Can neuronavigation contribute to standardization of selective amygdalohippocampectomy?

Tailored selective amygdalohippocampal resections seem to be an interesting application for neuronavigation. The accuracy of freehand frameless neuronavigation was assessed in 28 patients for its ability to determine the hippocampal resection length, as compared to postoperative MRI. Brain collapse due to CSF displacement caused an expected error of navigation at the brain surface, but almost no error at the tentorial notch. Yet, the hippocampal resection length was overestimated by navigation to an extent of 3 +/- 2 mm. The discrepancy is explained by an anterior-posterior component of brain collapse in a tilted head. Horizontal positioning of the head or navigational marking prior to the occurrence of brain collapse may overcome the problem.