Figure 4

Sagittal skull base-C1/2 3DCT scan showed significant downward displacement of the clivus onto the foramen magnum. Wachenheim- Clivus line* was extremely deviated from its norms (line-a). McGregor line** was not applicable but it showed a reverse mechanism of eminent brain insult. *This line is drawn down posterior surface of clivus and its inferior extension should barely touch posterior aspect of odontoid tip (this relationship does not change in flexion and extension). If this line runs behind the odontoid, posterior subluxation has occurred.**This line is to assess whether basilar invagination exists. It is usually drawn from posterior hard palate to base of occiput. If the odontoid process is more than 4.5 mm, this reflects basilar invagination. In our patient the line intersects with the tip of clivus (basion) i.e. prolapse of the clivus onto the foramen magnum secondary to osteolysis of the skull base bony components. As our patient presented with a progressive deformity of the craniocervical and the spine, we might refer to a long posterior fusion with rigid instruments, combined with radiation therapy.