Presurgical motor and somatosensory cortex mapping with functional magnetic resonance imaging and positron emission tomography

Rolandic Cortex Morphology: Magnetic Resonance Imaging-Based Three-Dimensional Cerebral Reconstruction Study and Intraoperative Usefulness

Background  During brain surgery, the neurosurgeon must be able to identify and avoid injury to the Rolandic cortex. However, when only a small part of the cortex is exposed, it may be difficult to identify the Rolandic cortex with certainty. Despite various advanced methods to identify it, visual recognition remains an important backup for neurosurgeons. The aim of the study was to find any specific morphology pattern that may help to identify the Rolandic cortex intraoperatively.

Materials and Methods  Magnetic resonance imaging of the brain from patients with various conditions was used to create the three-dimensional cerebral reconstruction images. A total of 216 patients with 371 intact hemispheres were included. Each image was inspected to note the morphology of the Rolandic cortex and the suprasylvian cortex. Additionally, other two evaluators exclusively inspected the morphology of the suprasylvian cortex. Their observation results were compared to find the agreements.

Results  Several distinctive morphology patterns have been identified at the Rolandic cortex and the suprasylvian cortex including a genu, or a knob at the upper precentral gyrus, an angulation of the lower postcentral gyrus, a strip for pars opercularis, a rectangle for the lower precentral gyrus, and a triangle for the lower postcentral gyrus. Combined total and partial agreement of the suprasylvian cortex morphology pattern ranged from 60.4 to 85.2%.

Conclusion  The authors have demonstrated the distinctive morphology of the Rolandic cortex and the suprasylvian cortex. This information can provide visual guidance to identify the Rolandic cortex particularly during surgery with limited exposure.

Outcomes of tumour related epilepsy in a specialised epilepsy surgery unit

INTRODUCTION

Seizures are an important cause of morbidity in patients with low grade gliomas with approximately 40% of cases drug resistant. The pathogenesis is quite complex and poorly understood. The treatment aims vary between almost purely epilepsy considerations and those that are primarily oncologic.

AIM

To determine whether patients who present with seizures and are found to have a low grade glioma have better outcomes when managed through a specialized epilepsy unit compared to the general neurosurgical service.

METHODS

A review of the prospectively collected database was performed over a 10 year period to identify 48 adult patients who present with a seizure and were subsequently found to have a low grade glioma. These patients were analysed with respect to management through the specialized epilepsy service or the general neurosurgical service. The primary outcome was Engel classification between the two groups. Secondary outcomes included recurrence, postoperative deficits, delay to surgery, histology, grade and extent of resection.

OUTCOMES

The patients managed through the epilepsy service had significantly higher rate of favourable Engel outcomes (I and II) compared to the general neurosurgery service (OR: 13.2, 95% CI: 1.239-140.679; P = 0.033). The epilepsy surgery group patients had a significantly higher delay to surgery (P < 0.001). The patients in the epilepsy service had a significantly higher resection ratio compared to the general neurosurgery service (73% vs 127%, P = 0.014). Rates of recurrence were not different between the two groups.

CONCLUSION

Patients with tumour related epilepsy who undergo an intensive presurgical evaluation may obtain better seizure related outcomes.

Electrocorticographic Temporal Alteration Mapping: A Clinical Technique for Mapping the Motor Cortex with Movement-Related Cortical Potentials

We propose electrocorticographic temporal alteration mapping (ETAM) for motor cortex mapping by utilizing movement-related cortical potentials (MRCPs) within the low-frequency band [0.05-3] Hz. This MRCP waveform-based temporal domain approach was compared with the state-of-the-art electrocorticographic frequency alteration mapping (EFAM), which is based on frequency spectrum dynamics. Five patients (two epilepsy cases and three tumor cases) were enrolled in the study. Each patient underwent intraoperative direct electrocortical stimulation (DECS) procedure for motor cortex localization. Moreover, the patients were required to perform simple brisk wrist extension task during awake craniotomy surgery. Cross-validation results showed that the proposed ETAM method had high sensitivity (81.8%) and specificity (94.3%) in identifying sites which exhibited positive DECS motor responses. Moreover, although the sensitivity of the ETAM and EFAM approaches was not significantly different, ETAM had greater specificity compared with EFAM (94.3 vs. 86.1%). These results indicate that for the intraoperative functional brain mapping, ETAM is a promising novel approach for motor cortex localization with the potential to reduce the need for cortical electrical stimulation.

Functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) maps the spatiotemporal distribution of neural activity in the brain under varying cognitive conditions. Since its inception in 1991, blood oxygen level-dependent (BOLD) fMRI has rapidly become a vital methodology in basic and applied neuroscience research. In the clinical realm, it has become an established tool for presurgical functional brain mapping. This chapter has three principal aims. First, we review key physiologic, biophysical, and methodologic principles that underlie BOLD fMRI, regardless of its particular area of application. These principles inform a nuanced interpretation of the BOLD fMRI signal, along with its neurophysiologic significance and pitfalls. Second, we illustrate the clinical application of task-based fMRI to presurgical motor, language, and memory mapping in patients with lesions near eloquent brain areas. Integration of BOLD fMRI and diffusion tensor white-matter tractography provides a road map for presurgical planning and intraoperative navigation that helps to maximize the extent of lesion resection while minimizing the risk of postoperative neurologic deficits. Finally, we highlight several basic principles of resting-state fMRI and its emerging translational clinical applications. Resting-state fMRI represents an important paradigm shift, focusing attention on functional connectivity within intrinsic cognitive networks.

Microsurgical anatomy of the central lobe

OBJECT

Central Lobe consists of the pre- and postcentral gyri on the lateral surface and the Paracentral Lobule on the medial surface and corresponds to the sensorimotor cortex. The objective of the present study was to define the neural features, craniometric relationships, arterial supply, and venous drainage of the central lobe.

