Clinical Imaging Exam 1 Practice

When evaluating basilar invagination on lateral skull radiographs, using a line that rests on stable, easy-to-identify landmarks makes the measurement more reproducible. McGregor's line fits this well: it is drawn from the posterior edge of the hard palate to the most caudal point of the occipital curve. This pairing of landmarks is relatively consistent across patients and radiographic projections, so different clinicians are more likely to reproduce the same line on subsequent films. The important part is the position of the tip of the dens relative to that line. If the odontoid process projects above McGregor's line by about 4.5 mm or more, basilar invagination is suggested. This threshold, combined with reliable landmarks, gives McGregor's line both accuracy and reproducibility, which is why it’s favored over other lines that rely on less stable or more variably identifiable points. Other lines depend on landmarks that can be harder to pinpoint consistently on radiographs or are more affected by head position, which reduces reproducibility. So the best choice is McGregor's line.