title: Late cyst formation following gamma knife surgery of arteriovenous malformations.
abstract: OBJECTIVE
  The authors present data concerning the development of cysts following gamma knife surgery (GKS) in 1203 consecutive patients with arteriovenous malformations (AVMs) treated by the senior author (L.S.). The cyst was defined as a fluid-filled cavity at the site of a treated AVM. Cases involving regions corresponding to previous hematoma cavities were excluded. The incidence of cyst formation was assessed using magnetic resonance imaging studies performed in 196 cases with more than 10 years of follow up, in 332 cases with 5 to 10 years of follow up, and in 675 cases with less than 5 years of follow up. One hundred five cases were lost to follow-up study. The Cox regression method was used to analyze the factors related to cyst formation.
  
  
  METHODS
  The incidence of cyst formation in the entire patient population was 1.6 and 3.6% in those undergoing follow-up examination for more than 5 years. Ten of 20 cysts developed between 10 to 23 years, nine between 5 to 10 years, and one in less than 5 years following the treatment. Cyst fluid aspiration, cystoperitoneal shunt placement, or craniotomy were used in three symptomatic cases. Analysis of age, sex, and treatment parameters yielded no significant relationship with cyst formation; however, radiation-induced tissue change following GKS (p = 0.027) and prior embolization (p = 0.011) were related to cyst formation.
  
  
  CONCLUSIONS
  Overall, the incidence of cyst formation in patients who underwent GKS for AVM was 1.6%. The development of the cyst was related to the duration of the follow-up period. When cysts are symptomatic, surgical intervention should be performed.
authors.affiliation: Lars Leksell Center of Gamma Knife Surgery, Department of Neurological Surgery, University of Virginia, Charlottesville, Virginia 22908, USA.
authors.forename: Hung-Chuan
authors.initials: HC
authors.lastname: Pan
authors.forename: Jason
authors.initials: J
authors.lastname: Sheehan
authors.forename: Matei
authors.initials: M
authors.lastname: Stroila
authors.forename: Melita
authors.initials: M
authors.lastname: Steiner
authors.forename: Ladislau
authors.initials: L
authors.lastname: Steiner
mesh_terms: D000293:Adolescent; D000328:Adult; D001927:Brain Diseases / Q000209:etiology* / Q000473:pathology; D002648:Child; D003560:Cysts / Q000209:etiology* / Q000473:pathology; D005260:Female; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D011183:Postoperative Complications; D011829:Radiation Dosage