METHODS

Cadaveric hemispheres dissected using microsurgical techniques provided the material for this study.

RESULTS

The coronal suture is closer to the precentral gyrus and central sulcus at its lower rather than at its upper end, but they are closest at a point near where the superior temporal line crosses the coronal suture. The arterial supply of the lower two-thirds of the lateral surface of the central lobe was from the central, precentral, and anterior parietal branches that arose predominantly from the superior trunk of the middle cerebral artery. The medial surface and the superior third of the lateral surface were supplied by the posterior interior frontal, paracentral, and superior parietal branches of the pericallosal and callosomarginal arteries. The venous drainage of the superior two-thirds of the lateral surface and the central lobe on the medial surface was predominantly through the superior sagittal sinus, and the inferior third of the lateral surface was predominantly through the superficial sylvian veins to the sphenoparietal sinus or the vein of Labbé to the transverse sinus.

CONCLUSIONS

The pre- and postcentral gyri and paracentral lobule have a morphological and functional anatomy that differentiates them from the remainder of their respective lobes and are considered by many as a single lobe. An understanding of the anatomical relationships of the central lobe can be useful in preoperative planning and in establishing reliable intraoperative landmarks.

Blood oxygen level dependent functional magnetic resonance imaging for presurgical planning

Functional magnetic resonance imaging (fMRI) has become a common tool for presurgical sensorimotor mapping, and is a significant preoperative asset for tumors located adjacent to the central sulcus. fMRI has changed surgical options for many patients. This noninvasive tool allows for easy display and integration with other neuroimaging techniques. Although fMRI is a useful preoperative tool, it is not perfect. Tumors that affect the normal vascular coupling of neuronal activity will affect fMRI measurements. This article discusses the usefulness of blood oxygen level dependent (BOLD) fMRI with regard to preoperative motor mapping.

A comprehensive neuropsychological mapping battery for functional magnetic resonance imaging

Existing batteries for FMRI do not precisely meet the criteria for comprehensive mapping of cognitive functions within minimum data acquisition times using standard scanners and head coils. The goal was to develop a battery of neuropsychological paradigms for FMRI that can also be used in other brain imaging techniques and behavioural research. Participants were 61 healthy, young adult volunteers (48 females and 13 males, mean age: 22.25 ± 3.39 years) from the university community. The battery included 8 paradigms for basic (visual, auditory, sensory-motor, emotional arousal) and complex (language, working memory, inhibition/interference control, learning) cognitive functions. Imaging was performed using standard functional imaging capabilities (1.5-T MR scanner, standard head coil). Structural and functional data series were analysed using Brain Voyager QX2.9 and Statistical Parametric Mapping-8. For basic processes, activation centres for individuals were within a distance of 3-11 mm of the group centres of the target regions and for complex cognitive processes, between 7 mm and 15 mm. Based on fixed-effect and random-effects analyses, the distance between the activation centres was 0-4 mm. There was spatial variability between individual cases; however, as shown by the distances between the centres found with fixed-effect and random-effects analyses, the coordinates for individual cases can be used to represent those of the group. The findings show that the neuropsychological brain mapping battery described here can be used in basic science studies that investigate the relationship of the brain to the mind and also as functional localiser in clinical studies for diagnosis, follow-up and pre-surgical mapping.

Fast presurgical functional mapping using task-related intracranial high gamma activity

OBJECT

Electrocorticography (ECoG) is a powerful tool for presurgical functional mapping. Power increase in the high gamma band has been observed from ECoG electrodes on the surface of the sensory motor cortex during the execution of body movements. In this study the authors aim to validate the clinical usage of high gamma activity in presurgical mapping by comparing ECoG mapping with traditional direct electrical cortical stimulation (ECS) and functional MRI (fMRI) mapping.

METHODS

Seventeen patients with epilepsy participated in an ECoG motor mapping experiment. The patients executed a 5-minute hand/tongue movement task while the ECoG signal was recorded. All 17 patients also underwent extraoperative ECS mapping to localize the motor cortex. Eight patients also participated in a presurgical fMRI study. The high gamma activity on ECoG was modeled using the general linear model (GLM), and the regions showing significant gamma power increase during the task condition compared with the rest condition were localized. The maps derived from GLM-based ECoG mapping, ECS, and fMRI were then compared.

RESULTS

High gamma activity in the motor cortex can be reliably modulated by motor tasks. Localization of the motor regions achieved with GLM-based ECoG mapping was consistent with the localization determined by ECS. The maps also appeared to be highly localized compared with the fMRI activations. Using the ECS findings as the reference, GLM-based ECoG mapping showed a significantly higher sensitivity than fMRI (66.7% for ECoG, 52.6% for fMRI, p<0.05), while the specificity was high for both techniques (>97%). If the current-spreading effect in ECS is accounted for, ECoG mapping may produce maps almost identical to those produced by ECS mapping (100% sensitivity and 99.5% specificity).

CONCLUSIONS

General linear model-based ECoG mapping showed a superior performance compared to traditional ECS and fMRI mapping in terms of efficiency and accuracy. Using this method, motor functions can be reliably mapped in less than 5 minutes.

Factors Affecting Successful Localization of the Central Sulcus Using the Somatosensory Evoked Potential Phase Reversal Technique

BACKGROUND:

Perirolandic surgery is associated with an increased risk of postoperative neurological deficit that can be reduced by accurate recognition of the location of sensorimotor cortex. The median somatosensory evoked potential (MSSEP) phase reversal technique (PRT) reliably identifies the central sulcus (CS) intraoperatively, but does require additional surgical time. Awareness of factors that lengthen the time required for MSSEP PRT has important implications for surgical planning.

