Variability in lesion location after microelectrode-guided pallidotomy forParkinson's disease: anatomical, physiological, and technical factors thatdetermine lesion distribution

Object. To understand the factors that determine the distribution of lesion s after microelectrode-guided pallidotomy for Parkinson's disease, the auth ors quantitatively characterized lesion location in a cohort of patients wh o were prospectively followed to determine the effects of pallidotomy on cl inical outcome. Methods. Thirty-three patients underwent volumetric magnetic resonance (MR) imaging after surgery to allow quantitative lesion localization in relatio n to conventional intraventricular landmarks and, alternatively, more anato mically relevant landmarks. The validity of the method was verified in a co hort of postpallidotomy patients who underwent concurrent volumetric and st ereotactic MR imaging in an external head frame. Lesions were distributed o ver a considerable distance in the anteroposterior (8.8 mm) and mediolatera l (8.7 mm) dimensions in relation to the anterior commissure and wall of th e third ventricle, respectively. Less variation was seen in lesion location in the dorsoventral dimension (4.8 mm) in relation to the intercommissural plane. Conclusions. Lesion distribution was not random: lesion locations in the an teroposterior and mediolateral dimensions were highly correlated, such that lesions were distributed from anteromedial to posterolateral, parallel to the border of the globus pallidus internus with the obliquely oriented inte rnal capsule. The factors that led to variability in lesion location were v ariation in third ventricle width and the oblique anteromedial-to-posterola teral course of the internal capsule. This demonstration of variability of lesion location in a cohort of patients who experienced excellent clinical benefits and minimal postoperative complications emphasizes the importance of anatomical variations in determining lesion position and the need for ph ysiological corroboration for correct lesion placement.