[Infra tentorial tumors]. / Tumeurs de la fosse postérieure.

Infra tentorial tumors in adults are half as frequent as supra tentorial tumors. Extra-axial tumours are more frequent, mainly in the cerebellopontine angle cistern: vestibular schwannomas, meningiomas and epidermoid cysts. Tumors of the pons and cerebellum are fewer but medulloblastomas and hemangioblastomas are located primarily in the cerebellum: they are typical tumors of this area. Tumors of the IV ventricle are represented primarily by papilloma and ependymoma. The role of imaging is to ascertain the tumoral nature of the lesion and to determine its location.

[Pathology of the cerebellopontine angle]. / Pathologie de l'angle pontocérébelleux.

The pathology of the cistern of the cerebellopontine angle is primarily that of the nervous and vascular structures that it contains and of the meninges that line it. Knowledge of its anatomy makes it possible to understand and search for a rare pathology, the hemifacial spasm, due to a conflict between the facial nerve and the vertebral artery and the posterior inferior cerbellerar artery. However, the pathology of the cerebellopontine angle remains especially tumoral. Imaging should not only make the diagnosis but also make an exhaustive, pretherapy, and accurate assessment of the three main tumours found in this area: the vestibular schwannoma, the meningioma, and the epidermoid cyst.

Sensorimotor cortical activity in patients with complete spinal cord injury: a functional magnetic resonance imaging study.

Residual activation of the cortex was investigated in nine patients with complete spinal cord injury between T6 and L1 by functional magnetic resonance imaging (fMRI). Brain activations were recorded under four conditions: (1) a patient attempting to move his toes with flexion-extension, (2) a patient imagining the same movement, (3) passive proprio-somesthesic stimulation of the big toes without visual control, and (4) passive proprio-somesthesic stimulation of the big toes with visual control by the patient. Passive proprio-somesthesic stimulation of the toes generated activation posterior to the central sulcus in the three patients who also showed a somesthesic evoked potential response to somesthesic stimulation. When performed under visual control, activations were observed in two more patients. In all patients, activations were found in the cortical areas involved in motor control (i.e., primary sensorimotor cortex, premotor regions and supplementary motor area [SMA]) during attempts to move or mental imagery of these tasks. It is concluded that even several years after injury with some local cortical reorganization, activation of lower limb cortical networks can be generated either by the attempt to move, the mental evocation of the action, or the visual feedback of a passive proprio-somesthesic stimulation.

MR of cerebral malaria.

In three cases of cerebral malaria, MR imaging disclosed either cortical infarcts (one case) or hyperintense areas of white matter (two cases) on T2-weighted and fluid-attenuated inversion-recovery sequences. These white matter abnormalities were, in one case, sharply limited, symmetrical, hyperintense, and unenhanced; in the other case, they were diffuse, hyperintense, and had a more limited focus. The diffuse hyperintensity was probably due to edema, whereas focal lesions were probably associated with gliosis.

[Simultaneous hepatic cholangiocarcinoma and bone fibrosarcoma 45 years after ingestion of Thorotrast]. / Cholangiocarcinome hépatique et fibrosarcome osseux synchrones 45 ans après injection de Thorotrast.

This case of a 63 year old man reports the simultaneous development of hepatic cholangiocarcinoma and fibrosarcoma of the sacrum 45 years after the systemic injection of Thorotrast. The characteristic radiologic aspect was an important criteria for diagnosis. Biopsies have confirmed the histology of both tumors. We describe the way to thorotrastosis diagnosis and characteristic malignant tumors, especially cholangiocarcinoma, induced by Thorotrast.

[Toxic aluminum encephalopathy. Predominant involvement of the limbic system on MRI]. / Encéphalopathie toxique à l'aluminium. Atteinte prédominante du système limbique en IRM.

Two patients underwent acoustic schwannoma surgery by transmastoid approach. Petrous bone defect was filled in with aluminium-containing bone cement (Ionocem). A pseudomeningocele by CSF accumulation in subcutaneous temporoparietal area appeared after the procedure and, in subsequent weeks, encephalopathy with confusion and seizures. MRI showed cerebral involvement with herpes-like disposition. Temporal stereotactic biopsy in a case did not confirm viral encephalitis but disclosed cellular accumulation of lipofucsin and particles highly suggestive of aluminum-inclusions. Aluminium's levels in blood and CSF of both patients were very high and confirm the brain's toxic involvement. Aluminium's toxicity would be advocated in patients with neurologic disorders who have undergone maxillofacial or skull bone-cementoplasty by an aluminum-containing biomaterial, if this cement is in contact with CSF.

