Input-output relation of midbrain connectomics in a rodent model of depression

BACKGROUND

The symptoms associated with depression are believed to arise from disruptions in information processing across brain networks. The ventral tegmental area (VTA) influences reward-based behavior, motivation, addiction, and psychiatric disorders, including depression. Deep brain stimulation (DBS) of the medial forebrain bundle (MFB), is an emerging therapy for treatment-resistant depression. Understanding the depression associated anatomical networks crucial for comprehending its antidepressant effects.

METHODS

Flinders Sensitive Line (FSL), a rodent model of depression and Sprague-Dawley rats (n = 10 each) were used in this study. We used monosynaptic tracing to map inputs of VTA efferent neurons: VTA-to-NAc nucleus accumbens (NAc) (both core and shell) and VTA-to-prefrontal cortex (PFC). Quantitative analysis explored afferent diversity and strengths.

RESULTS

VTA efferent neurons receive a variety of afferents with varying input weights and predominant neuromodulatory representation. Notably, NAc-core projecting VTA neurons showed stronger afferents from dorsal raphe, while NAc shell-projecting VTA neurons displayed lower input strengths from cortex, thalamus, zona incerta and pretectal area in FSL rats. NAc shell-projecting VTA neurons showed the most difference in connectivity across the experimental groups.

LIMITATIONS

Lack of functional properties of the anatomical connections is the major limitation of this study. Incomplete labeling and the cytotoxicity of the rabies virus should be made aware of.

CONCLUSIONS

These findings provide the first characterization of inputs to different VTA ascending projection neurons, shedding light on critical differences in the connectome of the midbrain-forebrain system. Moreover, these differences support potential network effects of these circuits in the context of MFB DBS neuromodulation for depression.

Deep brain stimulation electrodes may rotate after implantation-an animal study

Directional deep brain stimulation (dDBS) electrodes allow to steer the electrical field in a specific direction. When implanted with torque, they may rotate for a certain time after implantation. The aim of this study was to evaluate whether and to which degree leads rotate in the first 24 h after implantation using a sheep brain model. dDBS electrodes were implanted in 14 sheep heads and 3D rotational fluoroscopy (3D-RF) scans were acquired to visualize the orientation of the electrode leads. Electrode leads were clockwise rotated just above the burr holes (180° n = 6, 360° n = 6, 2 controls) and 3D-RF scans were again acquired after 3, 6, 13, 17, and 24 h, respectively. One hundred eighty degree rotated electrodes showed an initial rotation of 83.5° (range: 35.4°-128.3°) and a rotation of 114.0° (range: 57°-162°) after 24 h. With 360° torsion, mean initial rotation was 201° (range: 3.3°-321.4°) and mean rotation after 24 h 215.7° (range 31.9°-334.7°), respectively. Direct postoperative imaging may not be accurate for determining the rotation of dDBS electrodes if torque is present.

Ventral tegmental area connections to motor and sensory cortical fields in humans

In humans, sensorimotor cortical areas receive relevant dopaminergic innervation—although an anatomic description of the underlying fiber projections is lacking so far. In general, dopaminergic projections towards the cortex originate within the ventral tegmental area (VTA) and are organized in a meso-cortico-limbic system. Using a DTI-based global tractography approach, we recently characterized the superolateral branch of the medial forebrain bundle (slMFB), a prominent pathway providing dopaminergic (and other transmitters) innervation for the pre-frontal cortex (Coenen et al., NeuroImage Clin 18:770–783, 2018). To define the connections between VTA and sensory–motor cortical fields that should contain dopaminergic fibers, we use the slMFB as a key structure to lead our fiber selection procedure: using a similar tracking-seed and tractography algorithm, we describe a dorsal extension of this slMFB that covers sensorimotor fields that are dorsally appended to pre-frontal cortical areas. This “motorMFB”, that connects the VTA to sensorimotor cortical fields, can be further segregated into three sub-bundles with a seed-based fiber-selection strategy: A PFC bundle that is attendant to the pre-frontal cortex, passes the lateral VTA, runs through the border zone between the posterior and lateral ventral thalamic nucleus, and involves the pre- and postcentral gyrus. An MB bundle that is attendant to the mammillary bodies runs directly through the medial VTA, passes the lateral ventral thalamic nucleus, and involves the pre- and postcentral gyrus as well as the supplementary motor area (SMA) and the dorsal premotor cortex (dPMC). Finally, a BC bundle that is attendant to the brainstem and cerebellum runs through the lateral VTA, passes the anterior ventral thalamic nucleus, and covers the SMA, pre-SMA, and the dPMC. We, furthermore, included a fiber tracking of the well-defined dentato-rubro-thalamic tract (DRT) that is known to lie in close proximity with respect to fiber orientation and projection areas. As expected, the tract is characterized by a decussation at the ponto-mesencephal level and a projection covering the superior-frontal and precentral cortex. In addition to the physiological role of these particular bundles, the physiological and pathophysiological impact of dopaminergic signaling within sensorimotor cortical fields becomes discussed. However, some limitations have to be taken into account in consequence of the method: the transmitter content, the directionality, and the occurrence of interposed synaptic contacts cannot be specified.

