Jacqueline Delavelle

Non-invasive epileptic focus localization using EEG-triggered functional MRI and electromagnetic tomography

We present a new approach for non-invasive localization of focal epileptogenic discharges in patients considered for surgical treatment. EEG-triggered functional MR imaging (fMRI) and 3D EEG source localization were combined to map the primary electrical source with high spatial resolution. The method is illustrated by the case of a patient with medically intractable frontal lobe epilepsy. EEG obtained in the MRI system allowed triggering of the fMRI acquisition by the patients habitual epileptogenic discharges. fMRI revealed multiple areas of signal enhancement. Three-dimensional EEG source localization identified the same active areas and provided evidence of onset in the left frontal lobe. Subsequent electrocorticography from subdural electrodes confirmed spike and seizure onset over this region. This approach, i.e. the combination of EEG-triggered fMRI and 3D EEG source analysis, represents a promising additional tool for presurgical epilepsy evaluation allowing precise non-invasive identification of the epileptic foci.

EEG-Triggered Functional MRI in Patients With Pharmacoresistant Epilepsy

Functional magnetic resonance imaging (fMRI) triggered by scalp electroencephalography (EEG) recordings has become a promising new tool for noninvasive epileptic focus localization. Studies to date have shown that it can be used safely and that highly localized information can be obtained. So far, no reports using comprehensive clinical information and/or long‐term follow‐up after epilepsy surgery in a larger patient group have been given that would allow a valuable judgment of the utility of this technique. Here, the results of 11 patients with EEG‐triggered fMRI exams who also underwent presurgical evaluation of their epilepsy are given. In most patients we were able to record good quality EEG inside the magnet, allowing us to trigger fMRI acquisition by interictal discharges. The fMRI consisted of echoplanar multislice acquisition permitting a large anatomical coverage of the patients brain. In 8 of the 11 patients the exam confirmed clinical diagnosis, either by the presence (n = 7) or absence (n = 1) of focal signal enhancement. In six patients, intracranial recordings were carried out, and in five of them, the epileptogenic zone as determined by fMRI was confirmed. Limitations were encountered a) when the focus was too close to air cavities; b) if an active epileptogenic focus was absent; and c) if only reduced cooperation with respect to body movements was provided by the patient. We conclude that EEG‐triggered fMRI is a safe and powerful noninvasive tool that improves the diagnostic value of MRI by localizing the epileptic focus precisely. J. Magn. Reson. Imaging 2000;12:177–185.

TOXOPLASMA ENCEPHALITIS IN PATIENTS WITH THE ACQUIRED IMMUNODEFICIENCY SYNDROME

Among 504 cases of AIDS diagnosed between 1983 and 1990, there were 86 patients (17%) with toxoplasma encephalitis (TE). All were symptomatic at the time of diagnosis. General signs such as fever, neck stiffness, or headache were present in 87.2%, and 75.6% had focal signs. The primary means of diagnosis was computerized tomographic scanning, revealing 169 lesions of which 80% were immediately contrast-enhancing. All patients had IgG antibodies against Toxoplasma gondii either before (74 of 75 evaluable patients) or at the time of diagnosis of TE (73 of 75). Elevated antibody titers were present in 44% of evaluable patients, compared to 11% of patients with AIDS and other opportunistic infections. Initial treatment was pyrimethamine plus sulfonamides in 65 patients, and pyrimethamine plus clindamycin in 12 patients, with other combinations or no treatment accounting for the remainder. Life-table analysis of the time to discontinuation of treatment because of suspected side effects suggested that sulfadiazine was significantly more toxic, with 48% of patients experiencing an interruption in treatment after 30 days, than pyrimethamine (12%) or clindamycin (24%). The 30-day mortality rate was 12%, and median survival was 310 days after diagnosis, 530 in patients treated with zidovudine and 190 days in those not so treated. Of 82 evaluable patients, 16 relapsed once and 4 of these more than once. The risk of relapse was 27% 1 year after diagnosis of a first episode of TE.

