Sequential postoperative appearance of radiofrequency pallidotomy lesions on MRI.

Abstract

We analyzed 10 radiofrequency (RF) lesions over time in 9 patients who had follow-up MRI 1 h to 43 weeks following stereotactic pallidotomies performed for medically intractable idiopathic Parkinson's disease. Pallidotomies were performed under MRI guidance, microelectrode recording, and electrical stimulation with neurological monitoring. We compared the MRI taken within 1 h after surgery for each patient to their respective follow-up MRI to determine the changes in size and signal characteristics of RF lesions over time. The postoperative follow-up MRI of RF lesions roughly fell into 4 time periods: 1 h (n = 10), 2 months (n = 3), 6 months (n = 3), and 10 months (n = 4). The average volume (+/- SD, mm3) of these lesions at each phase were as follows: 1 h = 124.35 +/- 58.48; 2 months = 50.5 +/- 30.71; 6 months = 32.36 +/- 21.07; 10 months = 53.19 +/- 28.91. The steep decline in the size of the lesion stabilizes by the 2-month period. Thereafter, the lesion size at 6 and 10 months remains stable. Eventually, the center of coagulative necrosis completely disappears, and the lesions persists as a cystic cavity. The contrast uptake of these RF lesions appears to resolve by the 6-month period. Immediate postoperative images show strong enhancement with gadolinium. There is a lesser degree of enhancement at 2 months, and no appreciable enhancement by 6 months. Interestingly, the patients with better outcome tended to have larger RF lesions. However, this difference was not statistically significant.