OBJECTIVE:

To identify factors that affect the time required for CS localization via MSSEP PRT.

METHODS:

Multivariate Cox regression analysis, applied in 100 consecutive cases of perirolandic surgery at a single institution from 2005 to 2010, during which CS localization was attempted via a standardized MSSEP PRT.

RESULTS:

The CS was reliably identified in 77 cases. The mean time to identification was 5 minutes (SD = 5; range, 1–20 minutes). Lesion location either very close to the CS (within the postcentral gyrus) or at an intermediate distance (with edema extending very close to the CS) independently decreased the rate at which the CS was identified by 73% (hazard ratio: 0.27, P &lt; .001) and 55% (hazard ratio: 0.45, P = .007), respectively. Highly destructive pathology reduced this rate by 42% (hazard ratio: 0.58, P = .03), after adjusting for other important factors. Epidural recording, age, and the presence of a burst suppression pattern on the electroencephalogram had no effect.

CONCLUSION:

MSSEP PRT is an effective method for CS identification and only marginally lengthens the operative time. However, difficulty in CS localization can be expected in the presence of postcentral gyrus lesions, edema distorting perirolandic anatomy, and with highly destructive pathology.

Multimodal imaging and image analysis techniques for neuromodulation

Functional neurosurgical procedures used to treat the debilitating motor symptoms of Parkinson's disease and that target small subcortical structures have typically relied on semi-qualitative manual approaches that rely upon the establishing qualitative between volumetric imaging data and print atlases. This chapter reviews many new high -precision and -accuracy techniques that can be used for the full automated localization of these targets. These techniques rely on the a priori development of neuroanatomical atlases derived from magnetic resonance imaging data, high-resolution identification of subcortical structures from histology, and spatially localized data bases of intra-operative recordings and successful surgical outcomes. Other novel structural and functional MRI techniques that allow for the direct visualization of thalamic sub nuclei are also reviewed.

Clinical magnetoencephalography for neurosurgery

Noninvasive neuroimaging aids in surgical planning and in counseling patients about possible risks of surgery. Magnetoencephalography (MEG) performs the most common types of surgical planning that the neurosurgeon faces, including localization of epileptic discharges, determination of the hemispheric dominance of verbal processing, and the ability to locate eloquent cortex. MEG is most useful when it is combined with structural imaging, most commonly with structural magnetic resonance (MR) imaging and MR diffusion imaging. This article reviews the history of clinical MEG, introduces the basic concepts about the biophysics of MEG, and outlines the basic neurosurgical applications of MEG.

Localisation of the central sulcus region in glioma patients with three-dimensional fluid-attenuated inversion recovery and volume rendering: comparison with functional and conventional magnetic resonance

PURPOSE

Volume rendering (VR) of three-dimensional (3D) fluid-attenuated inversion recovery (FLAIR) magnetic resonance (MR) images shows regional intensity differences, reflecting the central sulcus (CS) region and occipital cortex. The purpose of this study was to determine whether 3D FLAIR with VR could be used as an alternative method to localise the CS region in comparison with functional and conventional MR-imaging in patients with perirolandic glioma.

METHODS

Eleven patients with intracranial gliomas were studied with single-slab 3D FLAIR including VR and conventional T1-weighted imaging. In all patients, preoperative functional magnetic resonance imaging (fMRI) was performed with a motor paradigm of the hand. The hypo-intense central gyri on 3D FLAIR with VR were interpreted as the CS area. Localisation of the motor hand knob on anatomical images and fMRI results were used for identification of the primary motor cortex.

RESULTS

Anatomical localisation of the motor hand knob on T1-weighted images was possible in 91% of both hemispheres. In 73% of the affected hemispheres (AH) and 91% of the unaffected hemispheres (UH) the hand knob and CS region could be identified on 3D FLAIR axial and VR images, respectively. With one exception, fMRI activation confirmed the CS region as observed with 3D FLAIR with VR.

CONCLUSIONS

Volume rendering of 3D FLAIR MR images shows central hypo-intensities frequently corresponding with the CS region. Two-dimensional localisation of the CS region on conventional T1-weighted images and fMRI seems favourable compared to 3D FLAIR. However, in selected cases, especially where fMRI is not possible or feasible, volume rendering with 3D FLAIR may enhance the 3D visualisation of gliomas in relation to the CS region which can be used as an alternative method in the presurgical structural and functional evaluation of neurosurgical patients.

Imaging in the surgical treatment of epilepsy

Medically refractory focal epilepsy is potentially curable by surgery. This Review considers the application of recent advances in structural and functional brain imaging to increase the number of patients with epilepsy who are treated surgically, and to reduce the risk of complications arising from such intervention. Current optimal MRI of brain structure can identify previously undetectable lesions, with voxel-based and quantitative analyses further increasing the diagnostic yield. If MRI proves unremarkable, PET (with (18)F-fluorodeoxyglucose) and single-photon emission CT of ictal-interictal cerebral blood flow might identify the brain region that contains the epileptic focus. Magnetoencephalography plus simultaneous EEG and functional MRI can map the location of interictal epileptic discharges, thereby facilitating placement of intracranial recording electrodes to define the site of seizure onset. Functional MRI can also lateralize language and localize primary motor, somatosensory and language areas, and shows promise for predicting the effects of temporal lobe resection on memory. Tractography can visualize the main cerebral white matter tracts, thereby predicting and reducing surgery risk. Currently, displays of the optic radiation and pyramidal tracts are the most relevant for epilepsy surgery. Reliable integration of structural and functional data into surgical image-guidance systems is being pursued, and promises safer neurosurgery for epilepsy in the future.

