Radiosurgery for Cerebral Arteriovenous Malformations

Abstract

Arteriovenous malformations (AVMs) are the most common intracranial vascular malformation that we encounter in our clinical practice. Patientsmay present with either headaches, seizures, or bleed. There are several classification systems described in literature to aid in management. Most of them look into the size of the nidus and the status of the draining veins. Any nidus which is compact, superficial, and in a surgically safe area are offered surgery. Most of the other AVMs aremanaged by radiosurgery or embolization either as a single treatment modality or in combination. The largest series of 258 cases with histopathology of the vascular malformations including AVMs were studied in detail and published by Karanth et al.1 It is well documented that AVMs form a conglomerate of arteries, veins, and arterialized veins. The vessel wall has varying degree of hyalinization and calcification with the intervening parenchyma showing gliotic changes and signs of hemosiderin and inflammation. This issue of the journal has interesting read on AVM. Hunugundmath et al2 documented the outcome of linear accelerator (LINAC)-based single fraction radiosurgery of AVMs on 35 patients with a median follow-up of 7 years. The median modified AVM score was 1.47. Nearly 40% of the patients had undergone embolization pre-radiosurgery. Obliteration rate observed was around 71%, and 6% of the patients had bleed post-radiosurgery. At our institute we use gamma knife radiosurgery (GKRS) for appropriate sized AVMs since 1997. The new Gamma knife ICON model enables us to use frameless stereotactic radiosurgery for indicated cases. The protocol is similar to what authors have described in their paper for LINAC, but it is a daycare procedure. The patient comes on the day of GKRS and undergoes contrast-enhanced magnetic resonance imaging (MRI) brain along with time of flight sequence imaging of brain and digital subtraction angiography (DSA). The planning is done on the GammaPlan software. The most crucial part of the planning, I believe, is delineating the nidus. We generally prefer to deliver 22 Gy (18–25 Gy) to the nidus. We may opt for volume staging or dose staging of the nidus depending on the volume and location and both have shown good results. The single fraction definitely gives a better result but may be associatedwith radiation-induced changes (RICs) depending on the nidus angio-architectural complexity. The patients are called for follow-up MRI brain annually for the first 2 years and then once in 2 years. The follow-up DSA is done in the 4th year of treatment. DSA is essential in case MRI shows residual nidus but may not necessarily be donewhenMRI reveals complete obliteration. It is good to see that in their series the authors observed only three patients developing transient neurological deficits and no mortality. I would like to remind my authors that at times radiation complications can be life threatening. The RICs usually sets in first 6 months and may be clinically symptomatic in some (►Fig. 1). Most of the time it presents as radiation necrosis, in few cases we have seen malignant edema as well. The first line of treatment is steroids which we give in tapering dose along with some cerebral decongestants. We have also tried injection bevacizumab for some of our patients and most of them have done well but some refractory edemas have to be subjected to decompressive craniectomy. Papers suggesting the role of biomarkers in early identification of patients likely to develop RIC are also there in literature. The obliteration rates are more or less the same irrespective of the radiosurgery system used. In our previous series we have shown 69% obliteration rates with GKRS.3 These residuals are usually out of field nidus and suggests hidden areas because of dilated veins. For the patients with residual nidus, we offer them repeat GKRS and the results are good. Paper by Baek et al4 covers another crucial factor that we look at when deciding the line of treatment of these AVMs. The intraand peri-nidal aneurysms associated with AVMs may prompt us to go for embolization prior to radiosurgery. The authors have described six patients with four intranidal and two peri-nidal aneurysms. Only one of them underwent