Different MRI techniques are used to investigate multiple sclerosis (MS) in vivo. The pathological specificity of these techniques is poorly understood, in particular their relationship to demyelination and axonal loss. The aim of this study was to evaluate the pathological substrate of high field MRI in post-mortem (PM) spinal cord (SC) of patients with MS. MRI was performed in PMSCs of four MS patients and a healthy subject on a 7 Tesla machine. Quantitative MRI maps (PD; T2; T1; magnetization transfer ratio, MTR; diffusion weighted imaging) were obtained. After scanning, the myelin content and the axonal density of the specimens were evaluated neuropathologically using quantitative techniques. Myelin content and axonal density correlated strongly with MTR, T1, PD, and diffusion anisotropy, but only moderately with T2 and weakly with the apparent diffusion coefficient. Quantitative MR measures provide a promising tool to evaluate components of MS pathology that are clinically meaningful. Further studies are warranted to investigate the potential of new quantitative MR measures to enable a distinction between axonal loss and demyelination and between demyelinated and remyelinated lesions.

The management and clinical course of patients with myasthenia gravis admitted to a neurological intensive therapy unit (ITU) over a 66 month period were reviewed. Twenty-seven patients were admitted in myasthenic crisis, eight of whom had multiple admissions. One patient had a cholinergic crisis and a further patient an acute myocardial infarction. A specific aetiological factor precipitating myasthenic crisis was identified in 19 instances: infection (8), reduction in medication (5), menstruation (4), and steroid administration (2). Thirteen patients with crisis had had a previous thymectomy, six with thymoma. Twenty-three out of 35 (66%) patients admitted in crisis required intubation; nine subsequently needed a tracheostomy. Twenty-nine patients received plasma exchange and seven intravenous immunoglobulin. Four patients in myasthenic crisis died in ITU [adult respiratory distress syndrome (1), disseminated intravascular coagulation and cytomegalovirus (CMV) pneumonitis (1), cardiac failure (1) and multiple organ failure (1)]. Appropriate management of myasthenia gravis requires the easy availability of specialised neuro-intensive care facilities. Copyright Rapid Science Ltd

The authors report five patients with damage to the distal spinal cord following spinal anesthesia. The patients developed leg weakness and sensory disturbance. MRI of the lumbosacral spine showed an abnormal area of high signal within the conus medullaris in all patients. Symptoms and signs persisted at 1- to 2.5-year follow-ups. Incorrect needle placement and type of needle used are possible factors leading to spinal cord injury.

To evaluate whether the lines occasionally detected on clinical magnetic resonance (MR) images are genuine hippocampal layers, a formalin fixed hippocampal specimen was scanned using T2 weighted sequences at 7 Tesla (voxel dimensions 0.064i0.064i1 mm) and at 1.5 Tesla (voxel dimensions : 0.156i0.156i1 mm) and compared with the results of histological examination. In addition, a healthy volunteer was scanned with a T2 weighted sequence at 1.5 Tesla (voxel dimensions : 0.469i0.469i2 mm). On 7 Tesla images hippocampal layers and the granule cell layer of the dentate were visible. On 1.5 Tesla images of the specimen, the hippocampal layers were again identified, but the granule cell layer of the dentate was not detectable. On 1.5 Tesla images of the hippocampus in vivo, 3 layers could be distinguished in the hippocampus on some slices. These mainly represented the alveus, pyramidal cell layer and stratum radiatum. A dark line consisting of a few pixels possibly represented the dentate gyrus. Our results show that the lines occasionally detected on clinical MR images are likely to be real hippocampal layers. However, the resolution currently used in clinical imaging (typically 0.469i0.469i2 mm or lower) is not sufficient for the detection of all hippocampal layers. For the reliable detection of all hippocampal layers on MR images an increase by a factor of approximately 20 would be necessary.Key words : Neuroimaging ; hippocampal formation. The hippocampus is a complex mesiotemporal structure consisting of several layers (Duvernoy, 1988) (Fig. 1). It plays an important role in dementia, psychosis and epilepsy. In temporal lobe epilepsy, hippocampal sclerosis is the most common underlying structural abnormality (Wolf et al. 1993). Histologically hippocampal sclerosis is characterised by cell loss and gliosis affecting mainly the pyramidal cell layer in sector CA1 (Sommers sector) (Meencke & Veith, 1991). With magnetic resonance (MR) imaging the hippocampus can be visualised and severe hippocampal sclerosis can be reliably detected (Jackson et al. 1990). Visualising the internal structure of the hippocampus on MR images to detect more subtle abnormalities has been of interest in the context of epilepsy research. On coronal MR images lines within Correspondence to Dr Udo Wieshmann, National Society for Epilepsy, MRI Unit, Chalfont St Peter, Gerrards Cross, Bucks SL9 ORJ, UK. Tel. : j441494 874646 ; fax : j 441494 875666 ; e-mail : uwiesh!ion.ucl.ac.uk the hippocampus can sometimes be identified. These lines have been interpreted as the internal structure of the hippocampus. Disruption of the internal structure has been interpreted to be a sign of hippocampal sclerosis (Jackson et al. 1993 ;Bronen, 1998). To evaluate whether these lines reflect genuine layers within the hippocampus, we have performed MR experiments at different field strength on an anatomical specimen of the hippocampus and on a volunteer. An anatomical specimen of the hippocampus was obtained by dissecting the hippocampus from...

The management and clinical course of patients with myasthenia gravis admitted to a neurological intensive therapy unit (ITU) for thymectomy over a 66 month period were reviewed. There were 53 patients, 20 male and 33 female, mean age 35.2 years (18-74) and median ITU stay of 5 days (2-30). Indications for thymectomy were thymic enlargement on computed tomography (34%), persistence of generalized symptoms (38%), a combination of both (20%), steroid side effects or dependency (4%) and progressive bulbar symptoms (4%). Following thymectomy, thymic histology revealed thymic follicular hyperplasia (26/53; 49%), atrophy (11/53; 21%), thymoma (12/53; 23%) and normal thymus (4/53; 8%). Post-operatively 23% required prolonged intubation (> 48 hrs); two patients required a tracheostomy 10 and 13 days post-operatively. Plasma exchange was required for two patients (3.8%) due to persistent severe myasthenic weakness. Three patients (6%) developed a post-operative chest infection and one pseudomembranous colitis. There were no post-operative mortalities during the study period. After 2 years, 35% of patients were in remission and 46% had ocular or mild generalized symptoms only. Thymectomy for myasthenia gravis is followed by sustained clinical improvement in the majority of patients. The appropriate post-operative management of these patients is best undertaken in a specialized neuro-intensive care setting. Copyright Rapid Science Ltd