Post-mortem high-resolution MRI of the spinal cord in multiple sclerosis: a correlative study with conventional MRI, histopathology and clinical phenotype.

We used high-resolution MRI to study the post-mortem appearance of spinal cord multiple sclerosis in relation to histopathology and low-resolution images. Fifty-nine 3 cm long formalin-fixed spinal cord specimens from 19 multiple sclerosis patients and three controls were studied. Clinical characteristics of each patient were reviewed. High-field MRI consisted of proton-density weighted spin-echo imaging with an in-plane resolution of 80 microm. Specimens were also imaged at 1.0 T, with 1 mm pixel resolution. After MRI, the specimens were cut at 5 mm intervals and stained for myelin (Luxol fast blue/cresyl violet) and axons (Bodian method). Two observers scored the MRIs for abnormalities and divided them into (i) well-delineated areas of high signal intensity (SI) and (ii) poorly defined areas of mildly increased SI. Abnormalities were scored semiquantitatively, white matter and grey matter separately. In 81 sections the total area of abnormalities per section was measured on both histopathology sections and on matched high-field MRIs. Abnormalities ranged from just a few abnormal areas to complete involvement of the spinal cord specimen. Patients with an aggressive disease course had more abnormalities than patients with a mild or intermediate disease course. Areas of mildly increased SI were seen in all specimens, and were often found around focal high-SI lesions. However, in six patients, areas of mildly increased SI were the predominant finding on the MRIs, correlating with a primary progressive disease course. Histopathologically, high-SI areas correlated with complete demyelination, while mildly increased SI corresponded with partial demyelination. All areas scored as abnormal by the neuropathologist were also found on the MRIs, and sizes measured using both methods correlated well (r = 0.85, P<0.01). On conventional MRIs, abnormalities could be recognized fairly well. However, better differentiation could be made between high-SI and mildly increased SI abnormalities on the 4.7 T images. In conclusion, high-resolution MRI revealed a great range of abnormalities in spinal cord multiple sclerosis, which related to disease course during life. Furthermore, we found very good correlation between the extent of abnormalities shown by histopathology and the SI changes on proton-density MRIs, mainly relating to demyelination revealed histopathologically.