Pre- and postoperative MR evaluation of stereotactic pallidotomy

Stereotactic pallidotomy, which has evolved as a result of technological advances in high-resolution MR imaging and microelectrode electrophysiological recording, is becoming a major form of treatment for patients with Parkinson disease in whom medical therapy has failed. We describe the location and appearance of the pallidotomy lesion on high-resolution MR images. MR images in 83 patients (60 men and 23 women) who underwent stereotactic pallidotomy were reviewed retrospectively. The prepallidotomy screening study included standard spin-echo and gradient-echo sequences. After placement of a stereotactic headframe, volume-acquisition T1-weighted spoiled gradient-echo images were acquired for target localization in the posteroventral internal globus pallidus. One to three days after the pallidotomy, volume-acquisition T1-weighted and standard spin-echo sequences were obtained. In 16 patients, turbo spin-echo inversion recovery images also were obtained before and after surgery. The diameter, signal intensity, and location of the lesions relative to the midcommissural point and the intercommissural line were noted. The average lesion volume was 118 mm3 while that of the lesion-edema complex was 420 mm3. The midportion of the lesion was located on average 3.5 mm anterior to the midcommissural point, 21 mm lateral to the middle of the third ventricle, and 1.2 mm inferior to the intercommissural line. Signal intensity of the lesions varied, but all had a rim of edema. Forty-two patients had edema extending into the optic tract, four had increased signal in the ipsilateral basal ganglia on T2-weighted images, and seven had hemorrhage involving the ipsilateral caudate, internal capsule, and putamen. All patients experienced some improvement in contralateral bradykinesia, rigidity, and dystonia. The acute pallidotomy lesion is invariably located within the posteroventral internal globus pallidus, is usually hyperintense centrally on T1-weighted and turbo spin-echo inversion recovery MR images, and has a thin rim of edema. Edema extending into the ipsilateral optic tract was a common finding, but this series of patients evinced no visual changes.