Correspondence of microelectrode mapping with magnetic resonance imaging for subthalamic nucleus procedures

BACKGROUND: Magnetic resonance imaging (MRI) and microelectrode recording (MER) are commonly used to guide stereotactic procedures on the subthalamic nucleus (STN). Little is known about the correlation between the position of the STN as seen on MRI and that as determined by MER mapping. We compared these in 10 patients with Parkinson's disease. METHODS: The position of the STN was determined by intraoperative MER findings and stereotactic axial T2 magnetic resonance images with 2-mm slice thickness. Images were reconstructed in a 3-dimensional workstation. The anterior, posterior, medial, lateral, dorsal, and ventral borders of the STN defined with the MRI were measured relative to the midcommissural point. The location of STN activity during MER was reconstructed relative to the midcommissural point for comparison. RESULTS: Twenty-nine tracks recorded with microelectrodes provided clear spans of STN-like activity in 18 STN nuclei. The coordinates of MER were, in general, within the borders of the STN defined with the MRI. However, when analyzed individually, some of the tracks had STN-like activity outside the borders of the MRI-defined nucleus (mostly <1 mm). Three tracks had STN-like activity recorded between 2 and 3 mm more anterior than the anterior border of the nucleus defined with the MRI. CONCLUSIONS: There was a good correlation between MER and the borders of the STN defined in the MRI, except for the anterior-posterior axis, in which MER indicated that the STN extended more anteriorly than as suggested by MRI. This should be taken into account in STN surgery.