Pallidotomy Guided by MRI and Microrecording for Parkinson's Disease.

Lee, Kyung Jin; Son, Hyung Sun; Park, Sung Chan; Cho, Kyung Keun; Park, Hae Kwan; Choi, Chang Rak

Original Article

Journal of Korean Neurosurgical Society 2001;30(1): 41-46.

Kyung Jin Lee, Hyung Sun Son, Sung Chan Park, Kyung Keun Cho, Hae Kwan Park, Chang Rak Choi

Catholic University, Catholic Neuroscience Center, Seoul, Korea.

ABSTRACT

OBJECTIVE
The exact position of the lesion during the pallidotomy is critical to obtain the clinical improvement of parkinson's disease without damage to surrounding structure. Ventriculogrphy, CT(computed tomograpy) or MRI(magnetic resonance imaging) have been used to determine the initial coordinates of stereotactic target for pallidotomy. The goal of this study was to determine whether microelectrode recording significantly improves the neurophysiologic localization of the target obtained from MRI.
METHODS
Twenty patients were studied. They underwent a unilateral pallidotomy. Leksell frame was applied and T1 axial images parallel to the AC-PC(anterior commissure-posterior commissure) plane using a 1.5 Tesla MRI with 3mm slice thickness were obtained. Anteroposterior coordinate of target was chosen at 2mm in front of the midcommissural point and lateral coordinate between 19 and 22mm from the midline. The vertical coordinate was calculated on coronal slice using a fast spin echo inversion recovery sequence(FSEIR) related to the position of the choroidal fissure and ranged over 4-5mm below the AC-PC plane. Confirmation of the anatomical target was done on axial slices using the same FSEIR sequence. Microrecording was done at the pallidum contralateral to the symptomatic side using an electrode with a tip diameter of 1nm diameter tip and 1.1-1.4 mOhm impedance at 1000Hz. Electrophysiologic localization of the target was also confirmed intraoperatively by macrostimulation.
RESULTS
Microrecording techniques were reliable to define the transition from the base of the pallidum which was characterized by the disappearance of spike activity and by the change of the audible background activity. Signals from high amplitude neurons firing at 200-400Hz were recorded in the pallidal base. X, Y and Z coordinates of target obtained from the MRI were within 1mm from the X, Y, Z coordinates obtained with microrecording in 16 patients (80%), 15 patients(75%), 10 patients(50%) respectively. The difference of Y coordinate between on MRI and on microrecording was 4mm in only one patient.
CONCLUSION
The MRI was accurate to localize the target within 1mm of the error from microrecording target in 70% of the patients. 4mm discrepancy was observed only once. We conclude that MRI alone can be used to determine the target for pallidotomy in most patients. However, microrecording technique can still be extremely valuable in patents with aberrant anatomy or unusual MRI coordinates. We also consider physiologic confirmation of the target using macrostimulation to be mandatory in all cases.