title: Electromagnetic navigation-guided surgery in the semi-sitting position for posterior fossa tumours: a safety and feasibility study.
abstract: BACKGROUND
  Electromagnetic (EM)-guided neuronavigation is an innovative technique and a viable alternative to opto-electric navigation. We have performed a safety and feasibility study using EM-guided neuronavigation for posterior fossa surgery in the semi-sitting position in a selected subset of patients.
  
  
  METHODS
  Out of 284 patients with posterior fossa tumours operated upon over a period of 40 months, a subset of 15 patients was thought to possibly benefit from EM navigational guidance and was included in this study. There were six children and nine adults (aged between 8 and 84 years; mean age, 34.6 years) with different neoplasms in the brainstem or close to the midline. All patients had contrast-enhanced three-dimensional (3D) magnetic resonance imaging (MRI) of the head preoperatively. EM-guided navigation was used to identify and preserve the venous sinuses during craniotomy and to determine the trajectory to the lesion using various approaches. Neuronavigation accuracy was repeatedly checked for deviations measured in millimetres on screen shots during surgery before and after dural opening in the coronal (z = vertical), axial (x = mediolateral) and sagittal (y = anteroposterior) plane.
  
  
  RESULTS
  Referencing of the patient in the supine position was fast and easy. There was no loss of navigation accuracy after repositioning of the patient in the semi-sitting position (mean, 2.5 mm ± 0.92 mm). Identification of the pathological structure using EM navigation was achieved in all instances. Optimal angulation of the neck was selected individually to permit a comfortable position for the surgeon with full access to the lesion avoiding over-flexion. Deviation of accuracy at the surface of the target lesion ranged between 2.5 and 5.8 mm (mean, 3.9 mm ± 1.1 mm).
  
  
  CONCLUSIONS
  EM-guided neuronavigation in the semi-sitting position was safe and technically feasible. It enabled fast and accurate referencing without loss of navigation accuracy despite repositioning of the patient. In contrast to conventional opto-electric neuronavigation there were no line of sight problems.
authors.affiliation: Department of Neurosurgery, Medical School Hannover, Carl-Neuberg-Str.1, 30625, Hannover, Germany, hermann.elvis@mh-hannover.de.
authors.forename: Elvis J
authors.initials: EJ
authors.lastname: Hermann
authors.forename: Ioannis
authors.initials: I
authors.lastname: Petrakakis
authors.forename: Manolis
authors.initials: M
authors.lastname: Polemikos
authors.forename: Peter
authors.initials: P
authors.lastname: Raab
authors.forename: Zafer
authors.initials: Z
authors.lastname: Cinibulak
authors.forename: Makoto
authors.initials: M
authors.lastname: Nakamura
authors.forename: Joachim K
authors.initials: JK
authors.lastname: Krauss
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D003388:Cranial Fossa, Posterior / Q000473:pathology / Q000601:surgery*; D004574:Electromagnetic Fields / Q000009:adverse effects; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D038361:Neuronavigation / Q000009:adverse effects / Q000379:methods*; D019635:Neurosurgical Procedures / Q000009:adverse effects / Q000379:methods*; D056888:Patient Positioning / Q000379:methods*; D019292:Skull Base Neoplasms / Q000601:surgery*; D055815:Young Adult