Awake versus Asleep Deep Brain Stimulation Surgery: Technical Considerations and Critical Review of the Literature

Advancements in neuroimaging have led to a trend toward direct, image-based targeting under general anesthesia without the use of microelectrode recording (MER) or intraoperative test stimulation, also referred to as “asleep” deep brain stimulation (DBS) surgery. Asleep DBS, utilizing imaging in the form of intraoperative computed tomography (iCT) or magnetic resonance imaging (iMRI), has demonstrated reliable targeting accuracy of DBS leads implanted within the globus pallidus and subthalamic nucleus while also improving clinical outcomes in patients with Parkinson’s disease. In lieu, of randomized control trials, retrospective comparisons between asleep and awake DBS with MER have shown similar short-term efficacy with the potential for decreased complications in asleep cohorts. In lieu of long-term outcome data, awake DBS using MER must demonstrate more durable outcomes with fewer stimulation-induced side effects and lead revisions in order for its use to remain justifiable; although patient-specific factors may also be used to guide the decision regarding which technique may be most appropriate and tolerable to the patient

Postoperative acute disseminated encephalomyelitis after exposure to microfibrillar collagen hemostat.

Microfibrillar collagen hemostat, known by its trade name Avitene, has been used in neurosurgery for decades. Complications with this product have been documented in other surgical specialties and described as mostly immune-mediated foreign-body reactions that can lead to a granulomatous reaction. There has never been a case of disseminated encephalomyelitis associated with this topical hemostatic agent. In this report the authors present a case of postoperative acute disseminated encephalomyelitis after exposure to Avitene. Possible pathophysiological mechanisms are discussed and the pertinent literature is reviewed

Borders of STN determined by MRI versus the electrophysiological STN. A comparison using intraoperative CT

Background It is unclear which magnetic resonance imaging (MRI) sequence most accurately corresponds with the electrophysiological subthalamic nucleus (STN) obtained during microelectrode recording (MER, MER-STN). CT/MRI fusion allows for comparison between MER-STN and the STN visualized on preoperative MRI (MRI-STN). Objective To compare dorsal and ventral STN borders as seen on 3-Tesla T2-weighted (T2) and susceptibility weighted images (SWI) with electrophysiological STN borders in deep brain stimulation (DBS) for Parkinson's disease (PD). Methods Intraoperative CT (iCT) was performed after each MER track. iCT images were merged with preoperative images using planning software. Dorsal and ventral borders of each track were determined and compared to MRI-STN borders. Differences between borders were calculated. Results A total of 125 tracks were evaluated in 45 patients. MER-STN started and ended more dorsally than respective dorsal and ventral MRI-STN borders. For dorsal borders, differences were 1.9 +/- 1.4 mm (T2) and 2.5 +/- 1.8 mm (SWI). For ventral borders, differences were 1.9 +/- 1.6 mm (T2) and 2.1 +/- 1.8 mm (SWI). Conclusions Discrepancies were found comparing borders on T2 and SWI to the electrophysiological STN. The largest border differences were found using SWI. Border differences were considerably larger than errors associated with iCT and fusion techniques. A cautious approach should be taken when relying solely on MR imaging for delineation of both clinically relevant STN border

Identification of the stria medullaris thalami using diffusion tensor imaging

Background: Deep brain stimulation (DBS) via anatomical targeting of white matter tracts defined by diffusion tensor imaging (DTI) may be a useful tool in the treatment of pathologic neurophysiologic circuits implicated in certain disease states like treatment resistant depression (TRD). We sought to determine if DTI could be used to define the stria medullaris thalami (SM), the major afferent white matter pathway to the lateral habenula (LHb), a thalamic nucleus implicated in the pathophysiology of TRD. Methods: Probabilistic DTI was performed on ten cerebral hemispheres in five patients who underwent preoperative MRI for DBS surgery. Manual identification of the LHb on axial T1 weighted MRI was used for the initial seed region for tractography. Variations in tractography depending on chosen axial slice of the LHb and chosen voxel within the LHb were also assessed. Results: In all hemispheres the SM was reliably visualized. Variations in chosen axial seed slice as well as variations in single seed placement did not lead to significant changes in SM tractography. Conclusions: Probabilistic DTI can be used to visualize the SM which may ultimately provide utility for direct anatomic targeting in DBS surgery

Accuracy of microelectrode trajectory adjustments during dbs assessed by intraoperative CT

Background/Aims: Microelectrode recording (MER)-guided deep brain stimulation (DBS) aims to place the DBS lead in the optimal electrophysiological target. When single-track MER or test stimulation yields suboptimal results, trajectory adjustments are made. The accuracy of these trajectory adjustments is unknown. Intraoperative computed tomography can visualize the microelectrode (ME) and verify ME adjustments. We aimed to determine the accuracy of ME movements in patients undergoing MER-guided DBS. Methods: Coordinates following three methods of adjustment were compared: (1) those within the default "+" configuration of the ME holder; (2) those involving rotation of the default "+" to the "x" configuration; and (3) those involving head stage adjustments. Radial error and absolute differences between coordinates were determined. Results: 87 ME movements in 59 patients were analyzed. Median (IQR) radial error was 0.59 (0.64) mm. Median (IQR) absolute x and y coordinate errors were 0.29 (0.52) and 0.38 (0.44) mm, respectively. Errors were largest after rotating the multielectrode holder to its "x"-shaped setup. Conclusion: ME trajectory adjustments can be made accurately. In a considerable number of cases, errors exceeding 1 mm were found. Adjustments from the "+" setup to the "x" setup are most prone to inaccuracies

Structural and Functional Imaging in Glioma Management.

The goal of glioma surgery is maximal safe resection in order to provide optimal tumor control and survival benefit to the patient. There are multiple imaging modalities beyond traditional contrast-enhanced magnetic resonance imaging (MRI) that have been incorporated into the preoperative workup of patients presenting with gliomas. The aim of these imaging modalities is to identify cortical and subcortical areas of eloquence, and their relationship to the lesion. In this article, multiple modalities are described with an emphasis on the underlying technology, clinical utilization, advantages, and disadvantages of each. functional MRI and its role in identifying hemispheric dominance and areas of language and motor are discussed. The nuances of magnetoencephalography and transcranial magnetic stimulation in localization of eloquent cortex are examined, as well as the role of diffusion tensor imaging in defining normal white matter tracts in glioma surgery. Lastly, we highlight the role of stimulated Raman spectroscopy in intraoperative histopathological diagnosis of tissue to guide tumor resection. Tumors may shift the normal arrangement of functional anatomy in the brain; thus, utilization of multiple modalities may be helpful in operative planning and patient counseling for successful surgery