[Imaging Moya-Moya disease]. / Imagerie du Moya-Moya.

Moya-Moya disease is a rare arterial occlusive disease affecting the internal carotid artery and its branches. It is found in both pediatric and adult populations, and it may lead to severe clinical presentations such as stroke and intracranial hemorrhage. Several surgical procedures have been developed to improve its clinical outcome. Imaging techniques have a key role in management of Moya-Moya disease, as they are necessary for diagnosis, choice of treatment and follow-up. Although catheter angiography remains the diagnostic gold standard, and nuclear-medicine techniques best perform hemodynamic studies, less invasive imaging techniques have become efficient in serving these purposes. Conventional MRI and MR angiography, as well as MR functional and metabolic studies, are now widely used in each stage of disease management, from diagnosis to follow-up. CT scan and Doppler sonography may also help assess severity of disease and effects of treatment. The aim of this review is to clarify the utility, efficiency and latest developments of each imaging modality in management of Moya-Moya disease.

An update on brain imaging in transient ischemic attack.

Neuroimaging is critical in the evaluation of patients with transient ischemic attack (TIA) and MRI is the recommended modality to image an ischemic lesion. The presence of a diffusion (DWI) lesion in a patient with transient neurological symptoms confirms the vascular origin of the deficit and is predictive of a high risk of stroke. Refinement of MR studies including high resolution DWI and perfusion imaging using either MRI or CT further improve the detection of ischemic lesions. Rapid etiological work-up includes non-invasive imaging of cervical and intracranial arteries to search for symptomatic stenosis/occlusion associated with an increased risk of stroke.

MR screening of candidates for thrombolysis: How to identify stroke mimics?

Stroke mimics account for up to a third of suspected strokes. The main causes are epileptic deficit, migraine aura, hypoglycemia, and functional disorders. Accurate recognition of stroke mimics is important for adequate identification of candidates for thrombolysis. This decreases the number of unnecessary treatments and invasive vascular investigations. Correctly identifying the cause of symptoms also avoids delaying proper care. Therefore, this pictorial review focuses on what the radiologist should know about the most common MRI patterns of stroke mimics in the first hours after onset of symptoms. The issues linked to the accurate diagnosis of stroke mimics in the management of candidates for thrombolysis will be discussed.

[Grading of adults primitive glial neoplasms using arterial spin-labeled perfusion MR imaging]. / Évaluation du degré de malignité des tumeurs gliales primitives de l'adulte en IRM de perfusion par marquage des spins.

PURPOSE: We investigated the relationship between tumor blood-flow measurement based on perfusion-imaging by arterial spin-labeling (ASL) and histopathologic findings in adults' primitive glial tumours. PATIENTS AND METHODS: Thus, 40 primitive brain tumors (8 low-grade and 32 high-grade gliomas according to the Sainte-Anne classification) were imaged using pulsed (n=19) or continuous (n=21) ASL. Relative cerebral blood flow (rCBF=tumoral blood flow/normal cerebral blood flow) between high- and low-grade gliomas were compared. RESULTS: Using pulsed ASL, differences in mean rCBF were observed in high- and low-grade gliomas although no significant (respectively 1.95 and 1.5). Using continuous ASL, mean rCBF were significantly higher for high-grade than for low-grade gliomas (P<0.05). High-grade gliomas could be discriminated using a CBF threshold of 1.18, with a sensitivity of 88%, specificity of 60%, predictive positive value of 88%, and predictive negative value of 60%. CONCLUSION: ASL-based perfusion provides a quantitative, non-invasive alternative to dynamic susceptibility contrast perfusion MR methods for evaluating CBF. ASL is a suitable method for gliomas initial staging and could be useful to identify intermediate tumoral evolution.

[Diffusion-weighted MR imaging of the brain]. / IRM de diffusion et encéphale.

Imaging of water diffusion or diffusion-weighted MR imaging provides physiological information about brain diseases that cannot be obtained from conventional sequences. This technique is very sensitive for the detection of cerebral ischemia from arterial origin and can distinguish cerebral ischemia from other non-vascular brain pathologies in patients presenting with abrupt onset of focal neurological deficit. Diffusion-weighted imaging is used for the evaluation of non-vascular diseases as well. Combined with conventional sequences, it is helpful to differentiate brain abscesses from necrotic tumors. Quantitative diffusion-weighted imaging provides additional information in the characterization of tumors or inflammatory, degenerative and metabolic lesions. Finally, diffusion-weighted imaging data also has prognostic value.

