Anterior Commissure-posterior Commissure Plane Research Articles

Improving tremor response to focused ultrasound thalamotomy.

MRI-guided high-intensity focused ultrasound thalamotomy is an incisionless therapy for essential tremor. To reduce adverse effects, the field has migrated to treating at 2 mm above the anterior commissure-posterior commissure plane. We perform MRI-guided high-intensity focused ultrasound with an advanced imaging targeting technique, four-tract tractography. Four-tract tractography uses diffusion tensor imaging to identify the critical white matter targets for tremor control, the decussating and non-decussating dentatorubrothalamic tracts, while the corticospinal tract and medial lemniscus are identified to be avoided. In some patients, four-tract tractography identified a risk of damaging the medial lemniscus or corticospinal tract if treated at 2 mm superior to the anterior commissure-posterior commissure plane. In these patients, we chose to target 1.2-1.5 mm superior to the anterior commissure-posterior commissure plane. In these patients, post-operative imaging revealed that the focused ultrasound lesion extended into the posterior subthalamic area. This study sought to determine if patients with focused ultrasound lesions that extend into the posterior subthalamic area have a differnce in tremor improvement than those without. Twenty essential tremor patients underwent MRI-guided high-intensity focused ultrasound and were retrospectively classified into two groups. Group 1 included patients with an extension of the thalamic-focused ultrasound lesion into the posterior subthalamic area. Group 2 included patients without extension of the thalamic-focused ultrasound lesion into the posterior subthalamic area. For each patient, the percent change in postural tremor, kinetic tremor and Archimedes spiral scores were calculated between baseline and a 3-month follow-up. Two-tailed Wilcoxon rank-sum tests were used to compare the improvement in tremor scores, the total number of sonications, thermal dose to achieve initial tremor response, and skull density ratio between groups. Group 1 had significantly greater postural, kinetic, and Archimedes spiral score percent improvement than Group 2 (P values: 5.41 × 10-5, 4.87 × 10-4, and 5.41 × 10-5, respectively). Group 1 also required significantly fewer total sonications to control the tremor and a significantly lower thermal dose to achieve tremor response (P values: 6.60 × 10-4 and 1.08 × 10-5, respectively). No significant group differences in skull density ratio were observed (P = 1.0). We do not advocate directly targeting the posterior subthalamic area with MRI-guided high-intensity focused ultrasound because the shape of the focused ultrasound lesion can result in a high risk of adverse effects. However, when focused ultrasound lesions naturally extend from the thalamus into the posterior subthalamic area, they provide greater tremor control than those that only involve the thalamus.

Invisible cortex sign: A highly accurate feature to localize the inferolateral central sulcus.

The central sulcus is a key landmark on MRI of the brain, but its inferolateral portion is difficult to identify if unable to trace the sulcus superoinferiorly. The authors observed that the cortex abutting the central sulcus appears isointense to the adjacent white matter on DWI, we named this the 'invisible cortex sign' and our study evaluates whether it could be used to identify the inferolateral central sulcus. Observational study of 108 consecutive 'normal' MRI studies performed from May 2016 to January 2017. A single axial DWI image - obtained in the anterior commissure-posterior commissure plane - was selected from each scan just above the subcentral gyrus such that it included the most inferolateral portion of the central sulcus. These single images were given to 10 readers (neuroradiologists, a neuroradiology fellow and radiology trainees) who marked the central sulcus based on the presence of the 'invisible cortex sign'. Their accuracy in identifying the central sulcus was compared with that of the principal investigators, who used tri-planar T1 volumetric MRI sequences. One hundred and eight consecutive patients (55 female, 53 male) were selected, ranging from 18 to 81years old (mean=40.5, σ=18.2). The central sulcus was correctly identified in 95.5% of cases (σ=3.7%; range 89.4-99.1%). The 'invisible cortex sign' is a highly accurate method of identifying the inferolateral central sulcus on a single axial DWI slice without relying on the more superior aspects of the sulcus.

