Ryan B. Kochanski

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.

Use of intraoperative CT to predict the accuracy of microelectrode recording during deep brain stimulation surgery. A proof of concept study.

OBJECTIVES Intraoperative computed tomography (iCT) is currently used to confirm the target location of the microelectrode (ME) during microelectrode recording (MER) and ultimate location of deep brain stimulation (DBS) leads at our institution. We evaluated whether iCT can be used to predict the trajectory and accuracy of the ME track. PATIENTS AND METHODS Intraoperative imaging profiles of ten consecutive patients who had undergone DBS surgery were retrospectively reviewed. We found that cranial iCT, in addition to visualizing the target, also visualizes the extra-cranial segment of the guide tube (ECGT) used to insert the ME. We propose a hypothetical technique that extrapolates the trajectory of only the ECGT down to target depth using planning software. In order to provide a proof of concept analysis of this hypothetical technique, we retrospectively assessed post MER placement iCT studies and used planning software to visualize only the ECGT. An extrapolated vector was drawn along the long axis of the ECGT down to the same depth (z) as the ME. The obtained x and y coordinates were subsequently recorded and compared to the x and y coordinates of the ME tip to validate this technique. RESULTS The average radial error between ECGT trajectory coordinates and final ME tip coordinates was 0.93±0.1mm (mean±SEM). CONCLUSION The use of iCT to predict accuracy of microelectrode location is feasible. In the future, performing iCT before guide tube penetration of dura can allow for trajectory prediction and if needed, correction of the ME, thereby potentially improving accuracy and reducing the number of MER tracks.

Improving the accuracy of microelectrode recording in deep brain stimulation surgery with intraoperative CT

Microelectrode recording (MER) is used to confirm electrophysiological signals within intended anatomic targets during deep brain stimulation (DBS) surgery. We describe a novel technique called intraoperative CT-guided extrapolation (iCTE) to predict the intended microelectrode trajectory and, if necessary, make corrections in real-time before dural opening. Prior to dural opening, a guide tube was inserted through the headstage and rested on dura. Intraoperative CT (iCT) was obtained, and a trajectory was extrapolated along the path of the guide tube to target depth using targeting software. The coordinates were recorded and compared to initial plan coordinates. If needed, adjustments were made using the headstage to correct for error. The guide tube was then inserted and MER ensued. At target, iCT was performed and microelectrode tip coordinates were compared with planned/adjusted track coordinates. Radial error between MER track and planned/adjusted track was calculated. For comparison, MER track error prior to the iCTE technique was assessed retrospectively in patients who underwent MER using iCT, whereby iCT was performed following completion of the first MER track. Forty-seven MER tracks were analyzed prior to iCTE (pre-iCTE), and 90 tracks were performed using the iCTE technique. There was no difference between radial error of pre-iCTE MER track and planned trajectory (2.1±0.12mm) compared to iCTE predicted trajectory and planned trajectory (1.76±0.13mm, p>0.05). iCTE was used to make trajectory adjustments which reduced radial error between the newly corrected and final microelectrode tip coordinates to 0.84±0.08mm (p<0.001). Inter-rater reliability was also tested using a second blinded measurement reviewer which showed no difference between predicted and planned MER track error (p=0.53). iCTE can predict and reduce trajectory error for microelectrode placement compared with the traditional use of iCT post MER.

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.

A rare intracranial tumor consisting of malignant anaplastic and papillary meningioma subtypes.

Background: Intracranial tumors with heterogeneous histopathology are a well-described pathologic entity. Pathologically, distinct tumors in direct contact with one another, also known as collision tumors are exceptionally rare, and collision between meningioma subtypes has not been previously described in the literature. Case Description: A 79-year-old female with a history of breast carcinoma presenting with visual and motor deficits and imaging/intraoperative findings consistent with separate, distinct lesions. Histopathologic findings provided evidence for a collision between World Health Organization Grade III anaplastic and papillary meningioma. Conclusion: We report a possible collision tumor between two separate meningioma subtypes based on the unique radiologic, intraoperative, and histopathologic findings. Submission of multiple pathologic specimens during surgical resection is key for accurate histopathologic diagnosis.

Amygdalohippocampectomy for epilepsy in a patient with prior ipsilateral deep brain stimulator lead placement.

In light of failed medical therapy for movement disorders, the use of deep brain stimulation (DBS) has increased the last two decades. Many complications may transpire; however, to our knowledge, the literature does not mention the phenomena of brain shift from a second unrelated neurosurgical procedure and its theoretical effect on lead displacement and lead function. We present a patient with a left sided DBS for essential tremor and subsequent left amygdalohippocampectomy for temporal lobe epilepsy with minimal radiographic distortion of the DBS lead and without clinical or functional complications. A 47-year-old woman presented with bitemporal epilepsy secondary to a brain injury acquired in childhood in addition to a comorbid bilateral essential tremor, both refractory to medical intervention. A successful left-sided DBS placement was performed with satisfactory resolution of her essential tremor. The patient subsequently developed deterioration of seizure control, becoming refractory to anti-epileptic medications, requiring surgical intervention. A left-sided selective amygdalohippocampectomy and techniques to minimize brain shift were performed without complications. Postoperative imaging suggested minimal distortion of the DBS lead. This did not correspond with reemergence of her essential tremor, implying that the lead maintained functional utility. Brain shift secondary to a craniotomy may cause DBS lead displacement. This phenomenon should be considered when planning operative approaches and can be limited by selective resections. With the growing propensity for placement of DBS leads and the risk of lead displacement, it is important to consider operative approaches to minimize brain shift.