Passive real-time identification of speech and motor cortex during an awake craniotomy

Precise localization of eloquent cortex is a clinical necessity prior to surgical resections adjacent to speech or motor cortex. In the intraoperative setting, this traditionally requires inducing temporary lesions by direct electrocortical stimulation (DECS). In an attempt to increase efficiency and potentially reduce the amount of necessary stimulation, we used a passive mapping procedure in the setting of an awake craniotomy for tumor in two patients resection. We recorded electrocorticographic (ECoG) signals from exposed cortex while patients performed simple cue-directed motor and speech tasks. SIGFRIED, a procedure for real-time event detection, was used to identify areas of cortical activation by detecting task-related modulations in the ECoG high gamma band. SIGFRIED's real-time output quickly localized motor and speech areas of cortex similar to those identified by DECS. In conclusion, real-time passive identification of cortical function using SIGFRIED may serve as a useful adjunct to cortical stimulation mapping in the intraoperative setting.

Task-free presurgical mapping using functional magnetic resonance imaging intrinsic activity

OBJECT

Low-frequency components of the spontaneous functional MR imaging signal provide information about the intrinsic functional and anatomical organization of the brain. The ability to use such methods in individual patients may provide a powerful tool for presurgical planning. The authors explore the feasibility of presurgical motor function mapping in which a task-free paradigm is used.

METHODS

Six surgical candidates with tumors or epileptic foci near the motor cortex participated in this study. The investigators directly compared task-elicited activation of the motor system to activation obtained from intrinsic activity correlations. The motor network within the unhealthy hemisphere was identified based on intrinsic activity correlations, allowing distortions of functional anatomy caused by the tumor and epilepsy to be directly visualized. The precision of the motor function mapping was further explored in 1 participant by using direct cortical stimulation.

RESULTS

The motor regions localized based on the spontaneous activity correlations were quite similar to the regions defined by actual movement tasks and cortical stimulation. Using intrinsic activity correlations, it was possible to map the motor cortex in presurgical patients.

CONCLUSIONS

This task-free paradigm may provide a powerful approach to map functional anatomy in patients without task compliance and allow multiple brain systems to be determined in a single scanning session.

Design, construction, and validation of an MRI-compatible vibrotactile stimulator intended for clinical use

Vibrotactile stimulation has been used successfully to activate the human somatosensory pathway in functional magnetic resonance imaging (fMRI) experiments. The design and characterization of these devices are of particular interest in frequency discrimination tasks and investigations of the somatopic organization of sensory areas. However, few have investigated the utility of vibrotactile stimulation in a clinical context. We have previously demonstrated that vibrotactile stimulation can provide robust activations in areas targeted in stereotactic functional neurosurgical procedures used for tumour resection (i.e.: primary and secondary somatosensory areas) and subcortical targets for thalamic pain and movement disorders (i.e.: sensory thalamus). The main contribution of this manuscript is the presentation of the design, materials, construction, and validation of a novel vibrotactile stimulator intended for clinical use. The thalamic activations are also compared to a digital atlas in order to evaluate anatomical localization. The proposed stimulator was constructed entirely from non-ferromagnetic parts, uses compressed air to deliver stimulation using computer control, and stimulates the entirety of the hand and fingers to ensure robust somatosensory activations. In addition, this stimulator is constructed entirely from "off-the-shelf" parts and would be easily replicated due to the simplicity of design and the relatively small expense of the parts required. The device was tested by stimulating the right hand of 10 normal controls (5 females, 5 males, all right handed; age range: 25-42 years, mean: 30.9 years, standard deviation: 5.2 years) during an fMRI experiment. The results demonstrate significant single subject activations of primary and secondary somatosensory cortices and of the sensory thalamus.

Robust S1, S2, and thalamic activations in individual subjects with vibrotactile stimulation at 1.5 and 3.0 T

Functional magnetic resonance imaging (fMRI) is often used to enhance visualization and provide target localization during the planning phase of neurosurgical procedures. Although parametric maps have been used to identify areas of eloquent cortex such as the primary (S1) and secondary (S2) somatosensory areas for tumor surgery, to date, few fMRI methods exist to localize subcortical targets for surgical interventions used to treat movement disorders. The scanning time required to obtain statistically significant functional signals must be balanced against the possibility of movement artifacts and patient discomfort. We propose a vibrotactile stimulation technique to activate the somatosensory pathway for neurosurgical planning and perform a sensitivity analysis to determine the amount of time required to achieve significant activations of S1, S2, and sensory thalamus in individual subjects. Bilateral stimulation experiments were carried out on two MRI scanners (n = 13 at 1.5 T; n = 5 at 3.0 T). The analysis demonstrates that statistically significant functional activations can be achieved in clinically acceptable times: 16 min at 1.5 T (26/26 experiments) and 6 min at 3.0 T (10/10) for S1 activations; 24 min at 1.5 T (22/26) and 18 min at 3.0 T for S2 activations (9/10); and 32 min at 1.5 T (15/26) and 18 min at 3.0 T (10/10) for activation of thalamic nuclei. These results demonstrate that S1 and S2 activations are robust at 1.5 and 3.0 T, and that robust thalamic activations in individual subjects are possible at 3.0 T. These techniques demonstrate that this technique can be used for preoperative planning for surgical candidates.

Relationship between the coronal suture and the central lobe: how important is it and how can we use it in surgical planning?

The surgical treatment of the lesions located in the central lobe is a very difficult task for the neurosurgeon. The overall aim of this study is to verify the correlation of the coronal suture and the structures of the central lobe in 32 cadaver hemisphere brains and the importance of this information in surgical planning. The measurement of the nasion to the coronal suture ranged from 11.5 to 13.5 cm. The distance between the coronal suture in the midline to the central, precentral and paracentral sulcus ranged from 5.0 to 6.6, 2.5 to 4.5 and 1.3 to 4.0 cm respectively. Particularly in the normal cortex these measurements can be used to guide the surgical access. However, the identification of the central sulcus is not easy when the anatomical pattern is distorted or displaced by a lesion or edema. In cases such as these the use of other tools becomes crucial for good surgical planning and cortical mapping or awake craniotomy for a safer resection of the lesion as well.

