Tips and traps in neurological imaging: imaging the perimedullary spaces.

The spinal canal is frequently a source of difficulties, traps and diagnostic errors. Pitfalls related to artifacts are resolved by using appropriate sequences. Good knowledge of the appearance of certain particular anatomical structures (the cauda equina roots, the radicular veins of the lumbar spine and conus medullaris, the dorsal root ganglion) and of frequent variants (fibrolipoma of the filum terminale, common root sheaths, root cysts) will avoid a good many errors. Dilatation of epidural veins in intracranial hypotension can simulate the contrast enhancement of a tumour. An increase in epidural fat can induce pathogenic stenosis of the dural sheath.

[Imaging spinal cord cystic lesions in adults]. / Imagerie des lésions kystiques du canal rachidien chez l'adulte.

Intrarachidian cystic lesions are frequent, with highly varied causes. They can be classified according to their location into intramedullary cystic lesions and extramedullary cystic lesions. In these two categories, they can then be regrouped according to the tissue from which they develop. MRI is the first-choice examination for the study of the intracanal contents and the differential diagnosis between the various lesions.

Accuracy of delayed post-contrast FLAIR MR imaging for the diagnosis of leptomeningeal infectious or tumoral diseases.

AIMS: To compare unenhanced, gadolinium enhanced, delayed gadolinium enhanced FLAIR images, gadolinium enhanced and delayed gadolinium enhanced T1 images in different types of leptomeningeal diseases, and to determine the most accurate MRI sequence for the diagnosis of leptomeningeal disease. MATERIAL: and methods: Ten patients (6 men, 4 women, age: 52,7+/-16,4) clinically suspected of cerebral leptomeningeal infectious or tumoral disease underwent brain MR examination: Axial FLAIR and T1 SE images were acquired before, immediately after administration of gadobenate dimeglumine (0.1 mmol per kilogram of body weight) (early enhancement), and 20 minutes after injection of contrast media (delayed enhancement). Images were analysed to determine the more appropriate technique for the diagnosis of leptomeningeal disease. RESULTS: Early enhanced FLAIR and delayed enhanced T1 were always more or equally accurate for the diagnosis of leptomeningeal diasease, as compared to, respectively, unenhanced FLAIR and early enhanced T1 images Delayed enhanced FLAIR was always more accurate for the diagnosis of leptomeningeal disease as compared to early enhanced FLAIR images. Delayed enhanced FLAIR was in most of the cases more accurate for the diagnosis of leptomeningeal disease as compared to delayed enhanced T1 images. CONCLUSION: Delayed enhanced FLAIR MR sequence seems to improve the diagnosis of leptomeningeal infectious or tumoral diseases as compared to other MR sequences.

[Normal and abnormal meningeal enhancement: MRI features]. / Les prises de contraste méningées normales et pathologiques en IRM.

The authors describe normal imaging of the meninges and meningeal spaces and MR (magnetic resonance) imaging findings in tumoral and nontumoral diseases. Dural or/and pial enhancement may be related to tumoral, infectious or granulomatous diseases.

[Imaging in acute toxic encephalopathy]. / Imagerie des encephalopathies toxiques aigues.

Neuroimaging, particularly MR imaging, plays a major role for the diagnosis of many acute toxic encephalopathies. Toxic disorders are related to drugs (immunosuppressive agents, chemotherapeutic agents, anti-epileptic drugs, heroin...), to metals (lead, manganese, mercury...), and to industrial and environmental chemicals (solvent, carbon monoxide...). MR imaging with diffusion and perfusion imaging provides information regarding brain lesions induced by the toxic agents (vasogenic edema, cytotoxic edema, infarction, hemorrhage, demyelination...).

[Spinal extradural meningiomas: MRI findings in two cases]. / LES MENINGIOMES RACHIDIENS EXTRADURAUX: DONNEES IRM A PROPOS DE DEUX OBSERVATIONS.

Spinal extradural meningiomas are rare and may be easily confused with malignant neoplasms. We report two unusual cases of epidural spinal meningioma one within the left C6-C7 foramen and the other within the left posterolateral epidural space at the T3-T4 level. Low signal intensity of the tumor on T2-wi, thickening and enhancement of the dura with only the possibility of bone erosion are the most characteristic MR findings.

[Brain MR imaging of chronic alcoholism]. / Imagerie par résonance magnétique (IRM) des complications encéphaliques de l'alcoolisme.

Brain complications from chronic alcoholism (Wernicke encephalopathy, central pontine myelinolysis, Marchiafava-Bignami disease, Korsakoff's syndrome, hepatic encephalopathy, cerebellar atrophy, hemorrhagic and ischemic brain lesions) may be diagnosed by MR imaging.

[Siderosis of the brain and spinal cord. Report of two cases]. / Sidérose cérébrale et médullaire. A propos de deux observations.

Two cases of superficial siderosis of the brain and spinal cord with cochleovestibular and cerebellar symptoms are diagnosed on brain and spinal MRI scans. Low signal intensity lines are noted on the surface of the brainstem, cerebellum, spinal cord and within the interhemispheric and sylvian fissures. In one case, no brain or vascular malformation is identified; in the second case, two cavernous angiomas are noted on the MRI study. 3D CISS may visualize thickening of the cochleovestibular nerve.

[Epidermoid cyst of the fourth ventricle: four case reports]. / Les kystes épidermoïdes du quatrième ventricule: à propos de quatre cas.