EP 24. Contralateral smiles induced by deep brain stimulation of the nucleus accumbens region in a patient with major depressive disorder

Introduction Deep brain stimulation (DBS) is a well-established procedure for the treatment of therapy-refractory movement disorders. Limited evidence suggests that DBS of the nucleus accumbens region (NACC) may be effective for the treatment of psychiatric disorders, such as obsessive compulsive disorder and major depressive disorder (MDD). Hitherto, little is known concerning behavioural responses upon acute high-frequency stimulation of the NACC region in patients suffering from MDD. Objective To further characterize behavioural responses and clinical effects elicited upon acute unilateral DBS of the NACC area. Intra- and postoperative observations (including video-sequences) as well as a two-month outcome are presented. Material and Methods We performed bilateral NACC-DBS in a female patient (age: 47) with MDD refractory to psycho-, pharmaco- and electroconvulsive (>50 sessions) therapy on a compassionate-use basis. The stereotactic procedure was performed under local anaesthesia. The NACC was targeted (x) 7 mm lateral to the midline, (y) 3 mm anterior to the anterior commissure, (z) 4 mm below the anterior commissure-posterior commissure plane. A commercially available DBS lead with 4 contacts (model 3391, Medtronic Co., MN, USA; contact length: 3 mm; interelectrode distance: 4 mm) was inserted bilaterally for permanent stimulation. Results Upon test-stimulation in the operating room, acute unilateral NACC-DBS on both hemispheres stereotypically induced a visible facial reaction with a contralateral smile (bipolar stimulation of the ventralmost contacts (0− cathodal vs. 1+ anodal); pulse width: 90 μs; frequency: 130 Hz). This smile could repeatedly be elicited either when stimulation amplitude was slowly ramped up to 7 mA, or abruptly switched on to 4–5 mA. The smile was invariably associated with a significantly improved mood (as assessed by an analog scale). This effect was documented by different examiners and clearly reproducible in the subsequent clinical course. A dramatic improvement of the depression scores, patient’s mood and social behaviour was documented at a first follow-up (6 weeks postoperatively). Conclusion Albeit preliminary, the patient’s beneficial response tentatively suggests that NACC-DBS may be a viable option for selected patients with MDD. In line with previous reports on stimulation-induced smile responses in patients with obsessive compulsive disorder, our intraoperative observations support and expand the notion of the NACC area constituting or containing an important interface between limbic and motor networks, respectively, that may be involved in the pathophysiology of MDD. It is suggested that the results of long-term NACC-DBS in patients with MDD should be evaluated by larger patient samples and randomized, controlled trials.

What You See Is What You Get: Lead Location Within Deep Brain Structures Is Accurately Depicted by Stereotactic Magnetic Resonance Imaging.

Magnetic resonance imaging (MRI)-verified deep brain stimulation relies on the correct interpretation of stereotactic imaging documenting lead location in relation to visible anatomic target. However, it has been suggested that local signal distortion from the lead itself renders its depiction on MRI unreliable. To compare lead location on stereotactic MRI with subsequent location of its brain track after removal. Patients underwent deep brain stimulation with the use of MRI-guided and MRI-verified Leksell frame approach. Infection or suboptimal efficacy required lead removal and subsequent reimplantation by using the same technique. Postimplantation stereotactic MR images were analyzed. Lateral (x) and anteroposterior (y) distances from midcommissural point to center of the lead hypointensity were recorded at the anterior commissure-posterior commissure plane (pallidal electrode) or z = -4 (subthalamic electrode). Stereotactic MRI before the second procedure, x and y distances from the center of the visible lead track hypointensity to midcommissural point were independently recorded. Vectorial distance from center of the lead hypointensity to the center of its track was calculated. Sixteen electrode tracks were studied in 10 patients. Mean differences between lead artifact location and lead track location were: x coordinate 0.4 mm ± 0.2; y coordinate 0.6 mm ± 0.3. Mean vectorial distance was 0.7 mm ± 0.2. Stereotactic distance between lead location and subsequent brain track location on MRI was small. The mean discrepancy was approximately half the deep brain stimulation lead width. This suggests that lead hypointensity seen on postimplantation MRI is indeed an accurate representation of its real location within deep brain structures.

Evans' Index Revisited: The Need for an Alternative in Normal Pressure Hydrocephalus

The international guidelines for the diagnosis of normal pressure hydrocephalus (NPH) define ventricular enlargement as Evans' index greater than 0.3. To establish whether there is a correlation between Evans' index and ventricular volume (VV) in NPH and whether choosing different planes for the measurements could produce significantly different results. Pre-shunt insertion, thin-section CT scans of the brains of 10 patients with shunt-responsive NPH were reviewed retrospectively, measuring Evans' index, frontal horn index, VV, and total intracranial volume (ICV). The ventricular/intracranial volume index (VV/ICV) was calculated. Correlation between each of the linear indices and VV and VV/ICV was done. Significant differences were found in the index values calculated at different planes. The frontal horn index at a plane 16 mm parallel to the anterior commissure-posterior commissure (AC-PC) plane showed best correlation with VV and VV/ICV (r: 0.658 and 0.587, respectively). Evans' index, also obtained at a plane 16 mm parallel to the AC-PC plane, showed best correlation with VV and VV/ICV (r: 0.619 and 0.498, respectively). Evans' index value can vary significantly in a patient with NPH, depending on the level of the brain CT scan image at which the frontal horns and maximal inner skull diameters are measured. Evans' index is not an ideal method for estimating the VV in NPH patients. Volumetric measurements represent the logical accurate estimate of true ventricular size as well as the size of the other intracranial compartments.

