title: Results of radiosurgery for brain stem arteriovenous malformations.
abstract: OBJECTIVE
  To assess the treatment results of radiosurgery for brain stem arteriovenous malformations (AVMs) and to seek optimal dose and treatment volume prescription for these lesions.
  
  
  METHODS
  The clinical and radiological data of 30 consecutive patients with brain stem AVM treated with gamma knife radiosurgery were retrospectively reviewed with a mean follow up period of 52.2 months. There were 26 patients with previous haemorrhages and 21 with neurological deficit. Seventeen AVMs were located in the midbrain, 11 in the pons, and two in the medulla oblongata. All of the lesions were small with the intra-axial component occupying less than one third of the area of brain stem parenchyma on axial section of multiplanar MRI or CT. The mean diameter of the nidus was 1.26 cm, and the nidus volume within the brain stem parenchyma ranged from 0.1 to 2.0 cm(3). The mean radiation dose to the AVM margin was 18.4 Gy.
  
  
  RESULTS
  The actuarial 3 year obliteration rate was 52.2%; 69.4% in cases treated with standard doses (minimum target dose, 18-20Gy), and 14.3% in cases treated with low doses (<18 Gy) (p<0.05). Two patients sustained symptomatic radiation injury, but there was no permanent neurological deficit caused by radiosurgery. Five patients had haemorrhage from the AVM after irradiation, including four fatal cases, resulting in a 4.0% annual rate of post-treatment bleeding.
  
  
  CONCLUSIONS
  Radiosurgery is a viable treatment modality for patients with small deep parenchymal brain stem AVMs. A standard radiosurgical dose is safe and effective when directed to a small treatment volume. However, latent interval haemorrhage remains a significant problem until the nidus is obliterated completely.
authors.affiliation: Department of Neurosurgery, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kurita
authors.forename: S
authors.initials: S
authors.lastname: Kawamoto
authors.forename: T
authors.initials: T
authors.lastname: Sasaki
authors.forename: M
authors.initials: M
authors.lastname: Shin
authors.forename: M
authors.initials: M
authors.lastname: Tago
authors.forename: A
authors.initials: A
authors.lastname: Terahara
authors.forename: K
authors.initials: K
authors.lastname: Ueki
authors.forename: T
authors.initials: T
authors.lastname: Kirino
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001933:Brain Stem / Q000098:blood supply* / Q000473:pathology; D002543:Cerebral Hemorrhage / Q000209:etiology; D002648:Child; D005260:Female; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications; D016634:Radiosurgery; D012189:Retrospective Studies; D016896:Treatment Outcome