Abstract
Six patients with medium-sized arteriovenous malformation (AVMs, 3.0-6.0 cm in maximum diameter), treated by gamma knife radiosurgery without preceding embolization, are reported. The AVM manifested with intracranial hemorrhage in three cases and with seizure in the other three. The maximum nidus diameter ranged from 3.4 cm to 5.7 cm, with a mean and a median of 4.0 cm and 4.1 cm, respectively. Although total AVM coverage at the time of dose planning was feasible in four patients, the selected dose at the periphery of the nidus was limited to 7.2-14.0 Gy (total coverage and non-optimal dose treatment). The two remaining patients had only partial coverage; the part of the nidus adjacent to the major feeding artery was covered and a dose of 21.0-25.0 Gy was given within this limited area, although the remaining part of the nidus was irradiated with a dose of 5.0-7.0 Gy or less (partial coverage and optimal dose treatment). Neither hemorrhage nor significant radiation-induced complications occurred in any of the six cases during the postradiosurgical follow-up period which ranged from 18 to 85 months (mean 48 months). Complete nidus obliteration was angiographically confirmed 38 months after radiosurgery in one case, more than 90% obliteration of the treated nidus, respectively, 36 and 70 months after radiosurgery, in two cases. Magnetic resonance (MR) angiography demonstrated disappearance of the nidus in one case and remarkably decreased nidus volume in one, respectively, 30 and 18 months after radiosurgery. In the one remaining case, MR imaging obtained at 24 months after treatment showed a significantly diminished flow signal void, as well as the appearance of a gadolinium enhanced area within the treated nidus. In addition, a T2-weighted image showed hyperintense edema surrounding the AVM. These results indicate that single irradiation of a medium-sized AVM using a gamma knife, though not optimal, can produce complete nidus obliteration, or significant nidus shrinkage, for two-six years, or more, after radiosurgery. Even in the latter instance, the shrunken AVM can easily be re-treated using a gamma knife.
