Impedance monitoring in the stereotactic localization of intracranial structures.

Measurement of tissue impedance is a simple objective method for the localization of intracranial structures. Continuous bipolar impedance monitoring was performed during various CT-guided stereotactic procedures in 36 patients with brain pathology. The obtained values of the impedance profile along the trajectory were compared with the tissue density on CT scans or angled coronal and sagital CT reconstructions intraoperatively. The main goal was the selection of optimal biopsy targets and safe probe trajectory. Histologic findings of serial transtumoral biopsy were retrospectively correlated with both CT (or MRI) transposed data and patterns of tissue impedance. Intraoperative impedance monitoring enhanced the accuracy and safety of CT-guided procedures. The histologic examination of representative tissue samples avoids the risks of "blind" surgical or radiation management. This technique is reported with 6 illustrative cases.