title: Quantitative analysis of the transcondylar approach to the foramen magnum.
abstract: OBJECTIVE
  Condylar resection with suboccipital craniotomy increases foramen magnum exposure, but guidelines for when this is necessary are not defined. Cadaveric and computed tomography evaluations were completed to guide decision-making regarding the use and extent of condylar resection.
  
  
  METHODS
  Quantitative analysis of foramen magnum surgical exposures was performed on 32 skulls (64 sides) and 6 cadaveric dissections (12 sides). Computed tomographic (CT) scans were performed on cadaveric heads before and after condylar resections. Digitized images of dry skulls and CT images of cadaver heads were quantitatively analyzed. Predissection CT measurements of cadaveric heads guided extent of condylar resections, and resection accuracy was assessed with postdissection CT scans.
  
  
  RESULTS
  Skull measurements (means in parentheses) included the foramen magnum area (7.8 cm(2)), length (3.6 cm), width (3.1 cm), anteroposterior condylar length (2.3 cm), and axial condylar length (2.5 cm). Mean widths of potential surgical exposures for skulls were obtained for A) suboccipital craniotomy (2.3 cm), B) with 25% (2.6 cm), and C) 50% condylar resection (3.0 cm). Mean angles of exposure were as follows: A, 38.4 degrees; B, 49.1 degrees; and C, 54.3 degrees. CT scans of cadaveric heads before and after dissections yielded measurements of exposure equivalent to measurements found on the dry skulls.
  
  
  CONCLUSIONS
  On average, lateral exposure increases by 3 mm (13%) and 7 mm (30%) for 25 and 50% condylar resection, respectively, compared with suboccipital craniotomy alone. Angles of exposure increase by 10.7 degrees (28%) and 15.9 degrees (41%). Measurements of CT images can be used preoperatively to help analyze the need for condylar resection and intraoperatively to guide the extent of condylar resection.
authors.affiliation: Department of Neurological Surgery, Washington University School of Medicine, 4566 Scott Avenue, St. Louis, MO 63110, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Wanebo
authors.forename: M R
authors.initials: MR
authors.lastname: Chicoine
mesh_terms: D000328:Adult; D002508:Cephalometry; D003399:Craniotomy / Q000379:methods*; D005260:Female; D005539:Foramen Magnum / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008335:Mandibular Condyle / Q000000981:diagnostic imaging / Q000601:surgery*; D008432:Mathematical Computing; D008866:Microsurgery; D012015:Reference Standards; D014057:Tomography, X-Ray Computed