Multiple subpial transections and magnetic resonance imaging.

INTRODUCTION: Multiple subpial transection (MST) has been applied to the treatment of refractory epilepsy when epileptogenic zone involves eloquent areas since 1989. However, there is a lack of data evaluating the effect of this surgical technique on the cortex as measured by Magnetic Resonance Imaging (MRI). PATIENTS AND METHODS: Ten consecutive patients (3F/7M, average age: 18.5 years) were operated on using radiating MST (average: 39; min: 19, max: 61) alone (n=3) or associated with another technique (n=7). Seven patients underwent a post-operative 3.0T MRI while 3 had a 1.5T MRI. Three patients had an early post-operative MRI and 7 a late MRI, among which 3 previously had an intraoperative MRI. RESULTS: The MR sequences that allowed the best assessment of MST-induced changes were T2 and T2*. The traces of MST are more visible on late MRI. These discrete non-complicated stigmas of MST were observed in all 10 studied patients: on the intraoperative MRI they are seen as micro-hemorrhagic spots (hypo-T2), on the early postoperative MRI as a discreet and limited cortical edema whether associated or not with micro-hemorrhagic spots and on the late MRI as liquid micro-cavities (hyper-T2) surrounded with a fine border of hemosiderin. CONCLUSIONS: MST-induced cerebral lesions are best visualized in T2-sequences, mainly on the late postoperatively MRIs. On all the MRI examinations in this study, the MST are only associated with limited modifications of the treated cortical regions.

Cortical activation resulting from the stimulation of periodontal mechanoreceptors measured by functional magnetic resonance imaging (fMRI).

OBJECTIVE: To describe the normal cortical projections of periodontal mechanoreceptors. MATERIAL AND METHODS: A device using von Frey filaments delivered 1-Hz punctate tactile stimuli to the teeth during fMRI. In a block design paradigm, tooth (T) 11 and T13 were stimulated in ten volunteers and T21 and T23 in ten other subjects. Random-effect group analyses were performed for each tooth, and differences between teeth were examined using ANOVA. RESULTS: The parietal operculum (S2) was activated bilaterally for all teeth; the postcentral gyrus (S1) was activated bilaterally for T21 and T23 and contralaterally for T11 and T13. In the second-level analysis including the four teeth, we found five clusters: bilateral S1 and S2, and left inferior frontal gyrus, with no difference between teeth in somatosensory areas. However, the ANOVA performed on the S1 clusters found separately in each tooth showed that S1 activation was more contralateral for the canines. CONCLUSION: One-hertz mechanical stimulation activates periodontal mechanoreceptors and elicits bilateral cortical activity in S1 and S2, with a double representation in S2, namely in OP1 and OP4. CLINICAL RELEVANCE: The cortical somatotopy of periodontal mechanoreceptors is poorly described. These findings may serve as normal reference to further explore the cortical plasticity induced by periodontal or neurological diseases.

Mild cognitive impairment: differential atrophy in the hippocampal subfields.

BACKGROUND AND PURPOSE: Hippocampus volumetry is a useful surrogate marker for the diagnosis of Alzheimer disease, but it seems insufficiently sensitive for the aMCI stage. We postulated that some hippocampus subfields are specifically atrophic in aMCI and that measuring hippocampus subfield volumes will improve sensitivity of MR imaging to detect aMCI. MATERIALS AND METHODS: We evaluated episodic memory and hippocampus subfield volume in 15 patients with aMCI and 15 matched controls. After segmentation of the whole hippocampus from clinical MR imaging, we applied a new computational method allowing fully automated segmentation of the hippocampus subfields. This method used a Bayesian modeling approach to infer segmentations from the imaging data. RESULTS: In comparison with controls, subiculum and CA2-3 were significantly atrophic in patients with aMCI, whereas total hippocampus volume and other subfields were not. Total hippocampus volume in controls was age-related, whereas episodic memory was the main explanatory variable for both the total hippocampus volume and the subfields that were atrophic in patients with aMCI. Segmenting subfields increases sensitivity to diagnose aMCI from 40% to 73%. CONCLUSIONS: Measuring CA2-3 and subiculum volumes allows a better detection of aMCI.