Prevalence and Impact of Left-Handedness in Neurosurgery

BACKGROUND Approximately 10%-13% of the population is left-handed (LH), and certain professions have varied representation of LH individuals. LH surgeons must overcome unique difficulties owing to the right-handed (RH) operative environment. This study assesses prevalence and impact of left-handedness on training and operative experience of neurosurgeons. METHODS An e-mail survey was designed and sent to 5109 U.S. neurosurgeons and neurosurgical trainees. The survey was completed by 1482 responders (29.0% response rate). RESULTS Of respondents, 252 (17.0%) reported being LH. LH neurosurgeons were more likely than RH neurosurgeons to report ambidexterity in the operating room (36.5% vs. 13.3%, P < 0.001). During neurosurgical training, 23.5% of RH trainers addressed LH-specific issues compared with 44.7% of LH trainers. LH trainers were more likely to describe LH trainees as having greater technical ability (18.9%). Most trainers reported equal comfort teaching LH and RH trainees. LH trainees reported difficulties with RH surgical tools (42.7%) and a tendency to alter handedness for surgery (62.7%). The impact of these areas lessens in LH attendings (27.8% and 39.9%, respectively). Most LH neurosurgeons denied specific training for left-handedness and access to LH-specific tools, and 24.0% of LH trainees reported feeling disadvantaged owing to their handedness. CONCLUSIONS LH neurosurgeons may be overrepresented in neurosurgery, yet handedness is rarely addressed in neurosurgical training. Despite this, there is evidence of some degree of adaptation through training. There may be some benefit from recognizing differences in handedness in the operating room and attempting to give access for LH-specific mentorship during training.

Repair of Temporal Bone Defects via the Middle Cranial Fossa Approach: Treatment of 2 Pathologies With 1 Operation

BACKGROUND Temporal bone dehiscence (TBD) often results in leakage of cerebrospinal fluid (CSF) and/or encephalocele. TBD can also occur over the superior semicircular canal, causing debilitating vertigo. Both can be repaired surgically, but traditional treatment is focused only on one pathology, not both. OBJECTIVE To report our experience in the treatment of TBD via the middle cranial fossa (MCF) approach. METHODS A retrospective review was conducted for all patients who underwent MCF approach for surgical repair of any temporal fossa dehiscence. RESULTS A total of 34 patients underwent a total of 37 surgeries. Obesity was prevalent; 21 patients (61.8%) were obese (BMI [body mass index] > 30 kg/m2), and 7 (20.6%) were overweight (BMI 25-30 kg/m2). The most common presenting symptom was hearing disturbance (70.3%), followed by otorrhea (51.4%). Empty sella was noted on computed tomography or magnetic resonance imaging in 15 patients (45.5%). Eight of the 34 patients (23.5%) were found to have superior semicircular canal dehiscence (SCD). Hearing improved with surgical intervention in 25 of 26 patients with hearing loss as a presenting symptom (96%). CSF resolved in 18 of 19 cases (95%). Seventy-three percent of patients reported at least minimal improvement in vertigo. CONCLUSION TBD may present with symptoms of CSF leak/encephalocele, but may also present with superior SCD. We recommend consistent review of the temporal bone imaging to check for superior SCD, and repair of the SCD first to prevent complications involving the labyrinth and cochlea. MCF approach using a multilayer repair without a lumbar drain is highly effective with minimal risk of complications.

S64. Analysis of beta frequency oscillations in recorded local field potentials of Parkinson’s disease patients undergoing deep brain stimulation

Introduction Local field potential (LFP) recordings from implanted deep brain stimulator (DBS) leads can provide insight into the pathogenesis of the Parkinson’s disease (PD) specifically by looking at some of the local network properties at the location of the electrode. We recorded LFP activity from DBE leads implanted in the subthalamic nucleus (STN) and performed subsequent data analysis on PD patients undergoing DBS surgery in the off state both at rest and during continuous movement of the contralateral hand in order to identify any reproducible pathophysiological signatures of the disease. Methods LFPs were recorded in 8 patients with PD who underwent bilateral DBS lead implantation within the STN. Following DBS lead placement, bipolar (0–1, 1–2, 2–3) recordings were performed for 2 min at rest and another 2 min with contralateral repetitive hand grasp movements. All recordings were performed in the off state with at least 12 h of since their last medication and prior to macrostimulation testing in the nucleus. The raw LFP recordings were transformed to the frequency domain via the fast fourier transform and then a power spectral was generated from that data with a frequency resolution of 1.3 Hz. Beta-band spectral peaks were located and compared between the two testing states. Results In all patients, predominance of both low and high beta band frequencies (13–20 and 20–35 Hz respectively) were observed both at rest and during movement at the DBS contact where stimulation was deemed to be most therapeutic. Paradoxically, stronger beta peak energy was noted during movement as opposed to the rest state in all patients. Conclusion In patients with PD, excess beta band coupling that paradoxically synchronizes with movement may be a signature of the off state. This excess beta band activity appears to also correlate with the most active DBS lead contact. This increase in energy, or synchronization, during the movement phase is in contrast to what happens in the cortex during similar EEG analysis. This increase in the abnormal beta energy, in PD patients, may help explain the abnormal movements, such as rigidity and bradykinesia, seen in these patients. Further investigations may to help to identify and provide stimulation in situations where excess beta band activity is prevalent at the active contact.