Surgery for dysembryoplastic neuroepithelial tumors and gangliogliomas in eloquent areas. Functional results and seizure control.

INTRODUCTION: Dysembryoplastic neuroepithelial tumors and gangliogliomas are developmental glioneuronal tumors usually revealed by partial epilepsy. High epileptogenicity, childhood epilepsy onset, drug-resistance, temporal location, and seizure freedom after complete resection are common characteristics of both tumors. We report the specificity of surgical management, functional results and seizure outcome in cases of a tumor location in eloquent areas. METHODS: Among 150 patients (88 males, 3-55 years) operated on for refractory epilepsy due to a glioneuronal tumor (1990-2015), 30 (20%, dysembryoplastic neuroepithelial tumors=21; gangliogliomas=9) had a tumor located in an eloquent cortex (sensory-motor, insular or language areas). Surgery was performed after a preoperative work-up, including stereo-electroencephalography in 48 patients (26%) and functional MRI in 100 (67%). MRI-guided lesionectomy was mainly performed in extra-temporal location, whereas an additional corticectomy was performed in a temporal location. Tumor microsurgical resections were guided using neuronavigation and cortical/subcortical electrical stimulations. Multiple stereotactic thermocoagulations were performed in two insular tumors. RESULTS: New motor/language deficits related to eloquent areas occurred postoperatively in 6/30 patients (20%) without any major permanent disability. Minor sensorimotor (n=2) and moderate language disturbance (n=1) persisted in three of them. Postoperative seizure-free outcome (mean follow-up>5 years) was obtained in 81% of the entire series, but significantly decreased to 60% in eloquent areas. Incomplete tumor resection was the main cause of surgical failure. However, unfavorable seizure outcome was also observed despite complete tumor resection. Malignant transformation occurred in one ganglioglioma. CONCLUSION: Epilepsy surgery for benign glioneuronal tumors in eloquent areas provides acceptable results regarding the functional risks. Complete tumor resection is crucial for long-term favorable outcome.

Direct electrical bipolar electrostimulation for functional cortical and subcortical cerebral mapping in awake craniotomy. Practical considerations.

INTRODUCTION: The aim of brain glioma surgery is to maximize the quality of resection, while minimizing the risk of sequelae. Due to the frequent location of gliomas near or within eloquent areas, owing to their infiltrative feature, and because of major interindividual variability, the anatomofunctional organization and connectivity must be studied individually. Therefore, to optimize the benefit-to-risk ratio of surgery, intraoperative functional mapping is extensively used. MATERIAL AND METHODS: This article aims at describing the rationale, indications and practical aspects of intraoperative direct electrical bipolar electrostimulation for cortical and subcortical mapping under awake conditions using the asleep-awake asleep anaesthetic protocol in the setting of cerebral gliomas. We will address the operative approach, including patient positioning, functional mapping resection strategy, anaesthetic conditions, as well as tips and pitfalls. RESULTS: The intraoperative direct electrical bipolar electrostimulation enables: (i) to study the real-time individual cortical functional organization; (ii) to study the anatomofunctional subcortical connectivity along the resection; (iii) to tailor the resection according to individual corticosubcortical functional boundaries. This is an easy, accurate, reliable, well-tolerated and safe detection technique of both cortical and subcortical functionally essential structures during resection. It should be performed in the context of a standardized protocol involving members of both anaesthesiology and neurosurgery teams at neurosurgical centers specialized in surgical neuro-oncology. CONCLUSION: Intraoperative direct electrical bipolar electrostimulation for cortical and subcortical mapping under awake conditions is currently considered the "gold standard" clinical tool for brain mapping during cerebral resection in neuro-oncology.

Perioperative functional neuroimaging of gliomas in eloquent brain areas.

Surgical resection of gliomas involving eloquent brain areas must be maximal in order to improve patients' survival, and safe to prevent postoperative impairments. Therefore, the precise spatial relationship between the lesion and eloquent brain areas needs to be established. Functional magnetic resonance imaging and diffusion tensor imaging are robust methods with increasing indications in neurosurgery for past decade. The aim of this review article is not only to pinpoint the major limitations of these methods in order to avoid erroneous conclusions, but also to detail practical aspects associated with the main paradigms routinely used in functional magnetic resonance imaging, and to discuss recent validation of functional magnetic resonance imaging and diffusion tensor imaging results with direct electrical stimulation during awake surgery.