Olfactory discrimination and memory deficits in the Flinders Sensitive Line rodent model of depression

Major Depressive Disorder (MDD) is a heterogeneous psychiatric disorder with broad symptomatic manifestations. The current study examined, for the first time, olfactory memory and discrimination in the Flinders Sensitive Line (FSL) rodent model of depression. Male FSL rats and controls were trained on an Olfactory Discrimination (OD) and a Social Interaction (SI) test. On the OD test, the FSL and controls performed similarly at the shortest inter-trial interval (5min), however, with extended delay of 30min, the FSLs had a recall and odour discrimination deficit. At the longest delay (60min) both groups performed poorly. The FSL rats i.) had a deficit in olfactory discrimination suggesting impairment in olfactory memory and recall; ii.) were less likely to socialize with unfamiliar rats. The data suggests that FSL animals have an impaired olfactory information processing capacity.

Determining the Orientation of Directional Deep Brain Stimulation Electrodes Using 3D Rotational Fluoroscopy

BACKGROUND AND PURPOSE

New deep brain stimulation leads with electrode contacts that are split along their circumference allow steering of the electrical field in a predefined direction. However, imaging-assisted directional stimulation requires detailed knowledge of the exact orientation of the electrode array. The purpose of this study was to evaluate whether this information can be obtained by rotational 3D fluoroscopy.

MATERIALS AND METHODS

Two directional leads were inserted into a 3D-printed plaster skull filled with gelatin. The torsion of the lead tip versus the lead at the burr-hole level was investigated. Then, 3 blinded raters evaluated 12 3D fluoroscopies with random lead orientations. They determined the lead orientation considering the x-ray marker only and considering the overlap of the gaps between the contact segments. Intraclass correlation coefficients and an extended version of the Bland-Altman plot were used to determine interrater reliability and agreement of the measurements of the different raters.

RESULTS

Electrode torsion of up to 35° could be demonstrated. Evaluation of the lead rotation considering the x-ray marker only revealed limits of agreement of ±9.37° and an intraclass correlation coefficient of 0.9975. In addition, taking into account the lines resulting from overlapping of the gaps between the electrode segments, the limits of agreement to the mean were ±2.44° and an intraclass correlation coefficient of 0.9998.

CONCLUSIONS

In directional deep brain stimulation systems, rotational 3D fluoroscopy combined with the described evaluation method allows for determining the exact orientation of the leads, enabling the full potential of imaging-assisted personalized programming.

German registry of paediatric deep brain stimulation in patients with childhood-onset dystonia (GEPESTIM)

BACKGROUND

Data on paediatric deep brain stimulation (DBS) is limited, especially for long-term outcomes, because of small numbers in single center series and lack of systematic multi-center trials.

OBJECTIVES

We seek to systematically evaluate the clinical outcome of paediatric patients undergoing DBS.

METHODS

A German registry on paediatric DBS (GEPESTIM) was created to collect data of patients with dystonia undergoing DBS up to the age of 18 years. Patients were divided into three groups according to etiology (group 1 inherited, group 2 acquired, and group 3 idiopathic dystonia).

RESULTS

Data of 44 patients with a mean age of 12.8 years at time of operation provided by 6 German centers could be documented in the registry so far (group 1 n = 18, group 2 n = 16, group 3 n = 10). Average absolute improvement after implantation was 15.5 ± 18.0 for 27 patients with pre- and postoperative Burke-Fahn-Marsden Dystonia Rating scale movement scores available (p < 0.001) (group 1: 19.6 ± 19.7, n = 12; group 2: 7.0 ± 8.9, n = 8; group 3: 19.2 ± 20.7, n = 7). Infection was the main reason for hardware removal (n = 6). 20 IPG replacements due to battery expiry were necessary in 15 patients at 3.7 ± 1.8 years after last implantation.

