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The form and distribution of MRI abnormalities in 114 patients with clinically definite multiple sclerosis (MS) have been compared with observations on 53 apparently healthy individuals, 129 patients with isolated focal neurological lesions with which MS often presents (51 patients with optic neuritis, 44 with isolated brainstem lesions and 34 with isolated spinal cord syndromes) and 105 patients with disorders which may be confused clinically or radiologically with MS. The latter comprised 55 patients with cerebral vascular disease (including 7 cases of dementia with diffuse white matter disease), 24 with degenerative ataxic disorders, 8 with cerebellar tonsillar ectopia, 7 with sarcoidosis and 11 with a variety of other disorders. Periventricular abnormalities were found in all but 2 patients with MS and discrete white matter lesions in all but 12. Characteristically the periventricular changes in MS were irregular in outline. Periventricular abnormalities which were often milder and of smooth outline were seen in 37/55 patients with cerebral vascular disease, 9/24 with cerebellar degeneration, 5/7 with sarcoidosis and in 2/3 apparently healthy individuals over the age of 60. The appearances in the 7 cases of dementia resembled those with advanced MS. Cerebellar and/or brainstem atrophy characteristic of the cerebellar degenerations, in the absence of white matter abnormalities, was helpful in making the distinction from MS. Congenital anomalies and tumours in the region of the brainstem and foramen magnum were readily shown. More than half the patients with symptoms attributable to isolated focal neurological lesions had additional lesions at presentation. MS cannot be diagnosed in these cases at presentation, but repeat scans after 5 to 20 months in 25 patients with optic neuritis and 10 with clinically isolated brainstem lesions have shown new lesions in 7 (20%). The patients with new lesions fulfil the criteria for clinically probable MS (Poser et al., 1983). Measurements of T1 and T2 in vivo permitted the distinction of acute from chronic brainstem lesions. There were quantitative differences in T1 and T2 between the normal appearing white matter in MS and normal brain. Studies of postmortem brains provided convincing evidence that the MRI abnormalities in MS correspond with plaques. Evidence is adduced to support the view that an important source of the abnormal NMR signals in acute lesions is oedema, and in chronic lesions is gliosis; demyelination per se is unlikely to make an important contribution.

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Magnetic resonance imaging (MRI) of the optic nerves using the STIR (short inversion time inversion recovery) sequence was performed in 37 adult patients with a recent or past attack of optic neuritis. MRI revealed high-signal regions in 84% of symptomatic and 20% of asymptomatic nerves. The mean longitudinal extent of lesions was 1 cm. Slow or poor visual recovery was associated with more extensive lesions, or lesions within the optic canal. Disk swelling was usually associated with anterior lesions but also occurred with lesions in the canal. Visual evoked potentials were even more sensitive than MRI in detecting lesions and are still the investigation of choice in suspected demyelinating disease involving the optic nerve.

Pattern evoked responses have been recorded in 19 patients with compression of the optic nerve, chiasm or tract, verified at operation. These included 4 patients with orbital tumours, 5 with intracranial meningiomas, 2 with craniopharyngiomas and 8 with pituitary tumours. The evoked response was abnormal in all except one of these patients. The pattern of abnormalities in the response, however, differed from that in the earlier series of patients with primary demyelinating disease. The incidence of delayed responses was much lower, and the magnitude of the delays was smaller. Absent responses were particularly characteristic of patients with intracranial meningiomas. Tumours arising in the region of the sella turcica were associated with a high incidence of abnormalities of the waveform of the response, and asymmetry of the field of the occipital evoked potential was especially characteristic of this group. Most, but not all, asymmetric cases were associated with field defects.