Doctors often use grading scales that measure the most salient features of an illness to predict the outcome of a given treatment. These scales have been developed over the years and take in the experiences of many doctors and their patients with varying degrees of a problem. Things like how large is the injury, how old is the patient, and how have other patients in the past done with this particular treatment are taken into account.

Dr. Steven R. Isaacson from the Gamma Knife Center and Dr. E. Sander Connolly from the Cerebrovascular Center and their colleagues have given a comprehensive review of one problem in particular, Cerebral Arteriovenous Malformations (AVM).  AVM is a condition in the brain where tiny blood vessels in one area become tangled. It is commonly treated with radiosurgery, but if left untreated the AVM can cause damage to brain cells, cause a hemorrhage, or trigger seizures. Dr. Isaacson says that the aim of their paper was to give neurosurgeons the best tools out there to help them answer their patients questions about outcome.

The Gamma Knife is one of the devices used to perform radiosurgery on an AVM. This is not the kind of surgery we are used to thinking of, it doesn’t even use a knife, rather it focuses a highly concentrated beam of radiation into the brain. The results of radiosurgery can take between one and three years to fully realize but is still preferred when open brain surgery would be too risky for the patient. The aim of the surgery is complete obliteration of the AVM. That means, within the three year window, the AVM disappears and normal blood flow returns to the area.

In their paper, Drs. Isaacson and Connolly and their colleagues reviewed a number of different grading scales that have been developed to predict the outcome of radiosurgery for patients with an AVM and have come up with two in particular that are the most useful.

The first is the Spetzler-Martin (SM) grading system, proposed in 1983 to predict the success of AVM microsurgery. This system devides AVMs into six basic types using size, where in the brain it is located, and what its venous drainage is like, to predict surgical outcome. Since then a modified version of this scale (mSM) was developed to account for more complicated types of AVM. The authors say, both grading systems “are easy to use and have been shown to be relatively predictive of radiosurgcial outcome.”

The second scale they recommend is the Radiosurgery-based grading system (RBGS). The RBGS was proposed in 2002 and uses values for the volume of the AVM and it’s location in the brain, but also includes the patient’s age.

Dr. Isaacson has stressed that outcome is an important subject to discuss with patients even when they haven’t brought up the question themselves. These grading systems give doctors the tools to do just that.

To learn more see Drs. Isaacson and Connolly’s paper A Comprehensive Review of Radiosurgery for Cerebral Arteriovenous Malformations: Outcomes, Predictive Factors, and Grading Scales in Vol. 86, No. 3, 2008 of the Journal of Stereotactic and Functional Neurosurgery.