The topographic anatomy of the central artery: a neuronavigational-based study

BACKGROUND/AIM

The central area of the brain, including the pre- and post-central gyri with their vascular structures, is one of the most crucial regions to preserve in neurosurgical intervention. The central sulcus is also a landmark of utmost importance for neurosurgeons. Although the arteries supplying the central region have been briefly described, their exact course has not been studied. The aim of the study is to establish the position and course of the central sulcus artery in relation to the central sulcus and its convolutions.

METHODS

Computer-assisted three-dimensional (3-D) anatomical reconstructions of the central area and of the central sulcus artery were performed with the aid of neuronavigational software in 13 patients operated at the Montreal Neurological Institute (MNI).

RESULTS

The central sulcus artery was coincident with the central sulcus and course(s) was almost similar on both hemispheres.

CONCLUSIONS

The knowledge of the exact course of the central sulcus artery is of paramount importance in cases of lesions or epileptic foci involving the central area. 3-D reconstruction with neuronavigation has proven to be a reproducible and reliable technique to provide the surgeon with the necessary surgical topographic anatomy of the central sulcus artery and central area.

SURGERY OF INTRINSIC CEREBRAL TUMORS

TUMORS AND OTHER structural lesions located with and adjacent to the cerebral cortex present certain challenges in terms of the overall management and design of surgical strategies. This comprehensive analysis attempts to define the current understanding of cerebral localization and function and includes the latest advances in functional imaging, as well as surgical technique, including localization of tumors and neurophysiological mapping to maximize extent of resection while minimizing morbidity. Finally, it remains to be seen whether or not stimulation mapping will be the most useful way to identify function within the cortex in the future. Another potential paradigm would be to actually record baseline oscillatory rhythms within the cortex and, following presentation of a given task, determine if those rhythms are disturbed enough to identify eloquent cortex as a means of functional localization. This would be a paradigm shift away from stimulation mapping, which currently deactivates the cortex, as opposed to identifying an activation function which identifies functional cortex.

Rater-dependent accuracy in predicting the spatial location of functional centers on anatomical MR images

OBJECTIVES

The determination of eloquent cortex is essential when planning neurosurgical approaches to brain lesions. This study examined the abilities of medical personnel of various backgrounds to predict the location of functional cortex using anatomical information provided by MR imaging.

PATIENTS AND METHODS

Neurosurgeons, neuroscientists, neuroradiologists, medical students and MR technologists viewed anatomical MR images acquired from patients with brain tumors and healthy controls. These five groups of raters were then asked to locate the primary motor hand, supplementary motor and primary auditory areas and their predictions were compared to fMRI data acquired from the same subjects.

RESULTS

The overall mean distance from the center of the fMRI activation was 2.38 cm. The neuroscientists performed the best and MR technologists performed the worst (mean distance from center of 1.83 and 3.04 cm, respectively, p<0.05). The difference between patients and controls was not significant. The mean distance by ROI was primary motor hand 2.03 cm, auditory area 2.06 cm and supplementary motor area 3.18 cm (p<0.05). Raters also performed best in the medial-lateral direction, compared to superior-inferior and anterior-posterior directions (mean distances from center 0.42, 1.04 and 1.81 cm, respectively). Finally, the approximate minimum fields of view necessary to capture the entire fMRI activations using the raters' predictions ranged from 5 to 15 cm, or 3 to 12 cm larger than the fMRI activations.

CONCLUSION

Medical personnel of various training perform poorly when using only anatomical information to predict the location of functional areas of cortex.

Surgery of the anterior part of the frontal lobe and of the central region: normative morphometric data based on magnetic resonance imaging

Modern magnetic resonance imaging (MRI) techniques have improved the planning of surgery to remove lesions in or around the frontal lobe. Since MRI-based morphometric analyses of the anterior part of the frontal lobe and the central region as part of it have not yet been performed, the present study was undertaken to obtain relative normative morphometric data. Median sagittal MRI scans from 53 magnetization prepared rapid acquisition gradient echo (MPRAGE) sequences of individual brains without pathological lesions were analyzed. The AC-PC line (anterior commissure-posterior commissure line) with vertical lines through the AC and PC were chosen as reference lines. Measurements of the anterior part of the frontal lobe included distances between different landmarks (frontal pole, tuberculum sellae, AC, outer point and inner surface of the genu of the corpus callosum, and the cortex at this level). For the measurements around the central region distances were obtained from the following landmarks: coronal suture, central sulcus, marginal sulcus, intersection point of the vertical line through the PC with the cortex, and PC. Knowledge of these distances will allow exact planning of surgical approaches to the anterior part of the frontal lobe, for example, the subfrontal or anterior interhemispheric approach and surgery around the central region.

A rapid fMRI task battery for mapping of visual, motor, cognitive, and emotional function

A set of sensory, motor, cognitive, and emotional tasks were combined in a simple, rapid-presentation task battery and tested on a group of 31, normal, healthy subjects aged 22 to 76. Five tasks were selected on the basis of widespread use in fMRI and their ability to produce robust and reliable regional activations. They were (1) a visual task designed to activate the occipital cortex; (2) a bimanual motor task designed to activate motor areas; (3) a verb generation task designed to activate speech processing areas; (4) an n-back task designed to activate areas associated with working memory and executive function; and (5) an emotional pictures task designed to provoke strong emotional responses that typically activate limbic structures. Most of the tasks produced reliable activations in individual subjects, and assessments of the distribution and reliability of individual subject activations in each targeted area are provided. The emotional pictures task did not demonstrate adequate sensitivity in a priori target regions, only in the a posteriori defined inferior temporal region. Age- and gender-specific differences were found in the activation patterns for both the cognitive and emotional tasks. The battery provides a prescribed means for researchers to obtain reliable functional localizers within 20-25 min of scanning, which can be used to support more elaborate mapping studies of brain function. The dataset can also serve as a reliability metric for new fMRI laboratories and novice investigators seeking to test their acquisition and analysis techniques with minimal time investment and expense.