Do FLAIR vascular hyperintensities beyond the DWI lesion represent the ischemic penumbra?

BACKGROUND AND PURPOSE: In acute stroke with proximal artery occlusion, FLAIR vascular hyperintensities observed beyond the boundaries of the cortical lesion on DWI (newly defined "FLAIR vascular hyperintensity-DWI mismatch") may be a marker of tissue at risk of infarction. Our aim was to compare the occurrence of FLAIR vascular hyperintensity-DWI mismatch relative to that of perfusion-weighted imaging-DWI mismatch in patients with proximal MCA occlusion before IV thrombolysis. MATERIALS AND METHODS: In 141 consecutive patients with proximal MCA occlusion, 2 independent observers analyzed FLAIR images for the presence of FLAIR vascular hyperintensity-DWI mismatch before IV thrombolysis. PWI-DWI mismatch was defined as Volumehypoperfusion > 1.8 × VolumeDWI, with Volumehypoperfusion > 6 seconds on time to maximum value of the residue function maps in the 94 patients with available PWI. The presence of FLAIR vascular hyperintensity-DWI mismatch, PWI-DWI mismatch, and infarct growth on 24-hour follow-up DWI was compared. RESULTS: A FLAIR vascular hyperintensity-DWI mismatch was present in 102/141 (72%) patients, with an excellent interobserver reliability (κ = 0.91), and a PWI-DWI mismatch, in 61 of the 94 (65%) patients with available PWI. FLAIR vascular hyperintensity-DWI mismatch predicted PWI-DWI mismatch with a sensitivity of 92% (95% CI, 85%-99%) and a specificity of 64% (95% CI, 47%-80%). Patients with FLAIR vascular hyperintensity-DWI mismatch had smaller initial DWI lesion and larger infarct growth (P < .001) than patients without FLAIR vascular hyperintensity-DWI mismatch, even though their final infarcts remained smaller (P < .001). CONCLUSIONS: Albeit being moderately specific, probably due to inclusion of oligemic tissue, the FLAIR vascular hyperintensity-DWI mismatch identifies large PWI-DWI mismatch with high sensitivity.

Patient "candidate" for thrombolysis: MRI is essential.

Because of its excellent sensitivity and specificity to diagnose arterial ischemic stroke (AIS) in the acute phase, MRI answers the main questions to guide treatment in "candidates" for thrombolysis. It lasts less than ten minutes, can confirm the diagnosis of AIS and distinguish it from hematomas and other "stroke mimics". It can identify the ischemic penumbra (perfusion-diffusion mismatch), determine the site of occlusion and provide prognostic information to adapt treatment in some cases in which the indications are poorly defined. In light of the most recent scientific findings, MRI can guide the treatment turning it into the investigation of choice in "candidates" for thrombolysis.

Imaging of cervical artery dissection.

Cervical artery dissection (CAD) may affect the internal carotid and/or the vertebral arteries. CAD is the leading cause of ischemic stroke in patients younger than 45 years. Specific treatment (aspirin or anticoagulants) can be implemented once the diagnosis of CAD has been confirmed. This diagnosis is based on detection of a mural haematoma on ultrasound or on MRI. The diagnosis can be suspected on contrast-enhanced MRA (magnetic resonance angiography) or CT angiography, in case of long stenosis, sparing the internal carotid bulb, or suspended, at the junction of V2 and V3 segments of the vertebral artery, in patients with no signs of atheroma of the cervical arteries. MRI is recommended as the first line imaging screening tool, including a fat suppressed T1 weighted sequence, acquired in the axial or oblique plane at 1.5T, or 3D at 3T. Complete resolution of the lumen abnormality occurred in 80% of cases, and CAD recurrence is rare, encountered in less than 5% of cases. Interventional neuroradiology (angioplasty and/or stenting of the dissected vessel) may be envisaged in rare cases of haemodynamic effects with recurring clinical infarctions in the short-term.

Non-invasive diagnosis of intracranial aneurysms.

