N contemporary stereotactic functional neurosurgery for movement disorders, mapping of the basal ganglia is based on localizing the AC and PC, determining the functional targets using the Schaltenbrand and Wahren Atlas, 7 and identifying the neural structure using the electrophysiological method. For a visualization of the AC-PC line, ventriculography is considered the gold standard and is still used in some medical centers. Recently, the use of intraoperative ventriculography has decreased and is being replaced by MR imaging for preoperative target localization. Magnetic resonance imaging is superior to CT scanning in the resolution of reconstructed images and in the identification of landmark structures. Moreover, imageguided neurosurgical planning software with the aid of MR images can correct the slight tilting and rotation of the head within the stereotactic headframe, which cannot be corrected in ventriculography. Functional targets have been indirectly localized by calculations based on the coordinates of AC and PC with CT or MR images, or directly visualized with MR imaging. 1,10 However, it should be noted that the information on MR imaging concerning the patient's condition is obtained before surgery, whereas ventriculography provides the information after the bur hole opening. Therefore, even if the brain is shifted for any reason during surgery, ventriculography can update the real-time position of the AC and PC. The efficacy in stereotactic surgery for movement disorders depends on accurate lesioning or electrode positioning, as well as localizing the neural structure anatomically and physiologically ideal for each symptom. In 1975 Gerdes et al. 3 first described the error resulting from subdural air invasion and "brain sinking" in the stereotactic procedure. It is empirically known that an intracranial air invasion and CSF outflow are associated with brain sinking during surgery; however, authors of few studies have shown the ef- Object. The goal of this study was to focus on the tendency of brain shift during stereotactic neurosurgery and the shift's impact on the unilateral and bilateral implantation of electrodes for deep brain stimulation (DBS). Methods. Eight unilateral and 10 bilateral DBS electrodes at 10 nuclei ventrales intermedii and 18 subthalamic nuclei were implanted in patients at Kaizuka Hospital with the aid of magnetic resonance (MR) imaging-guided and microelectrode-guided methods. Brain shift was assessed as changes in the 3D coordinates of the anterior and posterior commissures (AC and PC) with MR images before and immediately after the implantation surgery. The positions of the implanted electrodes, based on the midcommissural point and AC-PC line, were measured both on x-ray films (virtual position) during surgery and the postoperative MR images (actual position) obtained on the 7th day postoperatively. Results. Contralateral and posterior shift of the AC and PC were the characteristics of unilateral and bilateral procedures, respectively. The authors suggest the following. 1) The first unilateral procedure elicits a unilateral air invasion, resulting in a contralateral brain shift. 2) During the second procedure in the bilateral surgery, the contralateral shift is reset to the midline and, at the same time, the anteroposterior support by the contralateral hemisphere against gravity is lost due to a bilateral air invasion, resulting in a significant posterior (caudal) shift. Conclusions. To note the tendency of the brain to shift is very important for accurate implantation of a DBS electrode or high frequency thermocoagulation, as well as for the prediction of therapeutic and adverse effects of stereotactic surgery.
Miyagi et al. REF studied both unilateral and bilateral implantations and concluded on the brain shift tendency for both type of procedures.
Brain shift: an error factor during implantation of deep brain stimulation electrodes.
Journal of neurosurgery
Journal of neurosurgery
Medicine