DISCUSSION

Pre- and postoperative data on paediatric DBS are very heterogeneous and incomplete but corroborate the positive effects of DBS on inherited and acquired dystonia. Adverse events including relatively frequent IPG replacements due to battery expiry seem to be a prominent feature of children with dystonia undergoing DBS. The registry enables collaborative research on DBS treatment in the paediatric population and to create standardized management algorithms in the future.

Electrophysiologic Validation of Diffusion Tensor Imaging Tractography during Deep Brain Stimulation Surgery

BACKGROUND AND PURPOSE

Diffusion tensor imaging fiber tractography-assisted planning of deep brain stimulation is an emerging technology. We investigated its accuracy by using electrophysiology under clinical conditions. We hypothesized that a level of concordance between electrophysiology and DTI fiber tractography can be reached, comparable with published modeling approaches for deep brain stimulation surgery.

MATERIALS AND METHODS

Eleven patients underwent subthalamic nucleus deep brain stimulation. DTI scans and high-resolution T1- and T2-weighted MR imaging was performed at 3T. Corticospinal tracts were traced. We studied electrode positions and current amplitudes that elicited corticospinal tract effects during the operation to determine relative corticospinal tract distance. Postoperatively, 3D deep brain stimulation electrode contact locations and stimulation patterns were applied for the same corticospinal tract distance estimation.

RESULTS

Intraoperative electrophysiologic (n = 40) clinical effects in 11 patients were detected. The mean intraoperative electrophysiologic corticospinal tract distance was 3.0 ± 0.6 mm; the mean image-derived corticospinal tract distance (DTI fiber tractography) was 3.0 ± 1.3 mm. The 95% limits of agreement were ±2.4 mm. Postoperative electrophysiology (n = 44) corticospinal tract activation effects were encountered in 9 patients; 39 were further evaluated. Mean electrophysiologic corticospinal tract distance was 3.7 ± 0.7 mm; for DTI fiber tractography, it was 3.2 ± 1.9 mm. The 95% limits of agreement were ±2.5 mm.

CONCLUSIONS

DTI fiber tractography depicted the medial corticospinal tract border with proved concordance. Although the overall range of measurements was relatively small and variance was high, we believe that further use of DTI fiber tractography to assist deep brain stimulation procedures is advisable if inherent limitations are respected. These results confirm our previously published electric field simulation studies.

Ventral tegmental area dopaminergic lesion-induced depressive phenotype in the rat is reversed by deep brain stimulation of the medial forebrain bundle

DBS of the medial forebrain bundle (MFB) has been investigated clinically in major depressive disorder patients with rapid and long-term reduction of symptoms. In the context of chronic bilateral high frequency deep brain stimulation (DBS) of the MFB, the current study looked at the impact of lesioning the ascending dopaminergic pathway at the level of the ventral tegmental area (VTA). Sprague-Dawley female rats were given bilateral injection of 6-OHDA into the VTA (VTA-lx group) or were left unlesioned (control group). Later, all animals received bilateral microelectrode implantation into the MFB followed by chronic continuous stimulation for 3 weeks. Behavioral tests were performed as baseline and following MFB-DBS, along with histological analysis. Pre-stimulation baseline testing of the VTA-lx animals indicated depressive-like phenotype in comparison with controls. Response to MFB-DBS varied according to (i) the degree of dopaminergic depletion: animals with severe mesocorticolimbic dopamine depletion did not, whilst those with mild dopamine loss responded well to stimulation; (ii) environmental conditions and the nature of the behavioral tests, e.g., stressful vs non-stressful situations. Neuromodulation-induced c-fos expression in the prelimbic frontal cortex and nucleus accumbens was also dependent upon integrity of the dopaminergic ascending projections. Our results confirm a potential role for dopamine in symptom relief observed in clinical MFB-DBS. Although mechanisms are not fully understood, the data suggests that the rescue of depressive phenotype in rodents can work via both dopamine-dependent and independent mechanisms. Further investigations concerning the network of depression using neuromodulation platforms in animal models might give insight into genesis and treatment of major depression disorder.

