1H MRS spectroscopy evidence of cerebellar high lactate in mitochondrial respiratory chain deficiency.

Cerebellar ataxia is known to occasionally occur in the course of mitochondrial disorders. We report on MR spectroscopy (1H MRS) evidence of elevated brain lactate in the cerebellar area of 11 patients with cerebellar ataxia ascribed to mitochondrial respiratory chain deficiency (RCD). 1H MRS spectroscopy evidence of lactate peak was found in the cerebellum of 9/11 cases, while no lactate was detected in the putamen in 8/11. We suggest using 1H MRS in cerebellar atrophy in the diagnosis of mitochondrial RCD.

[Imaging of intracranial metastases in adults]. / Imagerie des métastases intracrâniennes chez l'adulte.

Intracranial metastases account for up to 35% of intracranial tumors in adult. They can involve any part of the central nervous system: brain, meninges and cranial nerves. Any systemic tumor can metastasize to the brain; the most common primaries include lung, breast and melanoma. Imaging plays a major role in the evaluation and management of patients with metastatic brain tumors. This article discusses optimal CT and MR imaging protocols and describes imaging features and distinguishing characteristics of cerebral and meningeal metastases.

[Cervical arteries dissection: diagnostic Color Doppler US criteria at the acute phase]. / Critères diagnostiques en échographie-Doppler des dissections artérielles cervicales à la phase aiguë.

PURPOSE: To estimate the value of duplex color-coded ultrasonography in the initial diagnosis of acute cervical artery dissection. MATERIAL AND METHOD: Retrospective study of 31 patients, mean age 45, sex ratio=1, referred for clinical suspicion of cervical artery dissection, confirmed by MRI. 46 dissected arteries were imaged. Ten patients presented multiple dissections. The evaluated sonographic diagnostic criteria were the direct signs of intra-mural hematoma: localized increased diameter of the artery, narrowed lumen, hypo and/or isoechoic intra-mural hematoma, intimal flap. The associated criteria studied were: the location of intra-mural hematoma and in case of an occlusion, the dissection of an other artery. RESULTS: We analyzed separately the arterial segments visualized in B-mode ultrasound (supra-bulbar internal carotid artery, vertebral artery from V0 to V3) and the arterial segments evaluated only by pulsed Doppler (intrapetrosal carotid artery, V3-V4 of the vertebral artery). With the above criteria, on arterial segments visualized in B-mode ultrasound, the diagnosis of dissection was done in 83% of cases during the initial examination but in only 30% of the arterial segments non visualized on ultrasonography. CONCLUSION: The direct signs of intra-mural hematoma on internal carotid and vertebral segments imaged by B-mode ultrasonography have a good sensitivity. Because results were compared to MRI, the specificity could not be assessed. In case of occlusion of an artery, multiple dissections are a strong argument for the diagnosis.

[MRI for oligodendrogliomas]. / IRM des oligodendrogliomes.

MRI has dramatically improved the management of cerebral tumors and consequently oligodendrogliomas. T1 and T2-weighted images and gadolinium enhancement are very useful for tumor detection and characterization. Tumor enhancement is of a great prognostic value because it is highly predictive of high-grade oligodendroglioma. Three-dimensional MR images provide, with high precision, the anatomical location and the relationships with functional structures (motor and language areas). The recent technical progress in MRI and the use of diffusion images in the screening of tumors lead to a better definition of the lesion. Comparative analysis of MRI images is helpful to detect eventual relapse and adverse effects of treatment.

[MRI of acute ischemic stroke]. / Imagerie de l'ischémie cérébrale dans les premières heures: IRM.

The advent of new MR techniques such as perfusion and diffusion weighted imaging has revolutionized diagnostic imaging in stroke. In some institutions, MRI is used as the sole screening imaging technique for acute stroke patients. In this document, the authors will review the MR pattern of acute ischemic arterial stroke, highlight the usefulness of MRI for the identification of acute hematomas and stroke like episodes, present the potential use of MRI in the management of acute stroke patients, especially when thrombolysis is contemplated, and discuss the role of MRI for imaging transient ischemic attack.

[Abnormalities of the basal ganglia and thalami in adults]. / Atteintes bilatérales des noyaux gris chez l'adulte.

Several diseases may cause non-specific MR signal abnormalities of the bilateral basal ganglia and thalami. As such, diagnosis of the underlying etiology may be difficult to achieve at imaging. In this review, we will present interpretative guidelines based on clinical data (mode of presentation, previous history, clinical symptoms, and evolution) and imaging data (type of signal abnormalities, location of lesions, and associated abnormalities). The main categories of diseases causing MR signal abnormalities of the bilateral basal ganglia and thalami in adults are reviewed: toxic, metabolic, vascular, tumoral, infectious and inflammatory diseases.

