Measurements of the normal cervical spinal cord on MR imaging.

The purpose of this study was to determine normal measurements of the C1-T3 spinal cord in anteroposterior and transverse planes from MR images and to compare these with previously published data. Seven hundred and fifty-six measurements were made from 66 randomly selected MR studies of the cervical spine. We measured the anteroposterior and transverse diameters of the cord at each vertebral level and computed the simple product of these diameters to provide a single useful numerical value, termed the approximate cord area (ACA). The cord varies in average anteroposterior and transverse diameters from 8.8 mm x 12.4 mm at C2 to 8.7 mm x 14 mm at C4 to 7.4 mm x 11.4 mm at C7. The cervical enlargement was found from C4 to C6 and was most evident by comparing the ACA values. At C2 the average ACA was 110 mm2, at C4 it was 121.9 mm2, and at C7 the average ACA was 84.6 mm2. Comparison of our data with the literature reveals disparate measurements that vary up to 6 mm from our mean values. However, our results correlated well with the postmortem studies of Nordquist (1964). A single number cannot be used as the basis for evaluating spinal cord size. Each level should be compared with the normal range specific for that level.