Explaining clinical effects of deep brain stimulation through simplified target-specific modeling of the volume of activated tissue

BACKGROUND AND PURPOSE

Although progress has been made in understanding the optimal anatomic structures as target areas for DBS, little effort has been put into modeling and predicting electromagnetic field properties of activated DBS electrodes and understanding their interactions with the adjacent tissue. Currently, DBS is performed with the patient awake to assess the effectiveness and the side effect spectrum of stimulation. This study was designed to create a robust and rather simple numeric and visual tool that provides sufficient and practical relevant information to visualize the patient's individual VAT.

MATERIALS AND METHODS

Multivariate polynomial fitting of previously obtained data from a finite-element model, based on a similar DBS system, was used. The model estimates VAT as a first-approximation sphere around the active DBS contact, using stimulation voltages and individual tissue-electrode impedances. Validation uses data from 2 patients with PD by MR imaging, DTI, fiber tractography, and postoperative CT data.

RESULTS

Our model can predict VAT for impedances between 500 and 2000 Ω with stimulation voltages up to 10 V. It is based on assumptions for monopolar DBS. Evaluation of 2 DBS cases showed a convincing correspondence between predicted VAT and neurologic (side) effects (internal capsule activation).

CONCLUSIONS

Stimulation effects during DBS can be readily explained with this simple VAT model. Its implementation in daily clinical routine might help in understanding the types of tissues activated during DBS. This technique might have the potential to facilitate DBS implantations with the patient under general anesthesia while yielding acceptable clinical effectiveness.

[Long-term care of Parkinson patients with deep brain stimulation]

For more than 15 years deep brain stimulation of the subthalamic nucleus and globus pallidus internus have become therapeutic options in advanced Parkinson's disease. The number of patients with long-term treatment is increasing steadily. This review focuses on issues of the long-term care of these Parkinson's patients, including differences of the available deep brain stimulation systems, recommendations for follow-up examinations, implications for medical diagnostics and therapies and an algorithm for symptom deterioration. Today, there is no profound evidence that deep brain stimulation prevents disease progression. However, symptomatic relief from motor symptoms is maintained during long-term follow-up and interruption of the therapy remains an exception.

Minimizing brain shift during functional neurosurgical procedures - a simple burr hole technique that can decrease CSF loss and intracranial air

BACKGROUND

Exact stereotactic placement of deep brain stimulation electrodes during functional stereotactic neurosurgical procedures can be impeded by intraoperative brain shift. Brain shift has been shown to correlate with the amount of intracranial (subdural) air detected on early postoperative imaging studies. We report a simple burr hole technique that reduces the loss of cerebrospinal fluid (CSF) and has the potential to significantly reduce the amount of postoperative intracranial air.

MATERIAL AND METHODS

A total of 16 patients were studied with half (group 2) receiving the burr hole technique designed to seal the CSF space and thereby reducing CSF loss. The other 8 patients (group 1) received the standard burr hole technique. The 2 groups were of similar age, gender, diagnosis (Parkinson's disease, n=14; cervical dystonia n=2), and surgical targets. All patients received bilateral electrodes either in the subthalamic nucleus (STN, n=14) or in the globus pallidum internus (GPi, n=2) avoiding transventricular trajectories. Early postoperative 3-dimensional computed tomography (3D CT) was used to check for possible bleeding, DBS lead location, and the amount of intracranial air. Intracranial air was assessed manually in a volumetric slice-by-slice approach in the individual postoperative CT and the groups compared by t-test.

RESULTS

Group 2 showed significantly lower postoperative intracranial air volumes (4.86 ± 4.35cc) as compared to group 1 (27.59 ± 17.80 cc, p=0.0083*). The duration of surgery, however, was significantly longer for group 1 (435 ± 56.05 min) as compared to group 2 (316 ± 34.79 min,p=0.00015*).The time span between the conclusion of the operation and postoperative 3DCT was similar for both groups.

CONCLUSION

This new and simple burr hole technique was associated with a significant reduction in postoperative intracranial air. Reduction of intracranial air will ultimately reduce brain shift. That total operation time does not influence intracranial air is discussed as well as the limitations of this pilot series. In the authors' opinion, this straightforward and cost-effective technique has the potential to reduce brain shift and to increase DBS placement accuracy during functional stereotactic neurosurgical procedures performed in the seated or half-sitting position. A larger more standardized patient series is necessary to substantiate the findings.

