McRae line is a radiographic line drawn on a lateral skull radiograph or on a midsagittal section of CT or MRI that connects the anterior and posterior margins of the foramen magnum (basion to opisthion).
- indicates the presence of basilar invagination (atlantoaxial impaction): the tip of the odontoid process is normally about 5 mm below this line; basilar invagination is diagnosed when the tip crosses this line
- helps to measure the cerebellar tonsillar position: normal is above the foramen magnum
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