construct a map. To test for areas related to speech, the surgeon will have the patient speak while he stimulates. If their speech stops when the current is turned on, then that area needs to be left alone.

After the location of the tumor and the location of the "eloquent" cortex has been determined, the surgeon will remove the tumor. In some cases the tumor is buried deep in the brain, or is located under a particularly important portion of the brain. Here, the knowledge and experience of the surgeon becomes crucial. He will have to determine the path to the tumor which will cause the least amount of damage. He will have to rely on his knowledge of brain anatomy, his sense of the 3 dimensional location of the tumor and his knowledge of the pathways that connect different parts of the brain. When it comes right down to it, even with the help of the best pictures in the world, the surgeon has to be able to recognize the tumor with his own eyes, and be able to visually recognize those portions of the brain which can and can not be safely cut.

If you have any questions or comments, or would like a list of some of the references I used to construct this answer, please send me an email.