title: Acquired Chiari Malformation and Syringomyelia Secondary to Space-Occupying Lesions: A Systematic Review.
abstract: BACKGROUND
  Acquired Chiari malformations (ACM) and associated syringomyelia secondary to space-occupying lesions can cause neurologic deficits independent of or in combination with the offending mass. Although type I Chiari malformations are traditionally treated with posterior fossa decompression, optimal surgical management of ACM and associated syringomyelia remains unclear. The purpose of this study is to review the current literature surrounding the management of ACM.
  
  
  METHODS
  A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Using the relevant keywords, articles were identified through multiple databases from inception to April 2016. Our primary outcome was postoperative resolution of tonsillar herniation, syringomyelia, and clinical symptoms and signs.
  
  
  RESULTS
  Thirty studies (27 case reports and 3 case series), encompassing 44 patients, were included in the review. Meningiomas (36%) and arachnoid cysts (32%) were the lesions most commonly associated with ACM. Offending lesions were usually large (85%) and almost all were found in the posterior fossa (89%). Syringomyelia was present in 82% of cases. Overall, all but 1 patient had improvement or resolution of their syringomyelia after surgery and none required a syrinx shunt. Rates of tonsillar ascent, syrinx resolution, and neurologic recovery were similar in patients who underwent lesion removal alone versus those who underwent posterior fossa decompression and lesion removal.
  
  
  CONCLUSIONS
  Space-occupying lesions in the posterior fossa are a rare cause of ACM and syringomyelia. Surgical management of the underlying lesion improves ACM and associated syringomyelia without the need for syrinx shunting.
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Justin
authors.initials: J
authors.lastname: Wang
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, Ontario, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Naif M
authors.initials: NM
authors.lastname: Alotaibi
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Nardin
authors.initials: N
authors.lastname: Samuel
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, Ontario, Canada.
authors.forename: George M
authors.initials: GM
authors.lastname: Ibrahim
authors.affiliation: Department of Neurosurgery, David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
authors.forename: Aria
authors.initials: A
authors.lastname: Fallah
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, Ontario, Canada; Division of Neurosurgery, St Michael's Hospital, Toronto, Ontario, Canada; Neuroscience Research Program, Keenan Research Centre of the Li Ka Shing Knowledge Institute of St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada. Electronic address: Mountain@smh.ca.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Cusimano
mesh_terms: D000293:Adolescent; D000328:Adult; D016080:Arachnoid Cysts / Q000150:complications* / Q000000981:diagnostic imaging / Q000601:surgery; D001139:Arnold-Chiari Malformation / Q000000981:diagnostic imaging / Q000209:etiology* / Q000601:surgery; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D008579:Meningioma / Q000150:complications* / Q000000981:diagnostic imaging; D008875:Middle Aged; D010608:Pharyngeal Diseases / Q000150:complications / Q000000981:diagnostic imaging / Q000601:surgery; D011871:Radiology; D013595:Syringomyelia / Q000000981:diagnostic imaging / Q000209:etiology* / Q000601:surgery; D016896:Treatment Outcome; D055815:Young Adult
keywords: Acquired; Chiari malformation; Cyst; Lesion; Syringomyelia; Tumor