title: Radiation-induced imaging changes following Gamma Knife surgery for cerebral arteriovenous malformations.
abstract: OBJECTIVE
  The objective of this study was to evaluate the incidence, severity, clinical manifestations, and risk factors of radiation-induced imaging changes (RIICs) following Gamma Knife surgery (GKS) for cerebral arteriovenous malformations (AVMs).
  
  
  METHODS
  A total of 1426 GKS procedures performed for AVMs with imaging follow-up available were analyzed. Radiation-induced imaging changes were defined as newly developed increased T2 signal surrounding the treated AVM nidi. A grading system was developed to categorize the severity of RIICs. Grade I RIICs were mild imaging changes imposing no mass effect on the surrounding brain. Grade II RIICs were moderate changes causing effacement of the sulci or compression of the ventricles. Grade III RIICs were severe changes causing midline shift of the brain. Univariate and multivariate logistic regression analyses were applied to test factors potentially affecting the occurrence, severity, and associated symptoms of RIICs.
  
  
  RESULTS
  A total of 482 nidi (33.8%) developed RIICs following GKS, with 281 classified as Grade I, 164 as Grade II, and 37 as Grade III. The median duration from GKS to the development of RIICs was 13 months (range 2-124 months). The imaging changes disappeared completely within 2-128 months (median 22 months) following the development of RIICs. The RIICs were symptomatic in 122 patients, yielding an overall incidence of symptomatic RIICs of 8.6%. Twenty-six patients (1.8%) with RIICs had permanent deficits. A negative history of prior surgery, no prior hemorrhage, large nidus, and a single draining vein were associated with a higher risk of RIICs.
  
  
  CONCLUSIONS
  Radiation-induced imaging changes are the most common adverse effects following GKS. Fortunately, few of the RIICs are symptomatic and most of the symptoms are reversible. Patients with a relatively healthy brain and nidi that are large, or with a single draining vein, are more likely to develop RIICs.
authors.affiliation: Department of Neurological Surgery, University of Virginia, Charlottesville, Virginia 22908, USA. cy4f@virginia.edu
authors.forename: Chun-Po
authors.initials: CP
authors.lastname: Yen
authors.forename: Julie A
authors.initials: JA
authors.lastname: Matsumoto
authors.forename: Max
authors.initials: M
authors.lastname: Wintermark
authors.forename: Lucia
authors.initials: L
authors.lastname: Schwyzer
authors.forename: Avery J
authors.initials: AJ
authors.lastname: Evans
authors.forename: Mary E
authors.initials: ME
authors.lastname: Jensen
authors.forename: Mark E
authors.initials: ME
authors.lastname: Shaffrey
authors.forename: Jason P
authors.initials: JP
authors.lastname: Sheehan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011859:Radiography; D016634:Radiosurgery / Q000009:adverse effects* / Q000379:methods; D012307:Risk Factors; D016896:Treatment Outcome