Stereotactic radiosurgical pallidotomy and thalamotomy with the gamma knife: MR imaging findings with clinical correlation - Preliminary experience

PURPOSE: To evaluate the temporal evolution and appearance of a radiosurgic al lesion at magnetic resonance (MR) imaging and the clinical response in p atients undergoing stereotactic radiosurgical pallidotomy or thalamotomy wi th the gamma knife. MATERIALS AND METHODS: Seventeen patients with medically refractory movemen t disorders underwent stereotactic radiosurgical pallidotomy (n = 2) or tha lamotomy (n = 15). A single dose of 120-140 Gy was administered to a target in the globus pallidus interna or ventralis intermedius thalamic nucleus. Postprocedure gadolinium-enhanced MR imaging and clinical assessment were p erformed at 1 month and 3 months. RESULTS: At 3 months, the radiosurgical lesion most commonly (n = 11) appea red as a ring-enhancing focus 5 mm or less in diameter surrounded by vasoge nic edema that extended less than 7 mm in radius beyond the target. Five pa tients had ring-enhancing lesions 7 mm or more in diameter; four of these d eveloped symptomatic perilesional edema at 3 (n = 2) or 8 (n = 2) months af ter the procedure. Onset of therapeutic effect began approximately 4 weeks after treatment. In the 15 patients with tremor, there was a mean decline o f 2.1 on the Tremor Rating Scale. CONCLUSION: Findings in this pilot study suggest that radiosurgical thalamo tomy is a promising treatment for medically refractory tremor. Three-month follow-up Mr studies show a ring-enhancing lesion surrounded by a variable amount of vasogenic edema. Visualization of the radiosurgical lesion and th e clinical response are delayed compared to that with radio-frequency proce dures.