The radiographic assessment of basilar invagination can be assessed by observing relative position of tip of odontoid process on frontal and lateral view of skull on x ray as well as on the coronal and sagittal planes on CT.
Coronal Image
- Digastric line (yellow line) - tip of odontoid process is normally located 11 mm below this line.
- Bimastoid line (blue line) - tip of odontoid process projects normally not more than 10 mm above this line.
Sagittal Image
- McRae line (red line) - tip of odontoid process normally projects below this line
- Chamberlain line (green line) - tip of odontoid process projects normally not more than 3 mm above this line.