Evaluation of Thalamic and Subthalamic Surgical Lesions in the Alleviation of Parkinson's Disease

THOUGH most attention in the surgical treatment of Parkinson's disease has been focused on nuclear regions in the lateral floor of the thalamus, 5,6,1~ a small minority of stereotaxic surgeons have made lesions in subthalamic structures. Exploration of specific subthalamic areas has been made possible by improved instrumentation, including the smaller electrodes and more precise apparatus for depth-recording and stimulation. The most commonly used operations have been Spiegel's campotomy in the H fields of Forel, 17-21 Meyers' approach to the substantia nigra, 1~6 and Andy's subthalotomy? Other surgeons have placed lesions in a position that produces a zone of destruction m the ventro-oral thalamus and the subthalamic fiber tracts immediately below. Thus, Van Buren 22-24 directs the electrode tip to a target 2 mm below the intercommissural line; Bertrand 2-4 passes the electrode through the nucleus ventralis posterolateralis and extends the lesion into the subthalamic area immediately below this nucleus; and Kjellberg n introduces the electrode in a horizontal plane so that a lesion is produced on the floor of the thalamus itself. It has been suggested that a small surgical lesion in the network of fiber tracts composing H1 or H2 or in field H might be less hazardous and just as effective as a large lesion in the thalamus. During the past 4 years at the Lahey Clinic, a small radiofrequency electrode has been carried to the surgical target by the McPherson stereotaxic instrument. The noninsulated tip of the electrode measures 5 • 1.1 mm and contains a thermistor to monitor the degree of heat generated. The danger of hemorrhage has been virtually eliminated by temperatures of 70 ~ to 75~ in an electrode tip of this size. The size of the lesion can be enlarged by varying the time factor f rom 2 to 6 minutes. The largest area of destruction has been an 8 to 9 mm sphere, the smallest ap-