PET and SPECT in low-grade glioma

Low-grade gliomas (LGG) account for 30-40% of all gliomas and are primarily treated with surgery. Since both timing and use of other oncological treatments in LGG are a matter of controversy, there has been a constantly increasing demand to characterize these often slowly growing neoplasms with functional imaging methods, such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). PET and SPECT yield information on growth rate and heterogeneity of LGG and are especially useful in follow-up since metabolic changes tend to precede structural changes detected with structure-based imaging methods. Furthermore, for planning of LGG surgery or radiotherapy coregistration of functional images with CT and MRI is invaluable. This is increasingly performed with a new generation of hybrid scanners with integrated PET or SPECT and CT.

Resection of parietal lobe gliomas: incidence and evolution of neurological deficits in 28 consecutive patients correlated to the location and morphological characteristics of the tumor

OBJECT

The goal of this study is to report the incidence and clinical evolution of neurological deficits in patients who underwent resection of gliomas confined to the parietal lobe.

METHODS

Patient demographics, findings of serial neurological examinations, tumor location and neuroimaging characteristics, extent of resection, and surgical outcomes were tabulated by reviewing inpatient and office records, as well as all pre- and postoperative magnetic resonance (MR) images obtained in 28 consecutive patients who underwent resection of a glial neoplasm found on imaging studies to be confined to the parietal lobe. Neurological deficits were correlated with hemispheric dominance, location of the lesion within the superior or inferior parietal lobules, subcortical extension, and involvement of the postcentral gyrus. The tumors were located in the dominant hemisphere in 18 patients (64%); had a mean diameter of 39 mm (range 14-69 mm); were isolated to the superior parietal lobule in six patients (21%) and to the inferior parietal lobule in eight patients (29%); and involved both lobules in 14 patients (50%). Gross-total resection, documented by MR imaging, was achieved in 24 patients (86%). Postoperatively, nine patients (32%) experienced new neurological deficits, whereas seven (25%) had an improvement in their preoperative deficit. A correlation was noted between larger tumors and the presence of neurological deficits both before and after resection. Postoperatively higher-level (association) parietal deficits were noted only in patients with tumors involving both the superior and inferior parietal lobules in the dominant hemisphere. At the 3-month follow-up examination, five of nine new postoperative deficits had resolved.

CONCLUSIONS

Neurological deterioration and improvement occur after resection of parietal lobe gliomas. Parietal lobe association deficits, specifically the components of Gerstmann syndrome, are mostly associated with large tumors that involve both the superior and inferior parietal lobules of the dominant hemisphere. New hemineglect or sensory extinction was not noted in any patient following resection of lesions located in the nondominant hemisphere. Nevertheless, primary parietal lobe deficits (for example, a visual field loss or cortical sensory syndrome) occurred in patients regardless of hemispheric dominance.

Neuroimaging of Metastatic Brain Disease

This review discusses imaging techniques for the diagnosis, treatment, and monitoring of brain metastases. It assesses the various modalities on the basis of their respective advantages and limitations. Recent advances in imaging technologies provide evaluation that is more accurate for tumor localization, morphology, physiology, and biology. When used in combination, these technologies provide clinicians with a powerful diagnostic and prognostic tool for managing metastatic brain disease.

Preoperative mapping of cortical motor function: prospective comparison of functional magnetic resonance imaging and [15O]-H2O-positron emission tomography in the same co-ordinate system

BACKGROUND

Two of the most widely accepted approaches to map eloquent cortical areas preoperatively are positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). As yet, no study has compared these two modalities within the same frame of reference in tumour patients.

AIM

We employed [15O]-H2O-PET and fMRI in patients undergoing presurgical evaluation and compared the results with those obtained by direct electrical cortical stimulation (DECS).

METHODS

Twenty-five patients with tumours of different aetiology near the central region were investigated. fMRI and PET were processed using the same methods, i.e. statistical parametric mapping (SPM) without anatomical normalization, and transformed into the same frame of reference.

RESULTS

fMRI activity was found in more cranial and lateral sections, i.e. closer to the brain surface, in comparison with PET, which demonstrated parenchymal activation. The mean localization difference between fMRI and PET was 8.1 +/- 4.6 mm (range, 2-18 mm). fMRI and [15O]-H2O-PET could reliably identify the central sulcus, as demonstrated by DECS.

CONCLUSIONS

fMRI and [15O]-H2O-PET demonstrate comparable results and are sensitive and reliable tools to map the central region, especially in cases of infiltrating brain tumours. However, fMRI is more prone to artefacts, such as the visualization of draining veins, which may explain the more cranial and lateral activation visualized by fMRI, whereas PET depicts capillary perfusion changes and therefore shows activation closer to the parenchyma.

Preoperative blood oxygen level-dependent functional magnetic resonance imaging in patients with primary brain tumors: clinical application and outcome

OBJECTIVE

This study sought to evaluate the ability of blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to successfully identify functional cortical areas in patients with primary brain tumors, to evaluate the use of the fMRI results in presurgical planning, and to assess the functional outcome of the patients with respect to the functional maps obtained with fMRI.

METHODS

The study included 25 consecutive preoperative fMRI sessions in patients with primary brain tumors in or near sensorimotor and/or language cortices. All fMRI paradigms were analyzed and rated according to the degree of success. Several distances between tumor and functional cortex as delineated with BOLD fMRI were measured to assess the topographic relationship between these two structures. Pre- and postoperative neurological statuses were obtained from the patients' journals.