[Intramedullary tumours and pseudotumours]. / Moelle épinière tumorale et pseudo-tumorale.

Swelling of the spinal cord and/or enhancement after intravenous gadolinium administration are not always specific features of intramedullary tumour. These may also be seen in association with several diseases of inflammatory, infectious, granulomatous or vascular origin. A tumour is characterized by its sagittal location, axial topography: central, lateral or exophytic, its size and size of the spinal canal, macroscopic components: calcium, fat, methemoglobin, melanin, hemosiderin, vascular pedicle, cystic component, enhancement after intravenous gadolinium administration, effect on the spinal cord tracts and edema. Characteristics: astrocytoma is lateral and infiltrative, ependymoma is central with white matter tract displacement and hemosiderin cap, hemangioblastoma is postero-lateral and shows enhancement with a vascular pedicle, metastases are very edematous or leptomeningeal in location.

How to measure olfactory bulb volume and olfactory sulcus depth?

In combination with psychophysical testing and electrophysiological studies, magnetic resonance imaging plays a role in the clinical evaluation of patients with an olfactory dysfunction. Quantitative measurements of olfactory bulb volume and of olfactory sulcus depth, and the morphological depiction of structural abnormalities, make synergistic contributions to the accurate radiological diagnosis of smell dysfunction. Moreover, the plasticity of our olfactory system can be demonstrated by temporal changes in OB volumetric measurements. In this paper, we provide an outline of how to measure olfactory bulb volume and olfactory sulcus depth, with numerous illustrative cases of patients with congenital anosmia, post-infectious or posttraumatic olfactory loss and sinonasal-related olfactory dysfunction.

Intraoperative 3T MR imaging for spinal cord tumor resection: feasibility, timing, and image quality using a "twin" MR-operating room suite.

We assessed feasibility, safety, and timing of an original intraoperative MR procedure in 3 cases of resection of spinal cord glioma by using a clinical 3T MR system connected to an adjacent operating room in a design being coined "twin" or "dual" MR-operating room suite.

[Central nervous system involvement in Wegener's granulomatosis]. / Atteinte cérébrale au cours d'une maladie de Wegener.

INTRODUCTION: Wegener's granulomatosis (WG) is a systemic necrotizing vasculitis associated with c-ANCA antibodies. The involvement of the central nervous system in WG is uncommon and usually caused by in situ vasculitis, intracranial granuloma formation or contiguous invasion from extracranial sites. CASE REPORT: Here, we report on a tumour-like expansion of a severe nasosinusal WG into the brain, which was confirmed by brain biopsy examination. CONCLUSION: The positivity of positron emission tomography in our observation supports the potential role of such functional imaging in the staging, as well as in the follow-up of WG.

[Safety and efficacy of multiple subpial transections: report of a consecutive series of 30 cases]. / Sécurité et efficacité des trans-sections sous-piales multiples: analyse d'une série consécutive de 30 patients.

PURPOSE: To present our results using multiple subpial transections (MST) for the treatment of pharmacologically refractory epilepsy (PRE) with epileptogenic foci in eloquent areas. METHOD: Between January 2003 and March 2006, we treated 33 patients with PRE with epileptogenic foci in eloquent areas by MST "in rays", either isolated (MSTs group) or completing resection or disconnection of other cortical areas (MST+ group). Our first 30 patients had a follow-up of at least 24 months: eight in the MSTs group and 22 in the MST+ group. Four postoperative grades were distinguished based on a modified Engel classification: seizure-free (100% seizure reduction equals to Grade I), substantial significant seizure reduction (75% to 99% seizure reduction equals to Grade II), moderate significant reduction (50% to 74% seizure reduction equals to Grade III) and finally no significant reduction (seizure reduction less than 50% equals to Grade IV). RESULTS: In the MSTs group, two patients (25%) were in grade I and five (62%) in grade II or III. In the MST+ group, six patients (27%) were in grade I and 13 (59%) in grade II or III. All patients showed some seizure reduction and some improvement in behavior or cognitive function with no permanent neurological deficit. CONCLUSION: This series supports the notion that multiple subpial transections are associated with a significant seizure reduction (in 86.6% of the cases reported herein) and that the risk of permanent neurological deficit can be very low.