[Imaging of encephalic parasitic diseases]. / Imagerie des parasitoses encéphaliques.

We review the main cerebral parasitic diseases, with emphasis on the most frequently encountered in Europe.

[MRI aspects of progressive multifocal leukoencephalopathy]. / Aspects IRM de la leucoencéphalopathie multifocale progressive.

Progressive Multifocal Leukoencephalopathy is a demyelinating disease. MRI shows high signal intensity areas on T2w sequence and low intensity aeras on T1w sequence, without enhancement after intravenous contrast injection. The involvement of arcuate fiber (U fibers) creates a sharp border with the cortex. There is no mass effect. Involvement of parieto-occipital areas is frequent. The lesions may be uni or bilateral, single or multiple; bilateral lesions are asymmetric. This typical appearance on MR images occurs in 90% of the patients with PML. Some atypical patterns may occur: focal hemorrhage, atrophy, faint peripheral enhancement and involvement of deep gray matter (basal ganglia). In most cases, the clinical and MR features provide the diagnosis. The main differential diagnosis, in MRI, is HIV-leukoencephalitis, but lesions are diffuse, less intense on T2w sequence and not visible on T1, without involvement of the arcuate fibers. Stereotactic biopsy should be performed only for atypical lesions, particularly in case of predominant involvement of deep gray structures.

[The foramen rotundum. Anatomy and radiological explorations. Pathology]. / Le foramen rond. Anatomie et exploration radilogiques. Patholgie.

The foramen rotundum is a small canal deeply situated in the base of the skull which represents the way of exit of the maxillary nerve, second branch of the trigeminal nerve. Its precise individualization and analyse is difficult and necessitates a precise and adapted technique as well as a precise knowledge of its anatomical relationships. Its represents a frontier area between the endo- and exocranial spaces. Its involvement which is preferentially related with tumoral pathologies (and particularly with retrograde perineural invasion) profoundly modifies the prognosis of the disease and so should allow soon a multidisciplinary therapeutic discussion.

[Magnetic resonance imaging and meningiomas of the posterior cerebral fossa. 31 cases]. / Imagerie par résonance magnétique et méningiomes de la fosse cérébrale postérieure. 31 cas.

To assess the value of MRI for meningioma of the posterior cerebral fossa, in correlation with surgical and pathological findings, we retrospectively reviewed 31 cases. The patients (24 females and 6 males ranging in age from 25 to 79 years) were preoperatively studies on a 1,5 T MR imager (GEMS Signa) between july 1989 and november 1993. The protocol included: 1. MR scan with axial sections in T2-weighted spin-echo sequence (3 mm thickness), T1-weighted spin-echo sequence before and after gadolinium injection (3-5 mm thickness), coronal and sagittal T1-weighted sections performed after injection. 2. Surgery reports. 3. Histopathological reports; the predominant histological subtype of each tumor was graded according to the classification scheme of Russel and Rubinstein. We focused on five items: 1. The site of the dural attachment of the meningioma. 2. Tumoral extensions (to the tentorium, to the jugular foramen, to the internal auditory canal). 3. The meningioma signal in T1- and T2-weighted sequence using the same visual scoring system for grading signal intensities as Elster and al. 4. Secondary features (necrosis, cysts, calcifications) within the tumor. 5. Interface between meningioma and encephalic structures. Meningiomas arose from the posterior surface of the petrous bone in 74% of the cases and from the clivus in 9.6%. Meningiomas were bulky at the time of diagnosis as since tumoral arrow overtook 2 cm in 64.5% of the cases. Surgical approach was guided by an anatomo-radiologic classification based on the exact site of tumoral dural attachment. This determination relied on: 1. Osseous reaction noted in 58% of the cases (enostosic spur in 19%, localized osseous thickening in 16%). 2. The trigeminal nerve displacement by the tumor; in case of clival meningioma extended to the petrous apex, this nerve is displaced outside; otherwise, meningioma of the petrous bone extended to the clivus displaced the trigeminal nerve inside. 3. Radiate structure within tumor converging to vascular basal pole of the meningioma noted in 42% of the cases. Tentorial involvement remained a difficult diagnosis on MR images. It was affirmed when the tumor extended on the opposing surface of the tentorium and when focal hypersignal existed through the usual tentorial hyposignal on T2-weighted images and T1-weighted images after gadolinium. On the other hand, tentorial linear dural enhancement adjacent to the tumor was not a reliable sign (error in 15.8% of the predicted cases). The meningothelial (syncitial) type was noted in 67.7% of the cases. (ABSTRACT TRUNCATED AT 450 WORDS)

