MR imaging of stereotactic thalamotomy using radiofrequency methods

Sixty-eight stereotactic radiofrequency (rf) thalamic lesions in 57 patients with movement disorders were evaluated by magnetic resonance (MR) imaging. Postoperative periods ranged from 5 days to 4 years and 9 months. All 68 rf lesions were clearly detected on T2-weighted images (T2WI). Changes in signal intensity on T2WI were classified into five patterns as follows: Pattern I, lesions with three concentric zones consisting of an inner hypointense, middle hyperintense and outer hypointense zone (31 lesions); Pattern II, lesions consisting of an inner hypointense and outer hyperintense zone (4 lesions); Pattern III, lesions consisting of an inner hyperintense and outer hypointense zone (27 lesions); Pattern IV, lesions of a hyperintense area alone (2 lesions); Pattern V, lesions of a hypointense area alone (4 lesions). The outer hypointense rim in Patterns I and III is thought to represent hemosiderin deposition. The abnormal signal intensity on T2WI caused by rf ranged from 2 to 12 mm in diameter, and lesions in the late phase were smaller than lesions in the early phase. (author)