TECHNIQUE OF STEREOTAXIC MEDIAL THALAMOTOMY WITH THE LEKSELL GAMMA-KNIFE FOR TREATMENT OF CHRONIC PAIN

Nineteen patients underwent a total of 24 medial thalamic lesions made with the Leksell Gamma Knife for the treatment of chronic intractable pain after extensive prior medical and surgical intervention had fail ed to provide pain relief. The lesion locations were based on prior ex perience with open radiofrequency medial thalamotomies for the treatme nt of pain and were directed at the intralaminar, mediodorsal, centrom edian, and parafascicular nuclei. All lesions were made with the 4 mm collimator helmet at radiosurgical doses from 140-180 Gray. Follow-up MRI scans indicated anatomically distinct lesions which developed 3-6 weeks after the procedure and were fully formed by 8-12 weeks. The les ion volumes averaged 300-400 mm(3) for a single isocentre, 600-900 mm( 3) for two isocentres, and 900-1100 mm(3) for three isocentres. One pa tient developed a lesion 5500 mm(3) in volume after a two isocentre le sion at 160 Gray. Of 15 patients who have been followed for more than 3 months (average follow-up 12 months) four patients (27%) are virtual ly pain free and functioning normally, whereas five other patients (33 %) achieved greater than 50% pain relief. Thus 9/15 patients (60%) hav e had worthwhile benefit from medial thalamotomy with the Gamma Knife. Medial thalamotomy with the Gamma Knife produces thalamic lesions whi ch are reliable in size, shape and location with a low complication ra te and offers a minimally invasive, cost effective treatment for certa in selected patients with chronic intractable pain.