RESULTS

Acquisition of BOLD fMRI images was successful in 80% of the cases. The primary cause of unsuccessful fMRI was echo-planar imaging signal voids that were the result of previous craniotomy; the secondary cause was excessive motion. The neurosurgeons used the fMRI results for preoperative planning in 75% of the cases in which fMRI was successful. The risk of postoperative loss of function tested with fMRI was significantly lower when the distance between tumor periphery and BOLD activity was 10 mm or more.

CONCLUSION

The majority of patients with primary brain tumors were capable of satisfactorily performing the fMRI paradigms, and the information obtained was used in the preoperative planning. A distance of 10 mm or more between the functional cortex, as delineated with fMRI, and the tumor significantly reduced the risk of postoperative loss of function.

Fully automated localization of the human primary somatosensory cortex in one minute by functional magnetic resonance imaging

A clinical functional magnetic resonance imaging (fMRI) protocol based on a fully automated tactile stimulation was optimized in 10 right-handed volunteers at 1.5 T for minimum scan time, high BOLD-signals and robust localization of the primary somatosensory cortex (S1) by systematically varying the applied block design. All volunteers had six different fMRI measurements of 5 stimulation/baseline cycles each with equal block duration that was changed between the measurements from 6 to 30 s. Data sets of 4, 3 and 2 cycles were generated post hoc resulting in a total of 240 data sets that were evaluated individually for BOLD-signal intensity (dS%), correlation to the hemodynamic reference function (r) and Euclidean coordinates (x, y, z). The protocol with 5 cycles, a block duration of 6 s and a total scan time of 66 s provided the best BOLD-signal characteristics (dS% = 1.15, r = 0.78). Compared to the mean scan time of other clinical fMRI protocols (174 s) a reduction of 62% was achieved.

Evaluating requirements for spatial resolution of fMRI for neurosurgical planning

The unambiguous localization of eloquent functional areas is necessary to decrease the neurological morbidity of neurosurgical procedures. We explored the minimum spatial resolution requirements for functional magnetic resonance imaging (fMRI) data acquisition when brain mapping is used in neurosurgical planning and navigation. Using a 1.5 Tesla clinical MRI scanner, eight patients with brain tumors underwent fMRI scans using spatial resolution of approximately 4 x 4 x 4 mm(3) to map the eloquent motor and language areas during the performance of cognitive/sensorimotor tasks. The fMRI results were then used intra-operatively in an open MRI system to delineate eloquent areas. Retrospectively, activation patterns were visually inspected by a neurosurgeon to determine qualitatively whether ambiguity with respect to the activation boundaries, due to low spatial resolution, could be of potential significance for surgical guidance. A significant degree of ambiguity in both the extent and shape of activation was judged to be present in data from six of the eight patients. Analysis of fMRI data at multiple resolutions from a normal volunteer showed that at 3 mm isotropic resolution, eloquent areas were better localized within the gray matter although there was still some potential for ambiguity caused by activations appearing to cross a sulcus. The data acquired with 2-mm isotropic voxels significantly enhanced the spatial localization of activation to within the gray matter. Thus, isotropic spatial resolution on the order of 2 x 2 x 2 mm(3), which is much higher than the resolutions used in typical fMRI examinations, may be needed for the unambiguous identification of cortical activation with respect to tumors and important anatomical landmarks.

Focused high frequency repetitive transcranial magnetic stimulation for localisation of the unexposed primary motor cortex during brain tumour surgery

OBJECTIVES

To investigate if intraoperative focused high frequency repetitive transcranial magnetic stimulation (rTMS) can localise the primary motor cortex without exposure of the cortical surface.

METHODS

A high frequency train (357 Hz) of four suprathreshold magnetic stimuli was delivered transcranially to the region of the rolandic area during brain tumour operations in 12 patients. To induce a focal magnetoelectric field, the flat figure of eight coil (outer diameter of each loop 7 cm) was used. Motor evoked potentials (MEP) were recorded in eight muscles of the upper and lower contralateral extremities. The first stimulation site was 2.5 cm behind the bregma, the second site 2 cm, and the third site 4 cm dorsal to the first stimulation site. If no MEP were obtainable, stimulation was repeated in anteroposterior direction at more laterally located sites. Using neuronavigation, each positive stimulation site was correlated with the underlying cortical anatomy.

RESULTS

Stimulation was performed at a total of 42 sites (in two patients, maximum stimulation at the three initial sites failed to evoke a motor response). In four patients, MEP were obtained only from one stimulation site. This site exactly overlayed the primary motor cortex. In eight patients, MEP could be elicited from more than one stimulation site. In seven of the eight patients, the site from which MEP with peak amplitudes were elicited, corresponded to the primary motor cortex. In total, the primary motor cortex was correctly identified on the basis of electrophysiological findings in 11 of 12 patients (92 %). In two patients, only the more lateral stimulation sites permitted MEP recording.

CONCLUSION

Intraoperative focused rTMS is highly sensitive for localisation of the primary motor cortex. Focused rTMS as a localising instrument alleviates the need of motor cortex exposure and, thereby, can contribute to minimise the surgical approach to brain tumours in the rolandic area.

Functional magnetic resonance imaging for brain mapping in neurosurgery

One of the most pertinent applications of the principle primum non nocere (first do no harm) is in the optimization of neurosurgical procedures for patients with resectable lesions. The gold standard for identifying eloquent areas of the brain to be avoided in resections is direct cortical stimulation and somatosensory evoked potential monitoring, which is itself an invasive, cumbersome and difficult technique for mapping these areas. Functional magnetic resonance imaging shows great promise as a viable noninvasive alternative to invasive mapping as well as significant current clinical utility in cases in which it cannot yet fully supplant cortical stimulation methods. Ongoing work is directed toward overcoming technical limitations, improved mapping of complex functions such as language and memory, and mapping of white matter tracts.

