Top 25 Cited Gamma Knife® Surgery Articles - Volume 111

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Masahiro Izawa, Motohiro Hayashi, Mikhail Chernov, Koutarou Nakaya, Taku Ochiai, Noriko Murata, Yuichi Takasu, Osami Kubo, Tomokatsu Hori and Kintomo Takakura

Object. The authors analyzed of the long-term complications that occur 2 or more years after gamma knife surgery (GKS) for intracranial arteriovenous malformations (AVMs).

Methods. Patients with previously untreated intracranial AVMs that were managed by GKS and followed for at least 2 years after treatment were selected for analysis (237 cases). Complete AVM obliteration was attained in 130 cases (54.9%), and incomplete obliteration in 107 cases (45.1%). Long-term complications were observed in 22 patients (9.3%). These complications included hemorrhage (eight cases), delayed cyst formation (eight cases), increase of seizure frequency (four cases), and middle cerebral artery stenosis and increased white matter signal intensity on T2-weighted magnetic resonance imaging (one case of each). The long-term complications were associated with larger nidus volume (p < 0.001) and a lobar location of the AVM (p < 0.01). Delayed hemorrhage was associated only with incomplete obliteration of the nidus (p < 0.05). Partial obliteration conveyed no benefit. Delayed cyst formation was associated with a higher maximal GKS dose (p < 0.001), larger nidus volume (p < 0.001), complete nidus obliteration (p < 0.01), and a lobar location of the AVM (p < 0.05).

Conclusions. Incomplete obliteration of the nidus is the most important factor associated with delayed hemorrhagic complications. Partial obliteration does not seem to reduce the risk of hemorrhage. Complete obliteration can be complicated by delayed cyst formation, especially if high maximal treatment doses have been administered.

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Masahiro Shin, Keisuke Maruyama, Hiroki Kurita, Shunsuke Kawamoto, Masao Tago, Atsuro Terahara, Akio Morita, Keisuke Ueki, Kintomo Takakura and Takaaki Kirino

Object. A large number of clinical studies have been made on treatment outcomes of radiosurgery for arteriovenous malformations (AVMs), but the reported obliteration rates following this treatment vary significantly, perhaps reflecting the different methods and timings of the imaging studies used.

Methods. The authors retrospectively analyzed their experience with gamma knife surgery in 400 patients with AVMs (follow-up period 1–135 months, median 65 months), with special reference to the imaging modality used in each case. The calculated obliteration rates varied from 68.2 to 92%, depending on imaging modality and timing of evaluation. When only unquestionable imaging data such as demonstrations of a residual nidus on computerized tomography (CT) or magnetic resonance (MR) images or findings on angiograms were used in the calculation, the obliteration rates were 72% at 3 years and 87.3% at 5 years. Factors leading to a better obliteration rate were previous hemorrhage (p = 0.0084), smaller nidus (p = 0.0023), and higher radiation dose to the lesion's margin (p = 0.0495), as determined in a multivariate analysis. Factors leading to an earlier obliteration of the nidus were male sex (p = 0.0001), previous hemorrhage (p = 0.0039), smaller nidus diameter (p = 0.0006), and dose planning using angiography alone (p = 0.0201).

Conclusions. After the introduction of CT and MR images into dose planning, the conformity and selectivity of dosimetry improved remarkably, although the latency intervals until obliteration were prolonged. Imaging outcomes for AVMs should be evaluated using data provided by longer follow-up periods. The timing of additional treatments for residual AVMs should be decided cautiously, considering the size of the AVM, the patient age and sex, and the history of hemorrhage before radiosurgery.