Ischemic cerebral lesions after carotid surgery and carotid stenting.

OBJECTIVES: To evaluate the risk of new ischemic cerebral lesions after carotid endarterectomy and carotid stenting and their clinical significance. METHODS: Prospective and non-randomized single-center study including 121 patients with symptomatic and asymptomatic significant carotid stenosis. 60 patients were treated by surgery and 61 treated by carotid stenting. Stenting was restricted to patients at high risk for surgery. Neurological examination and Diffusion-Weighted Cerebral Magnetic Resonance (DW-MRI) were performed before and after each procedure. The presence, location and volume of new cerebral lesions were determined. RESULTS: In the surgical group, 2 minor strokes were registered. DW-MRI showed new lesions in 7 patients (11.6%). All except one were located in the ipsilateral anterior circulation. In the stenting group, 1 minor stroke and 1 occurrence of quadranopsia were registered. DW-MRI showed new lesions in 26 patients (42.6%). 10 of these patients (38.4%) had lesions in the contralateral hemisphere and 7 patients (26.9%) in the posterior circulation. Deficits are found in patients with higher lesion volumes. CONCLUSIONS: Cerebral ischemic lesions are significantly (p<0.0001) more frequent after carotid stenting than after endarterectomy. The majority of these lesions have no immediate clinical implication, but more specific tests are needed to evaluate their exact significance.

Seizure focus affects regional language networks assessed by fMRI.

OBJECTIVE: To investigate the degree of language dominance in patients with left and right hemisphere seizure foci compared to normal volunteers using a fMRI reading comprehension task. METHODS: Fifty patients with complex partial epilepsy, aged 8 to 56 years and 33 normal volunteers, aged 7 to 34 had fMRI (1.5 T) and neuropsychological testing. Participants silently named an object described by a sentence compared to a visual control. Data were analyzed with region of interest (ROI) analysis based on t maps for inferior frontal gyrus (IFG), midfrontal gyrus (MFG), and Wernicke area (WA). Regional asymmetry indices (AIs) were calculated [(L - R)/(L + R)]; AI > 0.20 was deemed left dominant and AI < 0.20 as atypical language. RESULTS: Left hemisphere focus patients had a higher likelihood of atypical language than right hemisphere focus patients (21% vs 0%, chi2 < 0.002). Left hemisphere focus patients, excluding those with atypical language, had lower regional AI in IFG, MFG, and WA than controls. Right hemisphere focus patients were all left language dominant and had a lower AI than controls in WA and MFG, but not for IFG. AI in MFG and WA were similar between left hemisphere focus/left language patients and right hemisphere focus patients. Patients activated more voxels than healthy volunteers. Lower AIs were attributable to greater activation in right homologous regions. Less activation in the right-side WA correlated with better verbal memory performance in right focus/left hemisphere-dominant patients, whereas less strongly lateralized activation in IFG correlated better with Verbal IQ in left focus/left hemisphere-dominant patients. CONCLUSIONS: Patients had lower asymmetry indices than healthy controls, reflecting increased recruitment of homologous right hemisphere areas for language processing. Greater right hemisphere activation may reflect greater cognitive effort in patient populations, the effect of epilepsy, or its treatment. Regional activation patterns reflect adaptive efforts at recruiting more widespread language processing networks that are differentially affected based on hemisphere of seizure focus.