[Normal results]. / Les résultats normaux.

THE TECHNIQUE: Today, magnetic resonance imaging (MRI) is the exploration of choice for a number of central nervous system disorders. This technique, which does not use ionising rays, examines the encephalus in all its dimensions. Various sequences are used to study the cerebral parenchyma: specific sequences in T1, with or without injection of a contrast product, specific sequence in T2, and FLAIR sequence. THE RESULTS OBTAINED: The diffusion and perfusion imaging respectively reveal the movement of the water molecules and the cerebral microcirculation. Visualisation of the arteries and veins is non-invasive with magnetic resonance angiographical techniques. Study of the chemical composition of tissues (magnetic resonance spectroscopy) and of cerebral activation (functional activation imaging) will not be addressed.

[Tumor pathology]. / Pathologie tumorale.

THE MRI DIAGNOSTIC SUPPORT: Magnetic resonance imaging is an efficient technique for revealing an intercranial tumor, and specifying its topography and loco-regional impact. A macroscopical approach is possible with MRI, since it distinguishes the components: tumoral tissue, cyst, necrosis and hemorrhage. DEPENDING ON THE TUMOR: Assessment of the tumoral limits is easy for extra-axial tumors. However, it is imprecise or even impossible for infiltrating intra-axial tumors. MRI specificity is low, however some lesions such as meningiomas, glioblastomas, arachnoid cysts and neurinomas are evocative.

[Vascular pathology]. / Pathologie vasculaire.

IN ARTERIAL ISCHEMIC PATHOLOGY: Magnetic resonance imaging is increasingly proposed for any suspicion of cerebral vascular accident. Because of its diffusion sequences, it permits the rapid diagnosis and screening of ischemic lesions and provides prognostic information. FOR OTHER CEREBRAL VASCULAR DISORDERS: Intra-parenchymatous and sub-arachnoid hemorrhages are easily revealed by MRI. Today, MRI is the most effective examination for the diagnosis of venous thrombosis and of its impact on the parenchyma.

[Traumatic, infectious or degenerative pathology]. / Pathologie traumatique, infectieuse ou dégénérative.

CRANIO-ENCEPHALIC TRAUMAS: Scanography remains the examination of choice. However, MRI can be useful in diagnosis of diffuse axional lesions, not clearly visualized with scanography, and for screening the subsequent lesions. INFECTIOUS OR INFLAMMATORY LESIONS: Some are very evocative with MRI: cerebral abscesses, notably herpetic encephalitis and Creutzfeldt-Jacob's disease. If multiple sclerosis is suspected, MRI is considered as the principle para-clinical examination able to confirm the diagnosis with the first episode. It also supplies data for the diagnosis of metabolic, toxic and degenerative diseases.

[Transcranial Doppler imaging: state of the art]. / Echo-Doppler transcrânien: Mise au point.

Initially introduced in the early 1980's, transcranial Doppler followed by transcranial Doppler sonography were used in neurosurgical units for management and follow-up of intracranial vasospasm in patients with subarachnoid hemorrhage. This imaging technique, more sensitive and less invasive than catheter angiography, also proved to be of value for diagnosis of intracranial atherosclerosis, management of patients with head trauma, and evaluation of collateral flow through the circle of Willis. Doppler US would also allow prediction of the risk of symptomatic embolic events through monitoring of HITS. Evaluation of the middle cerebral arteries during carotid occlusion testing is useful for evaluating the need for particular revascularization techniques. Finally, Doppler imaging is useful to assess patients with possible brain death. A recent advance in Doppler imaging is the ability to provide a three-dimensional projection (3D Doppler) of the intracranial arteries enabling improved detection and evaluation of stenoses involving the circle of Willis and improved characterization of intracranial aneurysms. These new applications benefit from the use of US contrast agents and harmonic US imaging.

[MRI aspects of central nervous system sarcoidosis]. / Aspects en IRM de la sarcoïdose du système nerveux central.

Sarcoidosis is a multisystemic disease of unknown origin characterized pathologically by the presence of noncaseating epithelioid granulomas. Symptomatic involvement of the CNS may develop in a patient with known sarcoidosis or it may be the initial manifestation. Intracranial sarcoidosis may include meningeal disease, cranial neuropathy, hypothalamic and pituitary dysfunction and both intraaxial and extraaxial mass. The MRI features are variable and non specific, so differentiation from other lesions (multiple sclerosis, tumour, meningitis, vasculitis) may be difficult, especially in the absence of extracranial disease. Patients with symptoms usually have corresponding CNS lesions at MR imaging, except for cranial nerves involvement. Under therapy, resolution of lesions at MR imaging lags behind resolution of clinical symptoms. MRI may contribute to confirm a clinically suspected diagnosis or detect subclinical involvement. MRI is also very helpful for follow-up under therapy.