Figure 2

3 D sagittal CT scan showed a hypertrophied clivus.Line (A) is the Wachenheim clivus line (a method to evaluate and assess craniocervical junction abnormality), for which a line drawn along the posterior aspect of the clivus toward the odontoid process. In normal individuals the line must intersect/ tangential to the odontoid. In our present patient the line is remarkably deviating, outlining the existence of significant craniocervical abnormality. Line (B) is McRae’s line, which is essentially a measurement across the foramen magnum, and is drawn from the tip of clivus (basion) to opisthion (posterior margin of foramen magnum). McRae’s line is generally longer than 30 mm in normal individuals. A diameter of less than 25 mm is almost always associated with neurological abnormalities. In our patient McRae’s line showed a length of 19.6 mm. Line (C) is McGregor’s line, which is drawn from the posterior edge of the hard palate to the most caudal point of the occipital curve. An odontoid tip extending more than 4.5 mm above this line is considered abnormal. In our patient the hyperplastic clivus (the basion) is reversing the mechanism by extending downwards and joining the cephalad part of the odontoid.