title: Comparative analysis of spinal extradural arteriovenous fistulas with or without intradural venous drainage: a systematic literature review.
abstract: OBJECTIVE
  Spinal arteriovenous malformations (AVMs) are classified into types according to anatomical characteristics: dural arteriovenous fistulas (AVFs), intramedullary AVMs, perimedullary AVFs, and extradural AVFs. Spinal extradural AVFs are much rarer than other types of spinal AVMs, and the available literature on this clinical entity has been based only on case reports or small case series. To investigate the clinical characteristics of patients with spinal extradural AVFs, the authors systematically reviewed the associated literature in the MRI era.
  
  
  METHODS
  The PubMed database was searched for all relevant English-language case reports and case series published from 1990 to 2011. The clinical differences between Type A with and Type B without intradural venous drainage were statistically compared, especially regarding clinical features and angiographic and MRI findings.
  
  
  RESULTS
  Forty-five cases of spinal extradural AVFs were found. Type A spinal extradural AVFs were diagnosed in patients with a significantly older age (mean 63.5 years) as compared with Type B AVFs (mean 34.3 years, p < 0.0001). Most cases of Type A spinal extradural AVFs exhibited a diffuse high signal intensity of the spinal cord on T2-weighted MR images and no mass effect (p < 0.0001), and they commonly occurred in the thoracolumbar and lumbar regions (p < 0.0001). On the other hand, cases of Type B lesions exhibited a normal signal intensity of the cord with severe mass effect due to an enlarged extradural venous plexus, and they commonly occurred in the cervical and upper thoracic regions (p < 0.0001), frequently in patients with neurofibromatosis Type 1 (p = 0.049). Because Type B AVFs consisted of high-flow, multiple complex anastomoses between arteries and the epidural venous plexus, patients with these lesions tended to undergo multisession treatments, and the rate of partial AVF occlusion was significantly higher than for Type A AVFs (p = 0.018), although there was no difference in symptom outcomes between the 2 groups.
  
  
  CONCLUSIONS
  To the best of the authors' knowledge, a comparative analysis of the clinical differences in patients with extradural AVFs with or without intradural venous drainage has yet to be described in the literature. They concluded that in the diagnosis of spinal extradural AVF, evaluation of intradural venous drainage is important because the cause of myelopathy determines the treatment goals.
authors.affiliation: Department of Neurosurgery, Tokyo Metropolitan Neurological Hospital, Tokyo, Japan. takai-nsu@umin.ac.jp
authors.forename: Keisuke
authors.initials: K
authors.lastname: Takai
authors.forename: Makoto
authors.initials: M
authors.lastname: Taniguchi
mesh_terms: D000368:Aged; D001165:Arteriovenous Malformations / Q000601:surgery*; D016206:Databases, Bibliographic / Q000706:statistics & numerical data; D004322:Drainage / Q000379:methods*; D004388:Dura Mater / Q000098:blood supply / Q000601:surgery; D004621:Embolization, Therapeutic; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013116:Spinal Cord / Q000098:blood supply*