Right Brodmann area 18 predicts tremor arrest after Vim radiosurgery: a voxel-based morphometry study

Abstract

Drug-resistant essential tremor (ET) can benefit from open standard stereotactic procedures, such as deep-brain stimulation or radiofrequency thalamotomy. Non-surgical candidates can be offered either high-focused ultrasound (HIFU) or radiosurgery (RS). All proceduresaim to target the same thalamic site, the ventro-intermediate nucleus (e.g., Vim). The mechanisms by which tremor stops after Vim RS or HIFU remain unknown. We used voxel-based morphometry (VBM) on pretherapeutic neuroimaging data and assessed which anatomical site would best correlate with tremor arrest 1year after Vim RS. Fifty-two patients (30 male, 22 female; mean age 71.6years, range 49-82) with right-sided ET benefited from left unilateral Vim RS in Marseille, France. Targeting was performed in a uniform manner, using 130Gy and a single 4-mm collimator. Neurological (pretherapeutic and 1year after) and neuroimaging (baseline) assessments were completed. Tremor score on the treated hand (TSTH) at 1year after Vim RS was included in a statistical parametric mapping analysis of variance (ANOVA) model as a continuous variable with pretherapeutic neuroimaging data. Pretherapeutic gray matter density (GMD) was furthercorrelated with TSTH improvement. No a priori hypothesis was used in the statistical model. The only statistically significant region was right Brodmann area (BA) 18 (visual association area V2, p=0.05, cluster size Kc=71). Higher baseline GMD correlated with better TSTH improvement at 1 year after Vim RS(Spearman's rank correlation coefficient=0.002). Routine baseline structural neuroimaging predicts TSTH improvement 1year after Vim RS. The relevant anatomical area is the right visual association cortex (BA 18, V2). The question whether visual areas should be included in the targeting remains open.