deficits or worsening of pre-operative deficits was 27.4% - a figure many times that of gamma-knife-treated patients.

Unfortunately, not all AVMs are ideal or indeed suitable for elective surgery. The resulting problems are incomplete resection and surgical complications. Those with higher Spetzler-Martin grade have a higher neuro-surgical risk and surgery has to be more cautious. This leads to not infrequent post-surgical remnants, particularly with AVMs located in the thalamus, basal ganglia and brainstem [4]. Despite the negative reporting bias, the evidence is clear that surgery for these deeply placed AVMs carries a high surgical risk [5].

Endovascular techniques are increasingly used for cerebral AVMs. Analysis of the technique and role of interventional radiology is beyond the scope of this chapter. Suffice it to say that a close cooperation with one's neuroradiologist is an essential factor in the successful management of AVMs.

Since the early reports by Steiner et al. [6], describing successful obliteration of AVMs by radiosurgery, many hundreds of abstracts of proceedings, papers and book chapters have appeared to prove the same [7, 8, 9]. Concerning the mechanism, the main effect of radiation is upon the endothelial cells within the nidus, with an additional effect of myofibroblast development in the connective tissue stroma [10].

It is broadly accepted that about 80-90% of AVMs undergo thrombo-obliteration after single-dose radiation (Fig. 8.1). The efficacy depends on the radiation dose given to the periphery of the lesion. In small (<1cm3) lesions, this dose is usually 25 Gy, which can achieve close to 100% obliteration rate [11]. In cases of larger AVMs, the dose is kept lower in order to keep complications to around 5%. Series with a significant component of large malformations and utilizing lower doses have lower response rate, but even in those the success rate is around 65-75% [12]. It has to be emphasized that these series largely consist of patients referred for radiosurgery because the surgeon in charge of the patient considered open surgery to be of too high risk, usually owing to the eloquent position of the nidus ("inoperable").

The response shows a latency of 1-3 years, with only minor changes occurring in the third year. The risk of hemorrhage appears to decline

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