MICROELECTRODE RECORDING IN THE POSTERIOR HYPOTHALAMIC REGION IN HUMANS

Deep brain stimulation of the posterior hypothalamic region (PHR) is an emerging technique for the treatment of medically intractable cluster headache. Few reports have analyzed single unit neuronal recordings in the human PHR. We report properties of spontaneous neuronal discharge in PHR for 6 patients who underwent DBS for cluster headaches. Initial target coordinates, determined by magnetic resonance imaging stereotactic localization, were 2 mm lateral, 3 mm posterior, and 5 mm inferior to the midpoint of the anterior commissure-posterior commissure plane. A single microelectrode penetration was performed beginning 10 mm above the anatomic target, without systemic sedation. Single units were discriminated off-line by cluster cutting in principal components space. Discharge rates, interspike intervals, and oscillatory activity were analyzed and compared between ventromedial thalamic and hypothalamic units. Six patients and 24 units were evaluated. Units in the PHR had a slow, regular spontaneous discharge with wide, low-amplitude action potentials. The mean discharge rate of hypothalamic neurons was significantly lower (mean +/- standard deviation, 13.2 +/- 12.2) than that of medial thalamic units (28.0 +/- 8.2). Oscillatory activity was not detected. Microelectrode recording in this region caused no morbidity. The single-unit discharge rate of neurons in the PHR of awake humans was 13.2 Hz and was significantly lower than medial thalamic neurons recorded dorsal to the target. The findings will be of use for microelectrode localization of the cluster headache target and for comparison with animal studies.

Stereotactic localization of the human pedunculopontine nucleus: atlas-based coordinates and validation of a magnetic resonance imaging protocol for direct localization

The pedunculopontine nucleus (PPN) is a promising new target for deep brain stimulation (DBS) in parkinsonian patients with gait disturbance and postural instability refractory to other treatment modalities. This region of the brain is unfamiliar territory to most functional neurosurgeons. This paper reviews the anatomy of the human PPN and describes novel, clinically relevant methods for the atlas-based and MRI-based localization of the nucleus. These two methods of PPN localization are evaluated and compared on stereotactic MRI data acquired from a diverse group of 12 patients undergoing implantation of deep brain electrodes at sites other than the PPN. Atlas-based coordinates of the rostral and caudal PPN poles in relation to fourth ventricular landmarks were established by amalgamating information sourced from two published human brain atlases. These landmarks were identified on acquired T1 images and atlas-derived coordinates used to plot the predicted PPN location on all 24 sides. Images acquired using a specifically modified, proton-density MRI protocol were available for each patient and were spatially fused to the T1 images. This widely available and rapid protocol provided excellent definition between gray and white matter within the region of interest. Together with an understanding of the regional anatomy, direct localization of the PPN was possible on all 24 sides. The coordinates for each directly localized nucleus were measured in relation to third and fourth ventricular landmarks. The mean (SD) of the directly localized PPN midpoints was 6.4 mm (0.5) lateral, 3.5 mm (1.0) posterior and 11.4 mm (1.2) caudal to the posterior commissure in the anterior commissure-posterior commissure plane. For the directly localized nucleus, there was similar concordance for the rostral pole of the PPN in relation to third and fourth ventricular landmarks (P>0.05). For the caudal PPN pole, fourth ventricular landmarks provided greater concordance with reference to the anteroposterior coordinate (P<0.001). There was a significant difference between localization of the PPN poles as predicted by atlas-based coordinates and direct MRI localization. This difference affected mainly the rostrocaudal coordinates; the mean lateral and anteroposterior coordinates of the directly localized PPN poles were within 0.5 mm of the atlas-based predicted values. Our findings provide simple, rapid and precise methods that are of clinical relevance to the atlas-based and direct stereotactic localization of the human PPN. Direct MRI localization may allow greater individual accuracy than that afforded by atlas-based coordinates when localizing the human PPN and may be relevant to groups evaluating the clinical role of PPN DBS.