[Clinical application of functional MRI: a strategic tool for neurosurgery]. / Application clinique de l'IRM fonctionnelle: aide à la stratégie neurochirurgicale.

The purpose was to incorporate preoperative functional imaging data into anatomic data of operative microscope for neurosurgical procedures of patients suffering from lesions contiguous to eloquent brain areas. The day before surgery, patients bearing scalp markers underwent fMRI, just before anatomical contrast-enhanced MR images. FMRI data analysis were realised using a t test (p<0.0001). The resulting functional-anatomical images were downloaded onto a surgical neuronavigation computer in order to outline tumoral target and functional areas. At surgery, cortical stimulation has been used to confirm functional data. Functional image-guided surgery of lesions abutting functional cortex can be safely performed.

Functional MR imaging and traumatic paraplegia: preliminary report.

PURPOSE: To evaluate residual activity in the sensorimotor cortex of the lower limbs in paraplegia. METHODS: 5 patients suffering from a complete paralysis after traumatic medullar lesion (ASIA=A). Clinical evaluation of motility and sensitivity. 1. Control functional MR study of the sensorimotor cortex during simultaneous movements of hands, imaginary motor task and passive hands stimulation. 2. Concerning the lower limbs, 3 fMRI conditions: 1-patient attempts to move his toes with flexion-extension, 2-mental imagery task of the same movement, 3-peripheral passive proprio-somesthesic stimulation (squeezing) of the big toes. RESULTS: Activations were observed in the primary sensorimotor cortex (M1), premotor regions and in the supplementary motor area (SMA) during movement and mental imaginary tasks in the control study and during attempt to move and mental imaginary tasks in the study concerning the lower limbs. Passive somesthesic stimulation generated activation posterior to the central sulcus for 2 patients. CONCLUSION: Activations in the sensorimotor cortex of the lower limbs can be generated either by attempting to move or mental evocation. In spite of a clinical evaluation of complete paraplegia, fMRI can show a persistence of sensitive anatomic conduction, confirmed by Somesthesic Evoked Potentials.

[Epithelioid sarcoma. Diagnostic and therapeutic aspects apropos of a coccygeal localization]. / Sarcome épithélioïde. Aspects diagnostiques et thérapeutiques à propos d'une localisation coccygienne.

A rare case of epithelioid sarcoma of the coccyx is described. A 23-year-old man had coccidynia for 2 years, becoming permanent. The patient underwent an "en bloc" excision including a resection of the extremity of the coccyx. Postoperatively, six cycles of a chemotherapy combining ifosfamide and adriamycine were alternated with a 60 Gy external beam radiotherapy. The patient remains free of disease 9 months after the operation. We review the clinical characteristics and treatment of epithelioid sarcoma.

[Imaging of postoperative lumbar spine]. / Imagerie du rachis lombaire opéré

Complications following lumbar spine surgery are reported to occur in 15 to 30% of cases. Acute postsurgical complications (hematoma, infection.) require urgent imaging. Imaging of recurrent pain following lumbar surgery, often with a clinical presentation that is poorly specific in nature, is sometimes difficult. Selection of the initial imaging technique must simplify the diagnostic work-up. Because of its high contrast resolution, pre- and postcontrast MRI is the most effective imaging technique. Noncontrast CT may be added to facilitate detection of bony abnormalities. Diskography with post-diskogram CT can be added as well in patients with discordant results at clinical and imaging work up. The main causes of failed back syndrome are recurrent disk herniation (usually easily diagnosed), postsurgical granulation tissue/epidural fibrosis (diagnosed based on imaging) and central or lateral bony spinal stenosis. Spondylodiskitis, arachnoiditis and pseudomeningocele are other less frequent etiologies.