High-resolution and functional magnetic resonance imaging of the brachial plexus using an isotropic 3D T2 STIR (Short Term Inversion Recovery) SPACE sequence and diffusion tensor imaging

This technical note demonstrates the relevance of the isotropic 3D T2 turbo-spin-echo (TSE) sequence with short-term inversion recovery (STIR) and variable flip angle RF excitations (SPACE: Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) for high-resolution brachial plexus imaging. The sequence was used in 11 patients in the diagnosis of brachial plexus pathologies involving primary and secondary tumors, and in six volunteers. We show that 3D STIR imaging is not only a reliable alternative to 2D STIR imaging, but it also better evaluates the anatomy, nerve site compression and pathology of the plexus, especially to depict space-occupying tumors along its course. Finally, due to its appropriate contrast we describe how 3D-STIR can be used as a high-resolution mask to be fused with fraction of anisotropy (FA) maps calculated from diffusion tensor imaging (DTI) data of the plexus.

Parenchymal abnormalities associated with developmental venous anomalies

IntroductionTo report a retrospective series of 84 cerebral developmental venous anomalies (DVAs), focusing on associated parenchymal abnormalities within the drainage territory of the DVA.MethodsDVAs were identified during routine diagnostic radiological work-up based on magnetic resonance imaging (MRI) (60 cases), computed tomography (CT) (62 cases) or both (36 cases). Regional parenchymal modifications within the drainage territory of the DVA, such as cortical or subcortical atrophy, white matter density or signal alterations, dystrophic calcifications, presence of haemorrhage or a cavernous-like vascular malformation (CVM), were noted. A stenosis of the collecting vein of the DVA was also sought for.ResultsBrain abnormalities within the drainage territory of a DVA were encountered in 65.4% of the cases. Locoregional brain atrophy occurred in 29.7% of the cases, followed by white matter lesions in 28.3% of MRI investigations and 19.3% of CT investigations, CVMs in 13.3% of MRI investigations and dystrophic calcification in 9.6% of CT investigations. An intracranial haemorrhage possibly related to a DVA occurred in 2.4% cases, and a stenosis on the collecting vein was documented in 13.1% of cases. Parenchymal abnormalities were identified for all DVA sizes.ConclusionBrain parenchymal abnormalities were associated with DVAs in close to two thirds of the cases evaluated. These abnormalities are thought to occur secondarily, likely during post-natal life, as a result of chronic venous hypertension. Outflow obstruction, progressive thickening of the walls of the DVA and their morphological organization into a venous convergence zone are thought to contribute to the development of venous hypertension in DVA.

New approaches in imaging of the brachial plexus

Imaging plays an essential role for the detection and analysis of pathologic conditions of the brachial plexus. Currently, several new techniques are used in addition to conventional 2D MR sequences to study the brachial plexus: the 3D STIR SPACE sequence, 3D heavily T2w MR myelography sequences (balanced SSFP=CISS 3D, True FISP 3D, bFFE and FIESTA), and the diffusion-weighted (DW) neurography sequence with fiber tracking reconstruction (tractography). The 3D STIR sequence offers complete anatomical coverage of the brachial plexus and the ability to slice through the volume helps to analyze fiber course modification and structure alteration. It allows precise assessment of distortion, compression and interruption of postganglionic nerve fibers thanks to the capability of performing maximum intensity projections (MIP) and multiplanar reconstructions (MPRs). The CISS 3D, b-SSFP sequences allow good visualization of nerve roots within the spinal canal and may be used for MR myelography in traumatic plexus injuries. The DW neurography sequence with tractography is still a work in progress, able to demonstrate nerves tracts, their structure alteration or deformation due to pathologic processes surrounding or located along the postganglionic brachial plexus. It may become a precious tool for the understanding of the underlying molecular pathophysiologic mechanisms in diseases affecting the brachial plexus and may play a role for surgical planning procedures in the near future.

Therapeutic decision and management of aneurysmal subarachnoid haemorrhage based on computed tomographic angiography.

