title: En bloc resection of sacral chordomas aided by frameless stereotactic image guidance:  a technical note.
abstract: BACKGROUND
  The most important predictor of survival for patients with sacral chordomas is an initial en bloc resection with negative margins. However, obtaining negative margins can be technically challenging. Intraoperative navigation may be helpful in attempting an excision with negative margins.
  
  
  OBJECTIVE
  This is the first report of partial sacrectomy guided by frameless stereotactic navigation.
  
  
  METHODS
  Three patients with a mean age of 58.7 years underwent en bloc resection of sacral chordomas aided by image guidance. Intraoperatively, the reference arc was clamped to the spinous process of L5 and the bony landmarks of S1 were used for registration. Subsequently, the drill was registered, allowing the osteotomy trajectory to be visualized in real time with reference to the patients' anatomy and tumor location.
  
  
  RESULTS
  None of the patients had any intraoperative or postoperative complications. Two patients with smaller tumors (5 cm) had negative margins, whereas the third patient with an 11.5 cm tumor had marginal margins. With an average follow-up of 44 months, none of the patients have had a recurrence of the tumor.
  
  
  CONCLUSIONS
  The use of frameless stereotaxy during the en bloc resection of sacral tumors is safe and feasible. Frameless stereotactic navigation was a useful adjunct to preoperative imaging and to the surgeon's anatomic knowledge. Image guidance was used during the osteotomies to decrease the likelihood of injury to vital adjacent structures or violation of the tumor capsule and to increase the likelihood that the appropriate surrounding tissue was resected to attempt a wide or marginal resection.
authors.affiliation: Department of Neurosurgery, The Johns Hopkins University, Baltimore, Maryland 21287, USA.
authors.forename: Hormuzdiyar H
authors.initials: HH
authors.lastname: Dasenbrock
authors.forename: Michelle J
authors.initials: MJ
authors.lastname: Clarke
authors.forename: Ali
authors.initials: A
authors.lastname: Bydon
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: McGirt
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Witham
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sciubba
authors.forename: Ziya L
authors.initials: ZL
authors.lastname: Gokaslan
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Wolinsky
mesh_terms: D000328:Adult; D000368:Aged; D002817:Chordoma / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000517:prevention & control; D008297:Male; D038361:Neuronavigation / Q000379:methods*; D019635:Neurosurgical Procedures / Q000379:methods*; D010027:Osteotomy / Q000379:methods; D011128:Polyradiculopathy / Q000517:prevention & control; D011183:Postoperative Complications / Q000517:prevention & control; D012189:Retrospective Studies; D012447:Sacrum / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome