title: Factors affecting successful localization of the central sulcus using the somatosensory evoked potential phase reversal technique.
abstract: BACKGROUND
  Perirolandic surgery is associated with an increased risk of postoperative neurological deficit that can be reduced by accurate recognition of the location of sensorimotor cortex. The median somatosensory evoked potential (MSSEP) phase reversal technique (PRT) reliably identifies the central sulcus (CS) intraoperatively, but does require additional surgical time. Awareness of factors that lengthen the time required for MSSEP PRT has important implications for surgical planning.
  
  
  OBJECTIVE
  To identify factors that affect the time required for CS localization via MSSEP PRT.
  
  
  METHODS
  Multivariate Cox regression analysis, applied in 100 consecutive cases of perirolandic surgery at a single institution from 2005 to 2010, during which CS localization was attempted via a standardized MSSEP PRT.
  
  
  RESULTS
  The CS was reliably identified in 77 cases. The mean time to identification was 5 minutes (SD = 5; range, 1-20 minutes). Lesion location either very close to the CS (within the postcentral gyrus) or at an intermediate distance (with edema extending very close to the CS) independently decreased the rate at which the CS was identified by 73% (hazard ratio: 0.27, P < .001) and 55% (hazard ratio: 0.45, P = .007), respectively. Highly destructive pathology reduced this rate by 42% (hazard ratio: 0.58, P = .03), after adjusting for other important factors. Epidural recording, age, and the presence of a burst suppression pattern on the electroencephalogram had no effect.
  
  
  CONCLUSIONS
  MSSEP PRT is an effective method for CS identification and only marginally lengthens the operative time. However, difficulty in CS localization can be expected in the presence of postcentral gyrus lesions, edema distorting perirolandic anatomy, and with highly destructive pathology.
authors: Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA. sheth@post.harvard.edu
authors: Sameer A
authors: SA
authors: Sheth
authors: Christine A
authors: CA
authors: Eckhardt
authors: Brian P
authors: BP
authors: Walcott
authors: Emad N
authors: EN
authors: Eskandar
authors: Mirela V
authors: MV
authors: Simon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001900:Boston / Q000453:epidemiology; D001927:Brain Diseases / Q000175:diagnosis* / Q000453:epidemiology / Q000601:surgery*; D001931:Brain Mapping / Q000379:methods*; D002648:Child; D004569:Electroencephalography / Q000379:methods*; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D061646:Operative Time; D011183:Postoperative Complications / Q000453:epidemiology / Q000517:prevention & control*; D011300:Preoperative Care / Q000379:methods / Q000706:statistics & numerical data; D015995:Prevalence; D016016:Proportional Hazards Models; D015203:Reproducibility of Results; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D013003:Somatosensory Cortex; D016896:Treatment Outcome; D055815:Young Adult