Presurgical fMRI evaluation of cerebral reorganization and motor deficit in patients with tumors and vascular malformations

The aim of this fMRI study was to evaluate the motor reorganization (cerebral plasticity) and the risk of motor deficit in patients presenting with tumors and vascular malformations, within the framework of their pre-surgical planning. Functional MR imaging data was obtained from 17 patients. Ten patients (seven with tumors and three with vascular malformations) presented with motor reorganization. The results of the present study suggest that the evaluation of the cerebral reorganization is an essential step in predicting the risk of motor deficit in patients having surgical indication for treatment. Furthermore, the cerebral reorganization constitutes an important factor for surgical decision.

Integration of sulcal and functional information for multimodal neuronavigation

OBJECT

The authors present the use of cortical sulci, segmented from magnetic resonance (MR) imaging, and functional data from functional (f)MR imaging and magnetoencephalography (MEG) in the image-guided surgical management of lesions adjacent to the sensorimotor cortex.

METHODS

In an initial set of 11 patients, sulci near lesions were automatically segmented from MR imaging data sets, then MEG and fMR imaging examinations were performed. Relevant functional information was preoperatively interpreted and selected from MEG and fMR imaging and subsequently transferred to the navigation system for selected sulci. A neuronavigation system consisting of a surgical microscope with enhanced reality overlay display was used. Data were displayed as contours on the cut-plane images of a stereotactic workstation and as contours on the overlay screen of the head-up display within the optical path of the right eyepiece of the surgical microscope.

CONCLUSIONS

This method, in which both sulcal and functional mapping are used for surgery planning and neuronavigation, provides helpful information. It is a promising procedure for the treatment of patients who harbor lesions in areas around the eloquent cortex.

Diffusion imaging in brain tumors

Diffusion-weighted imaging is of limited value in the MR imaging diagnosis of various tumor pathologies, except in differentiating between dermoids/epidermoids and arachnoid cysts. Diffusion tractography, on the other hand, allows accurate depiction of important white-matter tracts adjacent to brain tumors. This technique uses data derived from diffusion tensor imaging.

Characterization of BOLD-fMRI signal during a verbal fluency paradigm in patients with intracerebral tumors affecting the frontal lobe

Previous studies have indicated that the BOLD-fMRI signal can be modified by tumor processes in close vicinity to functional brain areas. This effect has been investigated primarily for the perirolandic area but there is only a limited number of studies concerning frontal cortical regions. Therefore, the aim of the current study was to characterize BOLD-fMRI signal and activation patterns in patients with frontal brain tumors while performing a verbal fluency task. Six patients (ages 31-56 years) suffering from frontal (5 left sided and 1 right sided) intracerebral tumors were examined with fMRI while performing a verbal fluency task in a blocked paradigm design. Eight healthy volunteers served as the control group. The patients (5 right and 1 left handed) demonstrated left frontal activation which could be clearly located outside the tumor area and adjacent edema with varying degrees of additional right frontal activation. In the predominant left frontal activation cluster, the mean voxel based z-score and cluster size were not statistically different between patients and controls. The present fMRI study is indicating that language related BOLD signal changes in the frontal cortex of patients with tumors close to functional areas were comparable to the signal in normal controls. Additionally, the temporal hemodynamic response characteristic was comparable in both groups. This is an important finding consistent with PET results and corroborates the feasibility of functional mapping approaches in patients with tumors affecting the frontal lobe. Additional studies investigating alterations of the hemodynamic response depending on tumor location and histology are required in order to further elucidate the association between pathophysiology and BOLD fMRI signal.

Multimodal anatomic, functional, and metabolic brain imaging for tumor resection

OBJECTIVE

Improvement of neurosurgical techniques with a more detailed description of brain tumors and their functional environment.

METHODS

We performed: (1) anatomical magnetic resonance imaging (MRI) for reference, (2) functional sequences dedicated to the adjacent cortical structures (sensorimotor, visual, language paradigms), and (3) thallium 201 cerebral tomoscintigraphy to visualize active tumor invasion. Data were transferred to a workstation for automatic registration.

RESULTS

All data were combined into one synthetic image showing the foci of high proliferative activity, which have to be completely resected, and the peritumoral functional structures, which have to be spared in order to minimize postoperative sequelae. This trimodal image is entered into a surgical neuronavigation computer for preoperative planning in order to outline tumoral target and functional risk areas. All this information is displayed in the operative microscope (Zeiss MKM) optically linked to MR images. This multimodality technique diminishes operative time by reducing electrocorticography and improves the operative short-term outcome.

CONCLUSION

Multimodal imaging is useful for optimization of neurosurgical tumor resection.

Task-related signal decrease on functional magnetic resonance imaging

An atypical pattern of signal change was identified on functional magnetic resonance (fMR) imaging in pathologic patients. Three normal volunteers and 34 patients with pathologic lesions near the primary motor cortex underwent fMR imaging with echo-planar imaging while performing a hand motor task. Signal intensities were evaluated with the z-score method, and the time course and changes of the signal intensity were calculated. Nine of the 34 patients with pathologic lesions displayed a significant task-related signal reduction in motor-related areas. They also presented a conventional task-related signal increase in other motor-related areas. The time courses of the increase and decrease were the inverse of each other. There was no significant difference between rates of signal increase and decrease. Our findings suggest that this atypical signal decrease is clinically significant, and that impaired vascular reactivity and altered oxygen metabolism could contribute to the task-related signal reduction. Brain areas showing such task-related signal decrease should be preserved at surgery.