The purpose of this study was to evaluate the potential of high quality computed tomographic angiography (CTA) to replace digital subtraction angiography (DSA) in cases of ruptured saccular aneurysms and perform early surgical clipping or coiling on the basis of CTA alone. In a prospective study, 100 patients with aneurysmal subarachnoid haemorrhage (SAH) diagnosed by computed tomography underwent CTA. CTA revealed a total of 118 aneurysms including all ruptured aneurysms. A decision of direct surgical clipping, endovascular coiling or therapeutic abstention was made in 89 cases (89%) on the basis of CTA alone. Sixty-one direct surgical procedures were performed after CTA. Twenty-six cases underwent DSA for immediate endovascular treatment of the ruptured aneurysm. In 11 cases (11%), a DSA was performed prior to the therapeutic decision because of unclear aneurysm. Four cases were not treated because of initial poor clinical grade. The surgical findings were compared with CTA data and were considered accurate in all but one case. All patients underwent postoperative DSA within 10 days after SAH. The sensitivity and the specificity of CTA for the detection of all aneurysms, as compared with postoperative DSA, were 95.1 and 100%, respectively. A total of six unruptured aneurysms were missed initially, but were visible retrospectively on CTA in all but one case and were found in patients with multiple aneurysms in whom the ruptured aneurysm was detected by CTA. Current quality CTA allows reliable pretreatment planning for the majority of cases of aneurysmal subarachnoid haemorrhage and diminishes the pretreatment evaluation time critically. Complementary pretreatment DSA is required in situations where CTA characteristics of the ruptured aneurysm is unsatisfactory.

The various MRI patterns of pituitary apoplexy.

Abstract. The aim of this study was to describe the various MRI features, in correlation to surgical and pathological findings, in patients who presented with pituitary apoplexy (PA). Eleven patients presenting with PA, were evaluated with various MR protocols including spin-echo (SE) T1-weighted sequences in 9 of 11 patients, post gadolinium SE T1-weighted sequences in only 8 of 11 patients, and with T2-weighted SE sequences in 2 of 11 patients. All patients had transsphenoidal pituitary surgery after MR studies. The severity of presenting symptoms ranged from headaches to coma. Ten patients had pituitary macroadenoma; one had a non-hemorrhagic metastatic lesion into a non-adenomatous pituitary gland. Of the 11 patients, one was studied at the acute stage of PA (1 day after onset), 9 at the subacute period (3–15 days after onset), and one at the late stage (5 months after onset). Images compatible with intratumoral hemorrhage were found in all macroadenomas, whereas the metastatic pituitary lesion did not show evidence of bleeding. All gadolinium-enhanced studies showed partial tumoral enhancement. The SE T2-weighted studies demonstrated areas of low and high signal intensities in keeping with the presence of blood degradation contents. Pituitary apoplexy present with different MR features, including hemorrhagic and non-hemorrhagic characteristics on T1-weighted images. Gadolinium-enhanced images do not provide complementary diagnostic information when the presence of blood is assessed on plain images.

Combination of event-related fMRI and diffusion tensor imaging in an infant with perinatal stroke.

Focal ischemic brain injury, or stroke, is an important cause of later handicap in children. Early assessment of structure-function relationships after such injury will provide insight into clinico-anatomic correlation and potentially guide early intervention strategies. We used combined functional MRI (fMRI) with diffusion tensor imaging (DTI) in a 3-month-old infant to explore the structure-function relationship after unilateral perinatal stroke that involved the visual pathways. With visual stimuli, fMRI showed a negative BOLD activation in the visual cortex of the intact right hemisphere, principally in the anterior part, and no activation in the injured hemisphere. The functional activation in the intact hemisphere correlated clearly with the fiber tract of the optic radiation visualized with DTI. DTI confirmed the absence of the optic radiation in the damaged left hemisphere. In addition, event-related fMRI (ER-fMRI) experiments were performed to define the characteristics of the BOLD response. The shape is that of an inverted gamma function (similar to a negative mirror image of the known positive adult BOLD response). The maximum decrease was reached at 5-7 s with signal changes of -1.7 +/- 0.4%.Thus, this report describes for the first time the combined use of DTI and event-related fMRI in an infant and provides insight into the localization of the fMRI visual response in the young infant and the characteristics of the BOLD response.

Reversible Cytotoxic Edema in the Splenium of the Corpus Callosum Related to Antiepileptic Treatment: Report of Two Cases and Literature Review

Summary:  Purpose: Clinically silent lesions localized in the splenium of the corpus callosum (SCC) are a rare finding in the magnetic resonance imaging (MRI) of patients receiving antiepileptic drugs (AEDs). They are usually of benign character but may induce unnecessary complementary examinations if their nature is unrecognized. So far, 22 cases have been described in the literature, for which different etiologies have been proposed. We describe two further cases and discuss the probable lesion etiology.