[Deep brain stimulation for Parkinson's disease and camptocormia? A case report]

Camptocormia is recognised as a severe postural movement disorder complicating neurodegenerative diseases like Parkinson's disease (PD) and multisystem atrophy. Pathophysiologically two main hypotheses are discussed: (i) a disorder of the basal ganglia resulting in axial dystonia and rigidity on the one hand and (ii) an extensor truncal myopathy on the other hand. Therapeutic efforts often result in limited success. Therefore, reports on improvements by deep brain stimulation (DBS) are of great interest. However, the role of DBS in the treatment of camptocormia remains unclear. Here, we report a female PD patient who responded well to DBS of the subthalamic nucleus for severe dyskinesias and fluctuations. However, after 6 months she started to develop a rapidly progressing camptocormia which did not respond to DBS. The clinical and electrophysiological examination suggested a truncal erector myopathy. The inconsistent reports on the effects of DBS on camptocormia in PD patients suggest heterogeneous pathogenetic pathways. A pathophysiological subtype with predominant basal ganglia dysfunction and responsivity to DBS, however, seems to be rather rare. A myopathy, in contrast, seems to be more frequent and DBS is not effective in this condition. Therefore, camptocormia in PD patients is not an established indication for DBS.

Localization of the subthalamic nucleus: optimization with susceptibility-weighted phase MR imaging

BACKGROUND AND PURPOSE

On clinical MR images, the subthalamic nuclei (STN) are poorly delineated from adjacent structures, impeding safe direct targeting for placement of electrodes in the treatment of Parkinson disease. Susceptibility-weighted MR phase imaging offers improved contrast and spatial resolution at reduced imaging times relative to clinically used T2-weighted spin-echo imaging for STN visualization. Our purpose was to assess STN visibility by using phase imaging, comparing phase and magnitude images obtained concurrently by using susceptibility-weighted imaging (SWI). The goal was to identify an efficient scanning protocol for high-quality phase images of STN.

MATERIALS AND METHODS

Seventy-eight SWI scans were acquired at 3T by using different TEs and acceleration factors. STN visibility and delimitation from adjacent structures were scored from 0 (not interpretable) to 5 (excellent). Regression analyses assessed the relationship of STN visibility to scanning parameters

RESULTS

STN were identified at all studied TEs on phase images. Visibility and delimitation of STN were consistently superior on phase images compared with magnitude images. Good visualization (score of >or=4) of STN on phase imaging occurred at a mean TE of 20.0 ms and a sensitivity encoding (SENSE) of 1.40. Scores of STN visualization on phase images were dependent on SENSE (P < .002) and TE (P < .031). Good delimitation of the STN on phase imaging occurred at a mean TE of 21.6 ms and a SENSE of 1.36.

CONCLUSIONS

Visualization and delimitation of STN was superior on phase images and was achieved at 3T in <2.5 minutes. A TE of 20 ms and an acceleration factor of <or=1.5 are recommended to visualize STN by using this method.

Electrophysiological Proof of Diffusion-Weighted Imaging-Derived Depiction of the Deep-Seated Pyramidal Tract in Human

In the living human brain the pyramidal tract (PT) can be displayed with magnetic resonance diffusion-weighted imaging (DWI). Although this imaging technique is already being used for planning and performing neurosurgical procedures in the PT vicinity, there is a lack of verification of DWI accuracy in other areas outside the directly subcortical PT parts. Before definitive electrode placement into the subthalamic nucleus (STN) in patients with Parkinson disease (PD) for chronic stimulation, the stimulation effect on PD symptoms and the side-effects, namely PT activation at the level of the internal capsule (IC), are electrophysiologically tested. To analyze DWI accuracy by matching the stereotactic coordinates of the electrophysiologically proven IC position with these of the DWI-derived IC display, DWI was added to the routine MRI work-up in the stereotactic frame prior to functional surgery in 6 patients. In all of the 10 displayed fiber tracts, concordant findings for imaging and macrostimulation were made. The authors proved for the first time that DWI correctly depicts the deep seated, principle motor pathways in the living human brain. Due to methodical limitations of this study the accuracy of the proven IC display is limited to 3 mm which has proven to be sufficient for the planning and performance of neurosurgical procedures in the vicinity of large fiber tracts.

