Measurement of tissue electrical impedance confirms stereotactically localized internal segment of the globus pallidus during surgery

Lesions surgically made in the internal segment of the posteroventral globu s pallidus (Gpi) reduce many medically intractable symptoms in patients wit h Parkinson's disease. The Gpi is localized for pallidotomy by stereotactic procedures. We sought to confirm the stereotactically localized Gpi segmen t by measuring impedance between the tip of an active electrode that was ad vanced toward the target and a remote reference electrode. A stereotactic i nstrument was used to place an active electrode in 53 conscious patients un dergoing pallidotomy. The electrode was manually advanced slowly toward the Gpi segment by a microdrive. Impedance was measured every 10 mm initially and every 1 mm in the final 10 mm of the electrode's advancement, using an impedance monitor interconnected with a lesion generator. Measurements were continued for several millimeters after each patient's target was reached. Impedance values ranged from 250 to 350 ohms throughout of the electrode p assage. Impedance increased by 25-35 ohms at 1-3 mm before the center of th e target and then dropped abruptly when the electrode passed the target. Im pedance values depended strongly on the electrode's configuration. The impe dance measurement confirmed the location of each surgical target identified by stereotactic navigation. The accuracy of the impedance measurement is a cceptable, and the procedure can be recommended as an aid to confirm the st ereotactically localized Gpi during neurological surgery. (C) 2000 Elsevier Science B.V. All rights reserved.