Deep brain nucleus targeting in Parkinson's disease and essential tremor by image guided surgery using neuronavigation system with tractography and volume of tissue of activated assessment.

OBJECTIVE: Deep Brain Stimulation (DBS) is an effective surgical approach for treatment of Parkinson's disease (PD), dystonia and essential tremor (ET). Traditionally, DBS is performed using frame-based stereotactic technique. Recently, image guided surgery (IGS) using neuronavigation has gained popularity in neurosurgical procedures. We aim to investigate whether DBS using neuronavigation is capable of improving patient's outcome and minimize its complications.

SUBJECT AND METHODS: From February 2011 to October 2016, 20 patients with PD and 6 patients with ET were enrolled in the study. Patients aged between 18 to 70 years, were included and they underwent Magnetic Resonance Imaging (MRI) for deep brain nucleus volumetry. Among PD patients, 14 cases underwent subthalamic nucleus (STN) implantation, while other 6 cases underwent globus pallidus internus (GPi) implantation. Furthermore, ventral intermediate nucleus (VIN) implantation was performed for ET patients, all with IGS using neuronavigation system. Patients were assessed by unified Parkinson's disease rating scale (UPDRS) for PD and tremor scores for ET in their follow ups. Authors utilized Butson model for volume of tissue activated (VTA) assessment. In addition, detailed tractography was performed to evaluate white matter circuits radiating from deep nucleuses.

RESULTS: PD patients with GPi volume of more than 600mm3 and less than 400mm3 were excluded from the study. Mean right and left GPi volume was 519±94.2mm3 and 480±80.3mm3 , respectively. Calculated VTA based on Butson model revealed that 70% of cases who exhibited improved UPDRS of more than 50% in the 7th month of follow-up, had their VTA outside their defined GPi and STN boundaries with outer layer overlap. In contrast, 60% of cases who showed UPDRS improvement of less than 50% in same follow-up month, have their VTA inside defined GPi and STN boundaries. Moreover, ET patients experienced mean 55% and 79% improvement in tremor scores at mean 6.7 and 9.9 follow up month respectively. No surgery related complications were observed. Furthermore, tractography analysis revealed increased superior frontal gyrus and thalamus connection in patients with improved UPDRS.

CONCLUSION: IGS using neuronavigation allowed more accurate deep nucleus targeting, minimized intra- and post-operative complications and improved clinical outcome in DBS candidate patients. Our study revealed that increased white matter connections with remote parts of the brain would suggest that isolated deep nucleus stimulation could not explain symptom recovery and that patients' specific white matter stimulation by tractography coupled with IGS should be in priority.