Comparative overview of brain perfusion imaging techniques.

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are: Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Xenon-enhanced Computed Tomography (XeCT), Dynamic Perfusion-computed Tomography (PCT), Magnetic Resonance Imaging Dynamic Susceptibility Contrast (DSC), Arterial Spin-Labeling (ASL), and Doppler Ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow (CBF) or volume (CBV). All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks. This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview, established by consensus among specialists of the various techniques. For clinicians, this paper should offers a clearer picture of the pros and cons of currently available brain perfusion imaging techniques, and assist them in choosing the proper method in every specific clinical setting.

Assessment of brain perfusion with MRI: methodology and application to acute stroke.

We review the methodology of brain perfusion measurements with MRI and their application to acute stroke, with particular emphasis on the work awarded by the 6th Lucien Appel Prize for Neuroradiology. The application of the indicator dilution theory to the dynamic susceptibility-weighted bolus-tracking method is explained, as is the approach to obtaining quantitative measurements of cerebral blood flow (CBF) and volume (CBV). Our contribution to methodological developments, such as CBV measurement with the frequency-shifted burst sequence, development of the PRESTO sequence, comparison of different deconvolution methods and of spin- and gradient-echo sequences, and the validation of MRI measurements against positron emission tomography is summarised. The pathophysiology of brain ischaemia and the role of neuroimaging in the setting of acute stroke are reviewed, with an introduction to the concepts of ischaemic penumbra and diffusion/perfusion mismatch. Our work on the determination of absolute CBF and CBV thresholds for predicting the area of infarct growth, identification of the best perfusion parameters (relative or absolute) for predicting the area of infarct growth and the role of MR angiography is also summarised. We conclude that MRI is a very powerful way to assess brain perfusion and that its use might help in selecting patients who will benefit most from treatment such as thrombolysis.

[MRI of closed head injury]. / IRM et traumatismes crânio-encéphaliques fermés.

The superiority of MR imaging to demonstrate the presence of intra- or extra-axial hemorrhage or edematous lesions, including axonal injuries, following closed head trauma has been proven over the last 15 years. CT remains the initial imaging modality in the evaluation of these patients because it is easier to obtain and allows detection of lesions requiring immediate surgical management. However, MRI should replace CT in patients with moderate to mild trauma in order to better precise the extent and degree of injuries, especially in a context of litigation. MRI could also be used following CT to further assess patients following severe trauma for prognosis purposes and better classification of traumatic injuries as well as therapeutic management.

Language dominance in partial epilepsy patients identified with an fMRI reading task.

BACKGROUND: fMRI language tasks readily identify frontal language areas; temporal activation has been less consistent. No studies have compared clinical visual judgment to quantitative region of interest (ROI) analysis. OBJECTIVE: To identify temporal language areas in patients with partial epilepsy using a reading paradigm with clinical and ROI interpretation. METHODS: Thirty patients with temporal lobe epilepsy, aged 8 to 56 years, had 1.5-T fMRI. Patients silently named an object described by a sentence compared to a visual control. Data were analyzed with ROI analysis from t-maps. Regional asymmetry indices (AI) were calculated ([L-R]/[L+R]) and language dominance defined as >0.20. t-Maps were visually rated by three readers at three t thresholds. Twenty-one patients had intracarotid amobarbital test (IAT). RESULTS: The fMRI reading task provided evidence of language lateralization in 27 of 30 patients with ROI analysis. Twenty-five were left dominant, two right, one bilateral, and two were nondiagnostic; IAT and fMRI agreed in most patients, three had partial agreement, none overtly disagreed. Interrater agreement ranged between 0.77 to 0.82 (Cramer V; p < 0.0001); agreement between visual and ROI reading with IAT was 0.71 to 0.77 (Cramer V; p < 0.0001). Viewing data at lower thresholds added interpretation to 12 patients on visual analysis and 8 with ROI analysis. CONCLUSIONS: An fMRI reading paradigm can identify language dominance in frontal and temporal areas. Clinical visual interpretation is comparable to quantitative ROI analysis.

