Neurosurgery Blog

Acta Neurochir (2011) 153:2307–2318. DOI 10.1007/s00701-011-1081-7

The aim of our study was to evaluate discrepancies between the electrophysiologically and MRI-defined subthalamic nucleus (STN) in order to contribute to the ongoing debate of whether or not microelectrode recording (MER) provides additional information to imageguided targeting in deep brain stimulation.

Methods: Forty-four STNs in 22 patients with Parkinson’s disease were investigated. The three-dimensional MRI-defined STN was derived from segmentations of axial and coronal T2-weighted images. The electrophysiological STNs were generated from intraoperative MERs in 1,487 locations. The stereotactical coordinates of positive and negative STN recordings were re-imported to the planning software, where a three-dimensional reconstruction of the electrophysiological STN was performed and fused to the MRI data set. The estimated borders of the MRI- and MERSTN were compared. For statistical analysis Student’s t, Mann-Whitney rank sum and Fisher’s exact tests were used.

Results: MER-STN volumes, which were found outside the MRI-STN, ranged from 0 mm3 to 87 mm3 (mean: 45 mm3). A mean of 44% of the MER-STN volumes exceeded the MRI-STN (maximum: 85.1%; minimum: 15.1 %); 53.4% (n=793) of the microelectrode recordings were concordant and 46.6% (n=694) discordant with the MRI-defined anatomical STN. Regarding the dorsal borders, we found discrepancies between the MER- and MRI-STN of 0.27 mm (= mean; SD: 0.51 mm) on the first operated side and 1.51 mm (SD: 1.5 mm) on the second (p=0.010, t-test).

Conclusions: MER provides additional information to highresolution anatomical MR images and may help to detect the amount and direction of brain shift.

J Neurosurg 113:639–647, 2010.DOI: 10.3171/2010.3.JNS091385

A challenge associated with deep brain stimulation (DBS) in treating advanced Parkinson disease (PD) is the direct visualization of brain nuclei, which often involves indirect approximations of stereotactic targets. In the present study, the authors compared T2*-weighted images obtained using 7-T MR imaging with those obtained using 1.5- and 3-T MR imaging to ascertain whether 7-T imaging enables better visualization of targets for DBS in PD.

Methods. The authors compared 1.5-, 3-, and 7-T MR images obtained in 11 healthy volunteers and 1 patient with PD.

Results. With 7-T imaging, distinct images of the brain were obtained, including the subthalamic nucleus (STN) and internal globus pallidus (GPi). Compared with the 1.5- and 3-T MR images of the STN and GPi, the 7-T MR images showed marked improvements in spatial resolution, tissue contrast, and signal-to-noise ratio.

Conclusions. Data in this study reveal the superiority of 7-T MR imaging for visualizing structures targeted for DBS in the management of PD. This finding suggests that by enabling the direct visualization of neural structures of interest, 7-T MR imaging could be a valuable aid in neurosurgical procedures.

J Neurosurg 112:1283–1288, 2010.DOI: 10.3171/2009.10.JNS09917

Parkinson disease (PD) is often accompanied by various postural abnormalities such as camptocormia (bent spine) or Pisa syndrome (lateral flexion). The authors studied the effect of subthalamic nucleus deep brain stimulation (STN DBS) on postural abnormality in patients with PD.

Methods. The authors retrospectively reviewed the clinical course of 18 patients who suffered from significant postural abnormality and underwent bilateral STN DBS. Patients whose preoperative posture score (Unified Parkinson’s Disease Rating Scale III, item 28) was 2 or more in the “medication-on” state were enrolled in this study. Eight patients were considered to have camptocormia, and 10 patients were considered to have so-called Pisa syndrome. Nine patients showed apparent thoracolumbar spinal deformity on radiography. Most patients had significant motor fluctuations from levodopa.

Results. In 13 patients with moderate postural abnormality (score of 2 on item 28), 9 patients improved soon after surgery, but 1 patient relapsed. Two patients improved gradually over a long period after surgery, whereas 2 patients did not improve at all. In 5 patients with severe postural abnormality (score of 3 or 4 on item 28), 2 patients improved slightly in the long-term follow-up period after surgery, but 3 patients did not improve at all.

Conclusions. Postural abnormality in patients with PD could be ameliorated by STN DBS, and therefore surgery should be considered before irreversible spinal deformity develops

J Neurosurg 112:479–490, 2010. DOI: 10.3171/2009.6.JNS081161

The authors discuss their method for placement of deep brain stimulation (DBS) electrodes using interventional MR (iMR) imaging and report on the accuracy of the technique, its initial clinical efficacy, and associated complications in a consecutive series of subthalamic nucleus (STN) DBS implants to treat Parkinson disease (PD).

Methods. A skull-mounted aiming device (Medtronic NexFrame) was used in conjunction with real-time MR imaging (Philips Intera 1.5T). Preoperative imaging, DBS implantation, and postimplantation MR imaging were integrated into a single procedure performed with the patient in a state of general anesthesia. Accuracy of implantation was assessed using 2 types of measurements: the “radial error,” defined as the scalar distance between the location of the intended target and the actual location of the guidance sheath in the axial plane 4 mm inferior to the commissures, and the “tip error,” defined as the vector distance between the expected anterior commissure–posterior commissure (AC-PC) coordinates of the permanent DBS lead tip and the actual AC-PC coordinates of the lead tip. Clinical out- come was assessed using the Unified Parkinson’s Disease Rating Scale part III (UPDRS III), in the off-medication

state.Results. Twenty-nine patients with PD underwent iMR imaging–guided placement of 53 DBS electrodes into the STN. The mean (± SD) radial error was 1.2 ± 0.65 mm, and the mean absolute tip error was 2.2 ± 0.92 mm. The tip error was significantly smaller than for STN DBS electrodes implanted using traditional frame-based stereotaxy (3.1 ± 1.41 mm). Eighty-seven percent of leads were placed with a single brain penetration. No hematomas were visible on MR images. Two device infections occurred early in the series. In bilaterally implanted patients, the mean improvement on the UPDRS III at 9 months postimplantation was 60%.

Conclusions. The authors’ technical approach to placement of DBS electrodes adapts the procedure to a standard configuration 1.5-T diagnostic MR imaging scanner in a radiology suite. This method simplifies DBS implantation by eliminating the use of the traditional stereotactic frame and the subsequent requirement for registration of the brain in stereotactic space and the need for physiological recording and patient cooperation. This method has improved accuracy compared with that of anatomical guidance using standard frame-based stereotaxy in conjunction with pre- operative MR imaging.

Philip A. Starr, MD, Alastair J.Martin, PhD, Paul S. Larson, MD

Neurosurgery Clinics of North America

Volume 20, Issue 2, Pages 207-217 (April 2009)

The authors describe a method for placement of deep brain stimulator electrodes using interventional MRI in conjunction with a skull-mounted aiming device (Medtronic Nexframe). This approach adapts the procedure to a standard-configuration 1.5-T diagnostic MRI scanner in a radiology suite. Preoperative imaging, device implantation, and postimplantation MRI are integrated into a single procedure performed under general anesthesia, providing real-time, high-resolution magnetic resonance confirmation of electrode position. The method is conceptually simpler than the current standard technique for deep brain stimulator placement, as it eliminates the stereotactic frame, the subsequent requirement for registration of the brain in stereotactic space, physiologic testing, and the need for patient cooperation. With further technical refinement, the interventional MRI method should improve the accuracy, safety, and speed of deep brain stimulator electrode placement.