Patients need to be examined for intracranial aneurysms if they have had a subarachnoid hemorrhage. The preferred technique in this situation is CT angiography. Screening can be done for familial forms or for elastic tissue disorders, for which the first line investigation is magnetic resonance angiography. These non-invasive methods have now taken over from conventional angiography that was reserved for the pretreatment phase. A good technical knowledge of these imaging methods, their artifacts and misleading images enables reliable detection of intracranial aneurysms and for an accurate report to be returned to clinicians.

Tips and traps in brain MRI: applications to vascular disorders.

The French Society of Radiology's guide to good use of medical imaging examinations recommends MRI as the first-line examination for exploring cerebrovascular events or disorders. This paper will discuss the main traps in the images when stroke is suspected and provide the technical tips or knowledge necessary for an optimal radiological report.

Optimizing MR imaging detection of type 2 focal cortical dysplasia: best criteria for clinical practice.

BACKGROUND AND PURPOSE: Type 2 FCD is one of the main causes of drug-resistant partial epilepsy. Its detection by MR imaging has greatly improved surgical outcomes, but it often remains overlooked. Our objective was to determine the prevalence of typical MR imaging criteria for type 2 FCD, to provide a precise MR imaging pattern, and to optimize its detection. MATERIALS AND METHODS: We retrospectively reviewed 1.5T MR imaging of 71 consecutive patients with histologically proved type 2 FCD. The protocol included millimetric 3D T1-weighted, 2D coronal and axial T2-weighted, and 2D or 3D FLAIR images. Two experienced neuroradiologists looked for 6 criteria: cortex thickening, cortical and subcortical signal changes, blurring of the GWM interface, the "transmantle" sign, and gyral abnormalities. The frequency of each sign and their combination were assessed. We compared the delay between epilepsy onset and surgery, taking into account the time of type 2 FCD detection by MR imaging. RESULTS: Only 42 patients (59%) had positive MR imaging findings. In this group, a combination of at least 3 criteria was always found. Subcortical signal changes were constant. Three characteristic signs (cortical thickening, GWM blurring, and transmantle sign) were combined in 64% of patients, indicating that MR imaging can be highly suggestive. However, typical features of type 2 FCD were overlooked on initial imaging in 40% of patients, contributing to a delay in referral for surgical consideration (17 versus 11.5 years when initial MR imaging findings were positive). CONCLUSIONS: A combination of 3 major MR imaging signs allows type 2 FCD to be recognized in clinical practice, thereby enabling early identification of candidates for surgery.

FDG-PET improves surgical outcome in negative MRI Taylor-type focal cortical dysplasias.

OBJECTIVE: To determine the diagnostic accuracy and prognostic value of ¹8FDG-PET in a recent series of patients operated for intractable partial epilepsy associated with histologically proven Taylor-type focal cortical dysplasia (TTFCD) and negative MRI. METHODS: Of 23 consecutive patients (12 male, 7-38 years old) with negative 1.5-Tesla MRI, 10 exhibited subtle nonspecific abnormalities (e.g., unusual sulcus depth or gyral pattern) and the 13 others had strictly normal MRI. FDG-PET was analyzed both visually after coregistration on MRI and using SPM5 software. Metabolic data were compared with the epileptogenic zone (EZ) determined by stereo-EEG (SEEG) and surgical outcome. RESULTS: Visual PET analysis disclosed a focal or regional hypometabolism in 18 cases (78%) corresponding to a single gyrus (n = 9) or a larger cortical region (n = 9). PET/MRI coregistration detected a partially hypometabolic gyrus in 4 additional cases. SPM5 PET analysis (n = 18) was concordant with visual analysis in 13 cases. Location of PET abnormalities was extratemporal in all cases, involving eloquent cortex in 15 (65%). Correlations between SEEG, PET/MRI, and histologic findings (n = 20) demonstrated that single hypometabolic gyri (n = 11) corresponded to EZ and TTFCD, which was localized at the bottom of the sulcus. Larger hypometabolic areas (n = 9) also included the EZ and the dysplastic cortex but were more extensive. Following limited cortical resection (mean follow-up 4 years), seizure freedom without permanent motor deficit was obtained in 20/23 patients (87%). CONCLUSIONS: ¹8FDG-PET coregistered with MRI is highly sensitive to detect TTFCD and greatly improves diagnosis and surgical prognosis of patients with negative MRI.