Apparent diffusion coefficient measurements within intracranial epidermoid cysts in six patients.

The purpose was to determine whether a strong decrease in apparent diffusion coefficient (ADC) within epidermoid cysts (ECs) is actually responsible for their bright signal intensity on diffusion-weighted (DW) trace images. We studied six patients with surgically proven ECs in whom ADC calculation from T2-weighted DW-EPI-SE data were performed within the ECs and within the deep white matter and cerebrospinal fluid (CSF) as references. All ECs displayed highest signal intensity on the DW trace images. ADC values ranged from 1,280 to 807 x 10(-6) mm(2)/s within cysts (with a mean value of 1,070), from 849 to 698 x 10(-6) mm(2)/s within white matter (with a mean value of 764) and from 3,370 to 2,980 x 10(-6) mm(2)/s within CSF (with a mean value of 3,185). ECs exhibited slightly higher ADC values than white matter, and not the strongly decreased ones which would have been expected if diffusion-weighting were the prominent mechanism for bright signal intensity of the ECs on DW images. However, the EC ADC values are much lower than those of the CSF. Other mechanisms must therefore be involved, i.e. the T2 shine-through effect. Reduced ADC is not the only explanation of the EC bright signal intensity on the DW trace images.

Is there an apparent diffusion coefficient threshold in predicting tissue viability in hyperacute stroke?

BACKGROUND AND PURPOSE: Rapid and precise identification of the penumbra is important for decision-making in acute stroke. We sought to determine whether an early and moderate decrease in the apparent diffusion coefficient (ADC) may help to identify, within the diffusion/perfusion (DWI/PWI) mismatch, those areas that will eventually evolve toward infarction. METHODS: We reviewed 48 patients not treated by thrombolytics who had a DWI/PWI within 6 hours after onset, with infarct evolution documented by follow-up magnetic resonance on days 2 to 4. We calculated absolute values for ADC and the ADC ratio (ADCr) in (1) the initial DWI hypersignal; (2) the final volume of the infarct, ie, the follow-up fluid-attenuated inversion recovery abnormalities; (3) the infarct growth (IGR) area; and (4) the oligemic area (OLI) that remained viable despite initial hemodynamic disturbance. We tested the value of the ADC to predict tissue outcome by using discriminant analysis. RESULTS: ADC values were marginally but significantly decreased in the IGR area (ADC 782+/-82x10(-6) mm(2)/s, ADCr 0.94+/-0.08) compared with mirror values (P=0.01) and with OLI (ADC 823+/-41x10(-6) mm(2)/s, ADCr 0.99+/-0.07; P=0.001). Of all quantitative DWI and PWI parameters, the ADCr best discriminated between IGR and OLI (F(1,50)=13.6, cutoff=0.97, 64% sensitivity, 92% specificity) and between the final volume of infarct and OLI (F(1,83)=219, cutoff=0.91, 91% sensitivity, 100% specificity). CONCLUSIONS: A simple approach based on ADC alone may allow the identification of tissue at risk of infarction in acute-stroke patients.

Usefulness of magnetic resonance-derived quantitative measurements of cerebral blood flow and volume in prediction of infarct growth in hyperacute stroke.

