Evaluation of Bilateral Gamma Knife Thalamotomy in Patients Presenting With Severe Essential Tremor

Inclusion Criteria: * Patients with essential tremor defined criteria Consensus statement of the movement Disorder Society on Classical Essential Tremor (1998), with trembling of the upper limbs causing functional impairment justifying surgical therapy. * Man or woman aged 20 to 85 years. * Patient having an absolute contraindication against or on Deep Brain Stimulation (DBS) of the VIM. * Patient who received a first effective unilateral thalamotomy on tremor with a satisfactory clinical outcome (no cognitive impairment, lack of postural disorder Musculoskeletal severe lack of dysarthria). The first effective thalamotomy will be characterized by an improved score of tremor ≥ 45% and improved functional gene ≥ 50%. * Patient who received a first unilateral thalamotomy with satisfactory radiological evolution. Unsatisfactory radiological evolution will be characterized by a contrast uptake\> 350 mm3 one year with edema on T2 and Flair sequences extended beyond the internal capsule. * Patient requiring contralateral treatment because of the severity of the tremor and functional impairment. * Patient affiliated to a social protection scheme. * Patient who understood and signed the informed consent form (signature of a third person possible when the patient is unable to read and / or write but in a state to give consent). Exclusion Criteria: * Patient with against-indication for performing a brain MRI (pacemaker, intracranial metallic objects etc.) * Patient with an against-indication to radiosurgical treatment (prior treatment with cerebral radiotherapy) * Pregnant or lactating women * Women of childbearing potential unless 1. surgical sterilization 2. use of effective contraception (intrauterine device or method more hormonal barrier method), and requiring to present a test pregnancy by assaying the negative serum with chorionic gonadotrope hormon (CGH) when selecting and accept to remain under the current form of contraception for the duration of the study (in women past menopause should be amenorrheic for at least 12 months to be considered as no longer able to bear a child). * simultaneous participation in another clinical trial or exclusion period of a previous clinical trial. * vulnerable persons: minors, protected adults (guardianship) and Major unable to consent.