Direct stereotactic MRI location in the globus pallidus for chronic stimulation in Parkinson's disease

We evaluated the direct location in the globus pallidus (GP) under stereota ctic MRI (sMRI) guidance in five parkinsonians treated with chronic deep br ain stimulation (four bilaterally). The sMRI consisted of three orthogonal (horizontal, frontal, sagittal) sets of images obtained with a stereotactic frame and its localiser. The sMRI was coupled with ventriculography to com pare the location with the classic indirect method based on commissural lan dmarks. The target was defined on T2-weighted slices in the anterior part o f the medial GP, at the vertex of the nucleus. It was reached via one track with a semi-micro-electrode and step by step high frequency stimulation, t hen replaced by a quadripolar electrode once wt located the site enabling t he optimal clinical improvement. Stereotactic x-rays localised the final po sition of the electrode. A company software matched sMRI, ventriculography, and peroperative (perop) x-rays. with reference to the stereotactic locati on boxes. We analysed the effects of acute (perop) and chronic (six-month f ollow-up) stimulation of active plots (acplots), i.e. leading to optimal cl inical improvement. Three distances with reference to the acplots were meas ured both on sMRI and ventriculography: the laterality from the median sagi ttal plane of the third ventricle; the anterior position from the midpoint of the intercommissural line (Icl), and the vertical position with regard t o the Id. We then compared the differences in measurements (n = 64) with th e Bland and Altman method. The mean difference was 0.09 mm with 95% of the values between +/-1 mm, but only the laterality had a statistically signifi cant agreement (all the differences included between +/- two times the stan dard deviation of the mean). The acplots distances from the dorsal, ventral , and medial boundaries of GP (defined by manual surrounding on frontal and horizontal planes) were measured on sMRI. With one exception. the acplots were all included in the nucleus. The six-month acplots were located dorsal ly with reference to the perop ones. Clinical benefit at six-months follow- up showed results comparable to the literature. Direct location of GP targe t based on sMRI seems a simple and reliable method.