Subthalamic nucleus stimulation for advanced Parkinson's disease: how to find a far medial STN

In a patient with advanced Parkinson's disease, an anatomically deviant far medial subthalamic nucleus (STN) posed problems in the placement of DBS electrodes for chronic high frequency (HF) stimulation despite the use of multimodal targeting with 1) statistical atlas data, 2) T (2)-weighted (T (2)W) magnetic resonance imaging (MRI), 3) microelectrode recording, and 4) clinical testing with macro stimulation. Diagnostic T (2)W MRI suggested that the patient's STN was in a typical location and seemed to confirm the statistical atlas-based planning. Intraoperatively, cell activity recording (MER) with five parallel electrodes could not reveal any STN typical activity profile and electrical stimulation was not able to disclose a medial or lateral displacement of the electrodes. The operation was discontinued and postoperative stereotactic CT confirmed that the correct target area had been approached during the operation. Postoperative T (2)W MRI now disclosed a left STN which was 2 mm medial of the initial target and lead to a further medial target definition and finally to a successful DBS placement. In conclusion, finding a deep seated DBS target like the STN can be difficult in cases with an extremely deviant anatomy even if reiterative sophisticated multimodal planning is used. In the presented case we applied the integrated information from intraoperative MER, macrostimulation and postoperative imaging work-up and were able to complete DBS implantation successfully.

Diffusion-weighted imaging-guided resection of intracerebral lesions involving the optic radiation

In this paper we report our experience with diffusion-weighted imaging (DWI) for optic radiation (OR) visualization during resection of tumors. We hypothesize that intraoperative OR visualization helps to maintain patients' visual fields. DWI studies were performed together with T1-weighted postcontrast magnetic resonance imaging (MRI) in four patients with lesions in or adjacent to the OR (glioblastoma, oligo-astrocytoma, cavernoma, and metastasis; n = 1 each). The OR was identified from one of six DWI data acquisitions, segmented and reconstructed three-dimensionally. The image data were neuronavigationally transferred into the operative field, and provided the neurosurgeon with information on lesion site and adjacent OR localization. Preoperative and postoperative neuroophthalmological testing included, among others, perimetry to define the value of diffusion-weighted image guidance during OR lesion resection. Three lesions were removed completely. In one case, low-grade tumor parts infiltrating the OR were intentionally left. No persistent visual field deficits were induced. In one patient, a transient homonymous hemianopia attributable to postoperative swelling completely resolved under steroid medication. The authors conclude that intraoperative OR visualization, realized by neuronavigationally displayed DWI data, might prove to be helpful to maintain patients' visual fields.

Advanced Neuronavigation in Skull Base Tumors and Vascular Lesions

OBJECTIVE

The purpose of this study was to describe the usefulness of recent advances of neuronavigational technology in the management of skull base tumors and of vascular lesions, treated via a skull base approach.

METHODS

In 16 patients (skull base meningioma n = 9, petrous apex epidermoid n = l, craniopharyngeoma n = 1, giant internal carotid artery aneurysm n = 1, basilar/vertebral artery aneurysm n = 2, brain stem cavernoma n = 2), "advanced" neuronavigation was used. In contrast to "conventional" neuronavigation, the information for the neurosurgeon was enhanced by the intraoperative screen display of 3-dimensional reconstructions of the lesion, vessels, nerves and fiber tracts at risk. The 3-dimensional reconstructions were obtained by preoperative manual or automated segmentation processes. In addition, different imaging modalities (computed tomography [CT] with magnetic resonance imaging [MRI], CT with CT angiography, T (l)- with diffusion-weighted MRI) were fused and shown on the screen.

RESULTS

In the cases of tumors, "advanced" neuronavigation facilitated the approach (n = 4), contributed to tailor the approach (n = 2) and helped to identify hidden neurovascular structures (n = 9). In the cases of aneurysms, "advanced" neuronavigation allowed us to reduce the skull base approach to the needs of safe aneurysm clipping (n = 3). In both cases of brain stem cavernoma, "advanced" neuronavigation was deemed useful for definition of the best surgical approach in relation to the pyramidal tract and brain stem nuclei.

CONCLUSION

The authors' experiences suggest that neuronavigation, which displays 3-dimensional reconstructions of lesion, vessels, nerves and fiber tracts during surgery and makes use of image fusion techniques, is an important tool in the neurosurgical management of skull base lesions.

