The Spetzler—Martin grading system39 has become widely accepted as an accurate method to predict patient outcomes after resection of AVMs. Composed of three components (AVM size, location [eloquence of adjacent brain], and pattern of venous drainage), this system has been validated prospectively11 and by personnel at numerous cerebrovascular centers of excellence.13,24,25,35 Although some authors have noted discrepancies between the Spetzler—Martin AVM grade and patient outcomes, especially with regard to Grade III AVMs,3,24 the general consensus supports this grading scale as practical and reliable. Unfortunately, this grading scale does not seem to correlate with successful AVM radiosurgery.22,28 This should not be surprising because the Spetzler—Martin grading system is insensitive to important factors such as AVM volume and specific location. For example, a 1-cm diameter lesion has an approximate volume of 0.6 cm3, whereas a 3-cm diameter lesion has an approximate volume of 14 cm3; the expected obliteration rates for these AVMs should be 85 to 95% and 40 to 50%, respectively.7,9,16,37 Nevertheless, both AVMs would be considered small (< 3 cm) according to the Spetzler—Martin system. Similarly, deep structures (thalamus, basal ganglia, or brainstem) and critical cortical areas are both considered eloquent brain regions; however, radiation-related complications are more likely to occur in patients with deeply located AVMs than in those harboring hemispheric malformations.6,19 Consequently, a valid instrument capable of the accurate prediction of outcomes after AVM radiosurgery is necessary to compare adequately the expected results of microsurgery and radiosurgery for individual patients with AVMs.
Successful AVM radiosurgery results in complete nidus obliteration without new or worsened neurological deficits. Karlsson, et al.,16 posited the K index as a method to predict obliteration after AVM radiosurgery. In a similar fashion, Schwartz, et al.,37 proposed the OPI as a means to estimate the chance of AVM obliteration for individual patients. Although both correlate with AVM elimination, neither index takes into account the likelihood of producing radiationrelated complications for a given radiation dose. Also, the K index and the OPI are based on the radiation dosimetry used (that is, the dose delivered to the AVM margin) at the time of treatment and not on patient and AVM characteristics alone. In this study, we propose a system that can be used to account for these shortcomings and to predict the chance of successful, single-session AVM radiosurgery, based solely on patient and AVM variables.
The authors are indebted to Drs. L. Dade Lunsford, Robert J. Coffey, and Douglas Kondziolka for their direction and for permitting their patients to be included in this study. The following physicians also contributed patients to this project and should be recognized: Drs. Dudley H. Davis, Patrick J. Kelly, Robert L. Foote, Paula J. Schomberg, Scott L. Stafford, Edward G. Shaw, and John D. Earle. Last, David J. Bissonette, P.A., M.B.A., and Deborah A. Gorman, R.N. maintained the computer databases, thus making this study possible.
Flickinger JC: An integrated logistic formula and prediction of complications from radiosurgery. Int J Radiat Oncol Biol Phys 17:879–8851989Flickinger JC: An integrated logistic formula and prediction of complications from radiosurgery. Int J Radiat Oncol Biol Phys 17:
Flickinger JCKondziolka DLunsford LDet al: Development of a model to predict permanent symptomatic postradiosurgery injury for arteriovenous malformation patients. Arteriovenous Malformation Radiosurgery Study Group. Int J Radiat Oncol Biol Phys 46:1143–11482000Int J Radiat Oncol Biol Phys 46: