Top 25 Cited Gamma Knife® Surgery Articles - Volume 111

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Masahiro Shin, Nobutaka Kawahara, Keisuke Maruyama, Masao Tago, Keisuke Ueki and Takaaki Kirino

Object. Radiosurgery has been widely adopted for the treatment of cerebral arteriovenous malformations (AVMs) in which the practical endpoint is angiographic evidence of obliteration, presumed to be consistent with elimination of the risk of hemorrhage. To test this unverified assumption, the authors followed 236 radiosurgery-treated AVMs between 1 and 133 months (median 77 months) after angiographic evidence of obliteration.

Methods. Four patients experienced hemorrhage between 16 and 51 months after angiographic confirmation of AVM obliteration, and two underwent resection. The histological findings in these patients showed occlusion of the AVM by thickening of the intimal layer with dense hyalinization as well as a small amount of residual AVM vessels and a tiny vasculature. The risks of hemorrhage from these presumaby obliterated AVMs were 0.3% for the annual bleeding risk and 2.2% for the cumulative risk over 10 years. Continuous enhancement of the nidus on computerized tomography (CT) or magnetic resonance (MR) imaging was the only significant factor positively associated with hemorrhage in the statistical analysis (p = 0.0212).

Conclusions. Because the study was based on limited follow-up data, its significance for defining predictive features of hemorrhage after angiographic evidence of obliteration is still indeterminable. Nevertheless, disappearance of the AVM on angiography after radiosurgery does not always indicate total elimination of the disease, especially when CT or MR imaging continues to demonstrate an enhancing lesion. The authors therefore recommend continual follow up even after evidence of AVM obliteration on angiography.

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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.

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Keisuke Maruyama, Douglas Kondziolka, Ajay Niranjan, John C. Flickinger and L. Dade Lunsford

Object. Management options for arteriovenous malformations (AVMs) of the brainstem are limited. The long-term results of stereotactic radiosurgery for these disease entities are poorly understood. In this report the authors reviewed both neurological and radiological outcomes following stereotactic radiosurgery for brainstem AVMs over 15 years of experience.

Methods. Fifty patients with brainstem AVMs underwent gamma knife surgery between 1987 and 2002. There were 29 male and 21 female patients with an age range of 7 to 79 years (median 35 years). Anatomical locations of these AVMs included the midbrain (39 lesions), pons (20 lesions), and medulla oblongata (three lesions). The radiation dose applied to the margin of the AVM varied from 12 to 26 Gy (median 20 Gy). Forty-five patients were followed up from 5 to 176 months (mean 72 months). The angiographically confirmed actuarial obliteration rate was 66% at the final follow-up examination. Two patients experienced a hemorrhage before obliteration. The annual hemorrhage rate was 1.7% for the first 3 years after radiosurgery and 0% thereafter. Patients who had received irradiation at two or fewer isocenters had higher obliteration rates (80% compared with 44% for > two isocenters, p = 0.006), and this was related to a more spherical nidus shape. The rate of persistent neurological complications in patients treated using magnetic resonance imaging—based dose planning after 1993 was 7%, compared with 20% in patients treated before 1993. An older patient age, a lesion located in the tectum, and a higher radiosurgery-based score were significantly associated with greater neurological complications.

Conclusions. Stereotactic radiosurgery provided complete obliteration of AVMs in two thirds of the patients with a low risk of latency-interval hemorrhage. Better three-dimensional imaging studies and conformal dose planning reduced the risk of adverse radiation effects. Younger patients harboring more spherical AVMs that did not involve the tectal plate had the best outcomes.