Successful gamma knife radiosurgery depends on the volume of nidus of cerebral arteriovenous malformations (AVMs). Because of lower possibility of obliteration of large AVMs treated by gamma knife radiosurgery , embolization therapies were carried out in 10 cases out of 50 AVMs to reduce the volume of nidus before gamma knife radiosurgery . The strategy is as follows: 1) when the volume of nidus is less than 5 ml , gamma knife radiosurgery is selected as the first treatment. 2) when the volume

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... f nidus is from 5 to 10 ml , embolization is recommended in selective cases in which the procedure seems to be safely performed . 3) When the volume of nidus is over 10 ml, embolization should be tried in all cases. In this strategy, it is essential to evaluate the accurate volume of nidus before gamma knife radiosurgery to decide whether embolization should be carried out or not. Angiography with painless fixation of Leksell frame was thought to be best procedure to meansure the accurate volume of nidus before gamma knife radiosurgery .