[Hypersignal of the intervertebral disks in T1-weighted spin-echo MRI sequences]. / Disques intervertébraux en hypersignal sur les séquences d'IRM en écho de spin pondéré T1.

In magnetic resonance imaging, when there is calcification of the intervertebral disk, signals usually become weaker in all the sequences. Exceptionally, a spontaneous hypersignal is obtained in T1 weighted spin-echo sequences. We report 4 cases of spontaneous hypersignals from disks in T1 weighted spin-echo sequences. In 3 cases, calcifications were visualized with conventional radiology or computed tomography. In 1 case, there was no calcification of the disk, but its density, compared with adjacent disks, was 20 HU greater, suggesting inframacroscopic calcification.

[Spinal osteoid osteoma, neuralgia and MRI]. / Ostéome ostéoïde rachidien, radiculalgie et IRM.

Computed Tomography (CT) is the most valuable imaging modality for the diagnosis of osteoid osteoma. Magnetic Resonance Imaging (MRI) is less performant than CT. However, in case of neuralgia a disk disease is searched for and MRI is often performed at first. The authors report 2 cases of MRI diagnosis of osteoid osteomas histologically proved. The presence of bone marrow and soft tissues changes consistent with inflammation adjacent to the nidus is the main sign. Inflammatory changes are characterized by low signal on T1-weighted sequence, high signal on T2 and enhancement after gadolinium IV administration. These changes are not specific. But in these 2 cases, an osseous abnormality was detected and the nidus was suspected even if MRI was less conspicuous than CT. In case of children or young adults with radiculalgia and normal disk, inflammatory localized changes in MRI must be suspicious of the diagnosis of osteoid osteoma.

[Agenesis of the internal carotid artery: two cases report]. / Agénésie de l'artère carotide interne: à propos de deux cas.

The authors report two cases of agenesis of the internal carotid artery evaluated with MR angiography allows the diagnosis of the internal carotid artery agenesis and appreciates both the supply post.

[Circumscribed myositis ossificans: bone changes detected by MRI]. / Myosite ossifiante circonscrite: remaniements osseux décelés en IRM.

The authors report a case of ossificans myositis, in which MRI showed inflammatory changes of the adjacent bone. T1 weighted fat saturation sequence with gadolinium injection showed enhancement of medullary and cortical bone. This potentially mistaking pattern must be known, to avoid misdiagnosing with malignant osseous tumor, specially before achievement of the characteristic pattern of zonal maturation and its calcified rim.

[Exposure and good practice in helical computed tomography]. / Irradiation et bonnes pratiques en tomodensitométrie hélicoïdale.

Helical CT is the imaging modality that delivers the highest exposure to patients. For each acquisition, the average radiation dose is between 20 and 30 mGy. This dose can potentially be reduced by decreasing the intensity or voltage and by increasing the pitch. Helical data can be reformatted to obtain images with smaller increment or multiplanar reconstructions, hence reducing the need for additional acquisitions. Hardware and software devices designed for dose reduction must be systematically used. Operators of CT units should be aware of the radiation dose delivered with helical CT and must carefully assess the need of each additional acquisition. Obsolete protocols such as angulation of the gantry for lumbar CT, which increases patient exposure, should no longer be used. Rational use of helical CT decreases radiation exposure and is faster, whereas improper use increases radiation exposure without added benefit.

[A rare case of chondroid chordoma of the cervical spine]. / Un cas rare de chordome chondroïde du rachis cervical.

Chordoma is a rare tumor in spine. Authors report the case of a 49 years old woman suffering from C5 left neuralgia. Plain films showed an enlargement of C4-C5 left foramina. CT scan permitted to see a lobulated tumor with low density just a few enhancement into septa. MRI showed the tumor with low signal on T1wi, high signal on T2wi and slight enhancement after Gadolinium administration. The extension in the vertebral body is very limited. Differential diagnosis are chondroma or chondrosarcoma and epidermoid cyst. Histology with evidence of a chondroid matrix explain the CT and MR appearance. In this localisation, there is no case reported in the litterature. This is an outstanding case because its extra-osseous localization with a lack of contrast enhancement after injection and its unusual histologic pattern.