BACKGROUND AND PURPOSE: The identification of the tissue at risk for infarction remains challenging in stroke patients. In this study, we evaluated the value of quantitative cerebral blood flow (CBF) and cerebral blood volume (CBV) measurements in the prediction of infarct growth in hyperacute stroke. METHODS: Fluid-attenuated inversion recovery (FLAIR), diffusion-weighted (DW), and gradient-echo echo-planar perfusion-weighted (PW) sequences were obtained in 66 patients within 6 hours of stroke onset; ischemia was confirmed on follow-up FLAIR images. We delineated the following: (1) the initial infarct on DW images, (2) the area of hemodynamic disturbance on mean transit time (MTT) maps, and (3) the final infarct on follow-up FLAIR images. MTT, CBF, and CBV were calculated in the following areas: area of initial infarct (INF), area of infarct growth (IGR, final minus initial infarct), the hemodynamically disturbed area that remained viable (OLI, hemodynamic disturbance minus final infarct), and all contralateral mirror regions. RESULTS: Compared with mirror regions, the MTT in abnormal areas was always prolonged. The respective mean+/-SD CBF and CBV values were as follows: for INF, 28+/-16 mL/min per 100 g and 6.9+/-2.7%; for IGR, 36+/-20 mL/min per 100 g and 8.9+/-3.1%; for OLI, 50+/-17 mL/min per 100 g and 11.2+/-3%; and for mirror regions, 64+/-23 mL/min per 100 g and 8.7+/-2.5%. The CBV and CBF values were significantly different between all abnormal areas (except for the CBF between INF and IGR). In the area of DW/PW mismatch, a combined CBF or CBV threshold of 35 or 8.2, respectively, predicted evolution to infarction with a sensitivity of 81% and a specificity of 76%. CONCLUSIONS: Quantitative measurements of CBF and CBV in hyperacute stroke may help to predict infarct growth and to select the subjects who will benefit from thrombolysis.

Cortical localization of reading in normal children: an fMRI language study.

BACKGROUND: fMRI provides a noninvasive means of identifying the location and organization of neural networks that underlie cognitive functions. OBJECTIVE: To identify, using fMRI, brain regions involved in processing written text in children. METHODS: The authors studied nine normal right-handed native English-speaking children, aged 10.2 years (range 7.9 to 13.3 years), with two paradigms: reading Aesop's Fables and "Read Response Naming" (reading a description of an object that was then silently named). Data were acquired using blood oxygen level-dependent fMRI. Group data were analyzed with statistical parametric mapping; individual data sets were analyzed with a region-of-interest approach from individual study t maps. The number of activated pixels was determined in brain regions and an asymmetry index (AI = [L - R]/[L + R]) calculated for each region. RESULTS: The authors found strong activation in the left middle temporal gyrus and left midfrontal gyrus and variable activation in left inferior frontal gyrus for both reading tasks in the group analysis (z > 5.5 to 9.1). All subjects had strong left-sided lateralization for both tasks in middle/superior temporal gyrus, inferior frontal gyrus, and middle frontal gyrus (AI = 0.76 to 1.0 for t = 4). Reading Fables activated twice as many pixels in temporal cortex as the Read Response Naming task; activation in dorsolateral prefrontal cortex was similar for both tasks. Small homologous right middle temporal region activation was seen with reading a fable. CONCLUSIONS: The neural networks that process reading appear to be lateralized and localized by middle to late childhood. Reading text paradigms may prove useful for identifying frontal and temporal language-processing areas and for determining language dominance in children experiencing epilepsy or undergoing tumor surgery.

Developmental aspects of pediatric fMRI: considerations for image acquisition, analysis, and interpretation.

Functional MRI provides a powerful means to identify and trace the evolution, development, and consolidation of cognitive neural networks through normal childhood. Neural network perturbations due to disease and other adverse factors during development can also be explored. Studies performed to date suggest that normal children older than 5 years show activation maps comparable to adults for similar cognitive paradigms. Minor differences in adult and pediatric activation maps may reflect age dependent strategies or maturation of cognitive networks. However, there are important physiologic and anatomic differences in children, varying with age, that may affect the acquisition, analysis, and interpretation of pediatric fMRI data. Differences between children and adult fMRI comparison studies may reflect technical aspects of data acquisition as much as developmental and brain maturation factors.