Image-guided microneurosurgical management of small cerebral arteriovenous malformations: the value of navigated computed tomographic angiography

In small arteriovenous malformations (AVM) with large hematomas, surgery remains the main therapeutic option. However, intraoperative identification of the AVM, feeders, and draining veins could be difficult in the environment of substantial intracerebral blood. In those selected cases, we use navigated computed tomographic angiography (CTA) for the microneurosurgical management. It is our objective to report our initial experiences. Prior to operation a conventional CTA with superficial skin fiducials placed on a patient's head was acquired for diagnostic and neuronavigation purposes. Image data were transferred to a neuronavigation device with integrated volume rendering capacities which allows a three-dimensional reconstruction of the vascular tree and the AVM to be created. In all patients the AVM was removed successfully after having been localized with CTA-based neuronavigation. Navigated CTA is helpful for the operative management of small AVMs with large hematomas. The technique allows feeding arteries to be distinguished from draining veins thereby allowing the nidus of the AVM to be identified despite the presence of substantial intracerebral blood. CTA can be easily implemented into commercial neuronavigation systems.

[Diffusion Weighted Imaging Combined with Intraoperative 3D-Ultrasound and fMRI for the Resection of an Optic Radiation Cavernoma]

A 17-year-old patient with a symptomatic cavernoma of the optic radiation underwent surgery supported by functional magnetic resonance imaging (fMRI), diffusion weighted magnetic resonance imaging (DWI) and navigated 3D-ultrasound. The primary visual cortex was visualized with fMRI. The optic radiation was delineated by means of DWI. The diffusion weigthed images were used for 3-dimensional reconstruction of the optic radiation. During surgery, the information of the localisation of functional brain regions were used together with the 3D-ultrasound, enabling the surgeon to remove the cavernoma without morbidity. This is the first report of the combined use of fMRI, fiber tract imaging and 3D-ultrasound for the safe resection of an optic radiation lesion.

In vivo 3D visualization of normal pyramidal tracts in human subjects using diffusion weighted magnetic resonance imaging and a neuronavigation system

We describe the potential of anisotropic diffusion weighted imaging to visualize the course of large cerebral fiber tracts. Five healthy volunteers were investigated at a field strength of 1.5 Tesla, employing a spin-echo diffusion weighted sequence with gradient sensitivity in six non-collinear directions to visualize the course of the pyramidal tracts. The pyramidal tracts were segmented and reconstructed for three-dimensional visualization. Reconstruction results together with a fusioned high resolution 3D T1 weighted image data set were available in a customized neuronavigation system. Origination in the primary motor cortex, convergence in the centrum semiovale, the posterior limb of the internal capsule, the cerebral peduncles, the splitting at the level of the pons, and the pyramidal decussation were identified in all subjects. Fiber tract maps might have the prospect of guiding neurosurgical interventions, especially when being linked to a neuronavigation system. Other potential applications include the demonstration of the anatomical substrate of functional connectivity in the human brain.

Three-dimensional visualization of the pyramidal tract in a neuronavigation system during brain tumor surgery: first experiences and technical note

OBJECTIVE

To integrate spatial three-dimensional information concerning the pyramidal tracts into a customized system for frameless neuronavigation during brain tumor surgery.

METHODS

Four consecutive patients with intracranial tumors in eloquent areas underwent diffusion-weighted and anatomic magnetic resonance imaging studies within 48 hours before surgery. Diffusion-weighted datasets were merged with anatomic data for navigation purposes. The pyramidal tracts were segmented and reconstructed for three-dimensional visualization. The reconstruction results, together with the fused-image dataset, were available during surgery in the environment of a customized neuronavigation system.

RESULTS

In all four patients, the combination of reconstructed data and fused images was a helpful additional source of information concerning the tumor seat and topographical interaction with the pyramidal tract. In two patients, intraoperative motor cortex stimulation verified the tumor seat with regard to the precentral gyrus.

CONCLUSION

Diffusion-weighted magnetic resonance imaging allows individual estimation of large fiber tracts applicable as important information in intraoperative neuronavigation and in planning brain tumor resection. A three-dimensional representation of fibers associated with the pyramidal tract during brain tumor surgery is feasible with the presented technique and is a helpful adjunct for the neurosurgeon. The main drawbacks include the length of time required for the segmentation procedure, the lack of direct intraoperative control of the pyramidal tract position, and brain shift. However, mapping of large fiber tracts and its intraoperative use for neuronavigation have the potential to increase the safety of neurosurgical procedures and to reduce surgical morbidity.