Patients with epidermoid cyst of the fourth ventricle usually present with headaches and/or disequilibrium. These cysts are characterized by a focal lesion that is nearly isodense to CSF at CT and nearly isointense to CSF on T1W and T2W MR images. MRI using FLAIR and diffusion weighted images as well as 3D CISS acquisitions is useful to better characterize the lesions and their relation with the vermis, foramen magnum and CP angle cisterns. DWI images are useful for postsurgical evaluation of residual tumor. Extension of the cyst into the CP angle cisterns usually precludes complete surgical resection.

[Value of MRI findings in Gayet-Wernicke encephalopathy]. / Apport de l'IRM dans l'exploration de l'encéphalopathie de Gayet-Wernicke.

Wernicke encephalopathy (Wernicke-Korsakoff encephalopathy) is related to thiamine deficiency. We report the MRI findings in four patients with visualization of bilateral and symmetrical hyperintense foci on T2W and FLAIR images involving the periaqueductal gray matter, the mamillary bodies and around the third ventricle. Diffusion weighted images obtained in two patients demonstrated mild hypersignal in the same areas. Contrast enhancement within the mamillary bodies was noted in one patient. Follow-up MRI obtained in three patients showed rapid regression of signal abnormalities without correlation with good clinical outcome.

[Intracerebral radiation-induced cavernous angiomas]. / Les angiomes caverneux cérébraux induits par la radiothérapie.

We present four cases of cerebral cavernous angioma that developed after radiatherapy for brain tumor in three cases and for cavernous angioma in one case. The time interval between irradiation and the detection of the cavernous angioma varied from three to nine years and the doses from 24 to 60 Grays. Brain hemorrhage appeared in two cases. Explanation for the formation of cavernous malformations is unclear but is probably related to proliferation and dilatation of the vascular endothelium with formation of capillary telangiectasis with evolution to cavernous angiomas. The pediatric brain appears particularly vulnerable to radiation injury. The risk of hemorrhage appears higher than with spontaneous cavernous malformations.

[Aspects of FLAIR sequences, 3D-CISS and diffusion-weight MR imaging of intracranial epidermoid cysts]. / Aspects en séquences FLAIR, CISS-3D et en imagerie de diffusion des kystes épidermoïdes intracrâniens.

We propose to assess the usefulness of diffusion-weighted MR Imaging (DWI), fluid-attenuated inversion recovery (FLAIR) and constructive interference in steady state (CISS) sequences in depicting epidermoid cysts (EC). FLAIR, CISS and DWI were obtained in 7 patients among 22. All patients were studied with T1 and T2 sequences. On Spin Echo images, EC demonstrate signal similar to LCS, which may lead to difficult differentiation between EC and arachnoid cyst (AC), specially for inexperienced radiologists. EC appear with a heterogeneous signal on T1 images (32%), irregular limits (91%) and with extension through foramen of Pacchioni in 18% of cases. On FLAIR sequence, the tumors were heterogeneous, different from void signal of CSF in 86% of cases. On CISS sequence, the tumors appear heterogeneous, hyperintense but less than LCS and with irregular limits in all cases. Some more, CISS images allowed to appreciate exact tumor extension and their relations with nerves and vessels. On DWI images, signal is hyperintense in all cases. Our study exhibited the great usefulness of DWI, CISS and FLAIR sequences in diagnosis of EC and in differentiating EC from AC.

[Contribution of 3D CISS MRI for pre- and post-therapeutic monitoring of obstructive hydrocephalus]. / Intérêt des séquences IRM "CISS 3D" dans le bilan pré- et post-thérapeutique des hydrocéphalies non communicantes.

This report describes the use of the recent three-dimensional Fourier transform constructing imaging in the steady state (CISS) MR sequence in the management of obstructive hydrocephalus. It is a gradient-echo imaging technique with high resolution which remains sensitive to flow. It enables locating the obstruction and determining the upstream impact. It provides anatomical information about third ventricle (V3) morphology and relationships useful before ventriculostomy. Twenty patients with obstructive hydrocephalus at the level of cerebral aqueduct or posterior V3 underwent sagittal 3DFT-CISS acquisition, supplemented by frontal, axial and coronal reformations in the cerebral aqueduct axis. 9 patients were examined after ventriculostomy with the same protocol. CISS-3DFT allows good visualization of the cerebral aqueduct and diagnosis of the underlying cause of obstruction (malformation, tumor), sometimes better than classical sequences. In case of complete obstruction, the flow-related signal void is usually absent in the cerebral aqueduct or V3. The position of V3 floor and its relationship with the tip of basilar artery are well analyzed. The dilatation of the anterior V3 recesses is a better sign of activity of hydrocephalus - and then of therapeutical indication - than classical transependymal resorption signs which are not always present in chronic longstanding adult hydrocephalus. Of the 9 ventriculostomy patients seven had linear flow-related signal void through V3 floor, from anterior V3 to basal cisterns on the postoperative MR study. This flow void confirms patent ventriculostomy.

MRI in multiple sclerosis of the spinal cord: evaluation of fast short-tan inversion-recovery and spin-echo sequences.

We compared the sensitivity of T2-weighted spin-echo (FSE) and fast short-tau inversion-recovery (fSTIR) sequences in detection of multiple sclerosis of the spinal cord in 100 consecutive patients with clinically confirmed multiple sclerosis (MS); 86 patients underwent also brain MRI. In all, 310 focal lesions were detected on fSTIR and 212 on T2-weighted FSE, spinal cord lesions were seen better on fSTIR images, with a higher contrast between the lesion and the normal spinal cord. In 24 patients in whom cord plaques were shown with both sequences, the cranial study was normal or inconclusive. Assessment of spinal plaques can be particularly important when MRI of the brain is inconclusive, and in there situations fSTIR can be helpful.