POSTIMAGING BRAIN DISTORTION - MAGNITUDE, CORRELATES, AND IMPACT ON NEURONAVIGATION

Object. This prospective study was conducted to quantify brain shifts during open cranial surgery, to determine correlations between these s hifts and image characteristics, and to assess the impact of postimagi ng brain distortion on neuronavigation. Methods. During 48 operations, movements of the cortex on opening, the deep tumor margin, and the co rtex at completion were measured relative to the preoperative image po sition with the aid of an image-guidance system. Bone surface offset w as used to assess system accuracy and correct for registration errors. Preoperative images were examined for the presence of edema and to de termine tumor volume, midline shift, and depth of the lesion below the skin surface. Results were analyzed for all cases together and separa tely for four tumor groups: 13 meningiomas, 18 gliomas, 11 nonglial in traaxial lesions, and six skull base lesions. For all 48 cases the mea n shift of the cortex after dural opening was 4.6 mm, shift of the dee p tumor margin was 5.1 mm, and shift of the cortex at completion was 6 .7 mm. Each tumor group displayed unique patterns of shift, with signi ficantly greater shift at depth in meningiomas than gliomas (p = 0.007 ) and significantly less shift in skull base cases than other groups ( p = 0.003). Whereas the preoperative image characteristics correlating with shift of the cortex on opening were the presence of edema and de pth of the tumor below skin surface, predictors of shift at depth were the presence of edema, the lesion volume, midline shift, and magnitud e of shift of the cortex on opening. Conclusions. This study quantifie d intraoperative brain distortion, determined the different behavior o f tumors in four pathological groups, and identified preoperative pred ictors of shift with which the reliability of neuronavigation may be e stimated.