The pyramidal tract has a predictable course through the centrum semiovale: A diffusion‐tensor based tractography study

To identify reproducible anatomical landmarks that would allow predicting the course of the pyramidal tract (PT) through centrum semiovale. A total of 20 normal volunteers (12 males, eight females) with a mean age of 34 years (range, 20-59 years) were scanned using a 1.5-Tesla clinical MR unit to assess the trajectory of the PT. Neuroanatomical characteristics of the PT passing through the centrum semiovale were assessed by two independent observers. Tractography data of 10 consecutive patients with brain tumor were used to test the precision of anatomy-based prediction of the tract location. On sagittal view, 95% of the PT depicted on tractography displayed a completely straight or primarily straight course through the supratentorial brain. In 98% of tracts, the bending point of the PT was identified < or = 3 mm from the level of the anterior commissure-posterior commissure (AC-PC) plane. In 80% of PT, the intersection with the AC-PC plane occurred midway between the AC and the PC as seen on the sagittal view. Evaluation of the PT in 10 patients with brain tumor revealed that the anatomy-based prediction of PT on the contralesional hemisphere was not substantially deviated from the actual tractography depicted PT. PT on the lesional hemispheres, however, had deviations of various degrees. The course of the PT through supratentorial brain can be predicted based on easily identifiable landmarks. This anatomy-based prediction can be clinically applied for cases without substantial mass effect from a space occupying lesion.

Safety of Anterior Commissure-Posterior Commissure-Based Target Calculation of the Subthalamic Nucleus in Functional Stereotactic Procedures

The subthalamic nucleus (STN) is a common target of functional stereotactic surgeries. High-field magnetic resonance imaging and sophisticated computer systems provide precise identification of the nucleus location in stereotactic space. However, it is unclear what additional benefit these techniques provide over traditional anterior commissure-posterior commissure (AC-PC)-based standard atlas coordinate calculation methods based on the AC-PC plane. The accuracy of AC-PC-based standard atlas coordinate targeting of the STN using 1.5-tesla images compared with direct visualization of the nucleus on fused 3-tesla images was examined. A retrospective examination of stereotactic images from 20 patients (40 STN targets) who underwent deep brain stimulation for Parkinson’s disease was undertaken at our institution. Two methods were used to identify the STN stereotactic coordinates: (1) an AC-PC-based standard atlas coordinate calculation obtained by a series of measurements using 1.5-tesla images, and (2) a computer workstation calculation using fused 3-tesla and 1.5-tesla images. Euclidean distances between two sets of coordinates of the same target were calculated in three dimensions. Differences along individual X, Y, and Z axes were analyzed to determine whether there was a greater difference in one direction than in another. Data from the right and left sides were pooled to increase the sample power. The anterior-posterior and lateral frame tilts were compared to X, Y, and Z differences to find a correlation using linear regression. Statistical analyses were performed. The accuracy of the position of the STN calculated with state-of-the-art imaging systems was not significantly better than that obtained using traditional AC-PC-based standard atlas coordinate calculation if the frame was aligned with the AC-PC plane. The mean difference was 0.45 mm, 0.72 mm, and 0.98 mm in the X, Y, and Z axes, respectively. Therefore, it is possible to effectively target the STN for stereotactic treatment of Parkinson’s disease, for instance in a situation where expensive advanced technology is unavailable.

Decreased frontal white-matter integrity in abstinent methamphetamine abusers

This study explored differences in frontal white-matter (WM) integrity between methamphetamine (MA) abusers and healthy comparison subjects using diffusion tensor imaging (DTI). Fractional anisotropy (FA) values, which indicate WM integrity, were calculated for regions-of-interest in frontal WM on diffusion tensor images of 32 MA abusers and 30 healthy comparison subjects. Frontal executive functions were also assessed by the Wisconsin Card Sorting test (WCST). MA abusers had significantly lower FA values in bilateral frontal WM at the anterior commissure-posterior commissure (AC-PC) plane and the right frontal WM 5 mm above the AC-PC plane relative to healthy comparison subjects. MA abusers had more total, perseveration and non-perseveration errors in the WCST relative to healthy comparison subjects. FA values of the right frontal WM 5 mm above the AC-PC plane negatively correlated with the number of total and non-perseveration errors in the WCST in MA abusers. In the sub-analysis for gender differences, lower FA values in frontal WM and more errors in the WCST were found only in male MA abusers, not in female MA abusers, relative to comparison subjects of the respective gender. We report that frontal WM integrity of MA abusers is compromised. This finding may also be related to impairment in frontal executive function. In addition, the neurotoxic effect of MA on frontal WM may be less prominent in women than in men, possibly due to oestrogen's neuroprotective effect.

