Targeting of the pedunculopontine nucleus by an MRI-guided approach: a cadaver study

Laboratory evidence suggests that the pedunculopontine nucleus (PPN) plays a central role in the initiation and maintenance of gait. Translational research has led to reports on deep brain stimulation (DBS) of the rostral brainstem in parkinsonian patients. However, initial clinical results appear to be rather variable. Possible factors include patient selection and the wide variability in anatomical location of implanted electrodes. Clinical studies on PPN DBS efficacy would, therefore, benefit from an accurate and reproducible method of stereotactic localization of the nucleus. The present study evaluates the anatomical accuracy of a specific protocol for MRI-guided stereotactic targeting of the PPN in a human cadaver. Imaging at 1.5 and 9.4 T confirmed electrode location in the intended region as defined anatomically by the surrounding fiber tracts. The spatial relations of each electrode track to the nucleus were explored by subsequent histological examination. This confirmed that the neuropil surrounding each electrode track contained scattered large neurons morphologically consistent with those of the subnucleus dissipatus and compactus of the PPN. The results support the accuracy of the described specific MR imaging protocol.