Evidence of a smaller left hippocampus and left temporal horn in both patients with first episode schizophrenia and normal control subjects

Findings from cerebral magnetic resonance imaging (MRI) studies in schizophrenia indicating temporal lobe involvement have been inconsistent and controversial. In a prospective study, we quantified the volumes of temporal lobe structures in 20 male patients with first episode schizophrenia (FES; mean+/-S.D.=27.4+/-4. 8 years) and 20 healthy age-matched male control subjects (27.7+/-3. 1 years). Measurements were performed on contiguous 2.2-mm coronal MRI slices, which included, as well as the temporal lobe, the amygdala, the hippocampal formation, and the temporal horn of the lateral ventricle. The definition of the borders of the structures relied on measurement guidelines derived from mutual comparisons of MRI and histological data. The definition of the hippocampus-amygdala interface was also validated in a correlated triplanar display. We did not detect any significant volume reductions of the measured structures in the FES group, as compared with healthy control subjects, on either side. Comparisons within groups, however, revealed that in both the patients and the healthy volunteers the hippocampal formations showed a significant right-sided bias (+9%, P=0.004, in the FES group; +12%, P=0.0003 in the control subjects). A significant volume difference in favor of the right hemisphere was also observed in the temporal horns of the lateral ventricles (+17%, P=0.02 in the patients with FES; +34%, P=0. 003, in the control group). There was only a nonsignificant trend for a larger temporal horn on the left side in patients with schizophrenia as compared with the control subjects. Our findings do not indicate a loss or reversal of the normal volume asymmetry pattern in the FES group.

Efficacy of transluminal angioplasty for the management of symptomatic cerebral vasospasm following aneurysmal subarachnoid hemorrhage

OBJECT

Transluminal angioplasty has become a widely used adjunct therapy to medical management of symptomatic cerebral vasospasm following subarachnoid hemorrhage (SAH). Despite anecdotal reports of universal, angiographically confirmed reversal of vasospasm and high rates of clinical improvement, no rigorous examination of the efficacy of this procedure has been conducted. In this study the authors assess the efficacy of the aforementioned procedure.

METHODS

Thirty-eight patients enrolled as part of the North American trial of tirilazad in aneurysmal SAH underwent transluminal angioplasty for symptomatic cerebral vasospasm. Fifty-three percent of these patients showed good recovery or moderate disability based on their 3-month Glasgow Outcome Scale score. Among the 38 patients who underwent angioplasty, the severity and type of vasospasm, use of papaverine in addition to balloon angioplasty, timing of treatment, and dose of study drug did not have an effect on the outcome. The results of their neurological examinations improved in only four of the 38 patients immediately after the procedure. A conditional logistic regression analysis was performed in which these patients were compared with individuals matched for age, sex, dose of study drug, admission neurological grade, and modified Glasgow Coma Scale score at the time of angioplasty. No effect on favorable outcomes was found for this procedure.

CONCLUSIONS

Transluminal cerebral angioplasty is very effective in reversing angiographically confirmed vasospasm, and anecdotal reports of its clinical utility are numerous. However, in this report the authors conclude that its superiority to medical management for symptomatic cerebral vasospasm is questionable.

Endovascular treatment for symptomatic cerebral vasospasm after subarachnoid hemorrhage: transluminal balloon angioplasty compared with intraarterial papaverine

The authors retrospectively evaluated the short-term neurological improvement of 69 patients undergoing endovascular treatment for symptomatic cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The patient group observed here is a subset of patients enrolled in the multicenter North American Trial of Tirilazad in SAH. Thirty-one patients were treated with intraarterial administration of papaverine (IAP). Fourteen patients were only treated with transluminal balloon angioplasty (TBA), and 24 patients received a combination of angioplasty and papaverine.

The purpose of this study was to compare the effects of IAP and TBA on short-term clinical improvement of patients. Daily clinical staging with the modified Glasgow Coma Scale and every-other-day transcranial Doppler (TCD) measurements allowed for a close investigation of the clinical course. Furthermore, this study was designed to investigate the effects of treatment timing on short-term outcome.

Although TCD studies demonstrated a decrease in flow velocities in the middle cerebral artery in both treatment groups, indicating a vasodilating effect of both treatment modalities (dv = -18.4 cm/second for papaverine, dv = -26.04 cm/second for angioplasty; p = 0.5509), there was no significant difference in clinical improvement at Days 1 and 4 postprocedure (p = 0.1996). Neither of the two treatment forms showed an effect of therapy timing on neurological outcome.

Neither IAP nor TBA was correlated with a high percentage of short-term neurological improvement. The authors discuss reasons why those procedures may result in limited clinical change.