Abnormal white matter integrity in healthy apolipoprotein E epsilon4 carriers

Apolipoprotein E epsilon4 is a major genetic risk factor for Alzheimer's disease, but the neurobiological basis for this risk is unknown. We used diffusion tensor imaging to measure diffusion anisotropy in the parahippocampal gyrus white matter in healthy elderly apolipoprotein E epsilon4 carriers and noncarriers. We also measured volumes of the lateral ventricles and temporal horns as proxies of cerebral atrophy. The epsilon4 carriers (n=14) showed significantly lower fractional anisotropy and higher radial diffusivity in the parahippocampal white matter 15 mm below the anterior commissure-posterior commissure plane than noncarriers (n=15). No group differences in ventricular volumes were found, nor were diffusion tensor imaging measures modulated by ventricular volumes. Diffusion tensor imaging may be sufficiently sensitive to detect preclinical brain changes related to Alzheimer's disease.

Reduced frontal white matter integrity in Early-Onset schizophrenia: a preliminary study

BackgroundResearch suggests that brain frontal white matter (WM) might be qualitatively altered in adolescents with early onset schizophrenia (EOS). Diffusion tensor imaging provides a relatively new approach for quantifying possible connectivity of WM in vivo. MethodsDiffusion tensor imaging was used to examine the WM integrity of frontal regions at seven levels from 25 mm above to 5 mm below the anterior commissure–posterior commissure (AC-PC) plane. Three other regions were examined: the occipital region at the AC-PC plane and the genu and splenium of the corpus callosum. Fractional anisotropy was compared between 12 adolescents (nine male, 3 female) with EOS (onset of psychotic symptoms by age 18 years) and nine age-similar healthy comparison subjects (six male, 3 female). ResultsAdolescents with EOS had significantly reduced fractional anisotropy in the frontal WM at the AC-PC plane in both hemispheres and in the occipital WM at the AC-PC plane in the right hemisphere. ConclusionsThese preliminary data support a hypothesis that alterations in brain WM integrity occur in adolescents with EOS. Abnormalities found in this study were similar to those reported in adults with chronic schizophrenia. Additional studies are needed to assess whether there is progression of WM abnormalities in schizophrenia.

Frontal white matter microstructure and treatment response of late-life depression: a preliminary study.

This study tested the hypothesis that microstructural abnormalities in white matter areas of the brain containing frontostriatal tracts are associated with a low rate of remission of geriatric depression. Thirteen older patients with major depression received open, but controlled, treatment with citalopram at a target daily dose of 40 mg for 12 weeks. Diffusion tensor imaging was used to determine fractional anisotropy in preselected white matter regions. Survival analysis with Cox's proportional hazards model revealed that lower fractional anisotropy of the right and the left frontal white matter regions 15 mm above the anterior commissure-posterior commissure plane was associated with a low remission rate after age was considered. Remission was not significantly associated with fractional anisotropy of lower frontal regions or a temporal region. Microstructural white matter abnormalities lateral to the anterior cingulate may be associated with a low rate of remission of geriatric depression.

Reduced frontal white matter integrity in cocaine dependence: a controlled diffusion tensor imaging study

Background: In vivo magnetic resonance studies have found that cocaine dependence is associated with T2 signal hyperintensities and metabolite abnormalities in cerebral white matter (WM). Functional neuroimaging studies have suggested that chronic cocaine use is primarily associated with frontal lobe deficits in regional cerebral blood flow and brain glucose metabolism levels; however, the effects of cocaine dependence, if any, on frontal WM microstructure are unknown. Thus, we sought to examine the effects of cocaine dependence on frontal WM integrity. Methods: Diffusion tensor imaging was employed to examine the WM integrity of frontal regions at four levels: 10 mm above, 5 mm above, 0 mm above, and 5 mm below the anterior commissure-posterior commissure (AC-PC) plane. The fractional anisotropy (FA) of 12 cocaine-dependent patients and 13 age-similar control subjects was compared. Results: The cocaine-dependent patients had significantly reduced FA in the frontal WM at the AC-PC plane and a trend toward reduced FA at 5 mm below the AC-PC plane, suggestive of reduced WM integrity in these regions. Conclusions: These findings were consistent with the hypothesis that cocaine dependence involves alterations in orbitofrontal connectivity, which may be involved in the decision-making deficits seen in this disorder.