title: The silent loss of neuronavigation accuracy: a systematic retrospective analysis of factors influencing the mismatch of frameless stereotactic systems in cranial neurosurgery.
abstract: BACKGROUND
  Neuronavigation has become an intrinsic part of preoperative surgical planning and surgical procedures. However, many surgeons have the impression that accuracy decreases during surgery.
  
  
  OBJECTIVE
  To quantify the decrease of neuronavigation accuracy and identify possible origins, we performed a retrospective quality-control study.
  
  
  METHODS
  Between April and July 2011, a neuronavigation system was used in conjunction with a specially prepared head holder in 55 consecutive patients. Two different neuronavigation systems were investigated separately. Coregistration was performed with laser-surface matching, paired-point matching using skin fiducials, anatomic landmarks, or bone screws. The initial target registration error (TRE1) was measured using the nasion as the anatomic landmark. Then, after draping and during surgery, the accuracy was checked at predefined procedural landmark steps (Mayfield measurement point and bone measurement point), and deviations were recorded.
  
  
  RESULTS
  After initial coregistration, the mean (SD) TRE1 was 2.9 (3.3) mm. The TRE1 was significantly dependent on patient positioning, lesion localization, type of neuroimaging, and coregistration method. The following procedures decreased neuronavigation accuracy: attachment of surgical drapes (DTRE2 = 2.7 [1.7] mm), skin retractor attachment (DTRE3 = 1.2 [1.0] mm), craniotomy (DTRE3 = 1.0 [1.4] mm), and Halo ring installation (DTRE3 = 0.5 [0.5] mm). Surgery duration was a significant factor also; the overall DTRE was 1.3 [1.5] mm after 30 minutes and increased to 4.4 [1.8] mm after 5.5 hours of surgery.
  
  
  CONCLUSIONS
  After registration, there is an ongoing loss of neuronavigation accuracy. The major factors were draping, attachment of skin retractors, and duration of surgery. Surgeons should be aware of this silent loss of accuracy when using neuronavigation.
authors: Department of Neurosurgery, Bern University Hospital, Bern, Switzerland. Lennart@Stieglitze.de
authors: Lennart Henning
authors: LH
authors: Stieglitz
authors: Jens
authors: J
authors: Fichtner
authors: Robert
authors: R
authors: Andres
authors: Philippe
authors: P
authors: Schucht
authors: Ann-Kathrin
authors: AK
authors: Krähenbühl
authors: Andreas
authors: A
authors: Raabe
authors: Jürgen
authors: J
authors: Beck
mesh_terms: D059925:Anatomic Landmarks; D001927:Brain Diseases / Q000601:surgery*; D002138:Calibration; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D038361:Neuronavigation / Q000295:instrumentation* / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity