title: Cortical and subcortical brain shift during stereotactic procedures.
abstract: OBJECTIVE
  The success of stereotactic surgery depends upon accuracy. Tissue deformation, or brain shift, can result in clinically significant errors. The authors measured cortical and subcortical brain shift during stereotactic surgery and assessed several variables that may affect it.
  
  
  METHODS
  Preoperative and postoperative magnetic resonance imaging volumes were fused and 3D vectors of deviation were calculated for the anterior commissure (AC), posterior commissure (PC), and frontal cortex. Potential preoperative (age, diagnosis, and ventricular volume), intraoperative (stereotactic target, penetration of ventricles, and duration of surgery), and postoperative (volume of pneumocephalus) variables were analyzed and correlated with cortical (frontal cortex) and subcortical (AC, PC) deviations.
  
  
  RESULTS
  Of 66 cases, nine showed a shift of the AC by more than 1.5 mm, and five by more than 2.0 mm. The largest AC shift was 5.67 mm. Deviation in the x, y, and z dimensions for each case was determined, and most of the cortical and subcortical shift occurred in the posterior direction. The mean 3D vector deviations for frontal cortex, AC, and PC were 3.5 +/- 2.0, 1.0 +/- 0.8, and 0.7 +/- 0.5 mm, respectively. The mean change in AC-PC length was -0.2 +/- -0.9 mm (range -4.28 to 1.66 mm). The volume of postoperative pneumocephalus, assumed to represent cerebrospinal fluid (CSF) loss, was significantly correlated with shift of the frontal cortex (r = 0.640, 64 degrees of freedom, p < 0.001) and even more strongly with shift of the AC (r = 0.754, p < 0.001). No other factors were significantly correlated with AC shift. Interestingly, penetration of the ventricles during electrode insertion, whether unilateral or bilateral, did not affect volume of pneumocephalus.
  
  
  CONCLUSIONS
  Cortical and subcortical brain shift occurs during stereotactic surgery as a direct function of the volume of pneumocephalus, which probably reflects the volume of CSF that is lost. Clinically significant shifts appear to be uncommon, but stereotactic surgeons should be vigilant in preventing CSF loss.
authors.affiliation: Department of Neurological Surgery, University of Virginia Health System, Charlottesville, Virginia 22908, USA. wje4r@virginia.edu
authors.forename: W Jeffrey
authors.initials: WJ
authors.lastname: Elias
authors.forename: Kai-Ming
authors.initials: KM
authors.lastname: Fu
authors.forename: Robert C
authors.initials: RC
authors.lastname: Frysinger
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011007:Pneumocephalus; D012189:Retrospective Studies; D013238:Stereotaxic Techniques