From the case:
Assessment of basilar invagination
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Frontal Image
- Digastric line - tip of odontoid process is normally located 11 mm below this line.
- Bimastoid line - tip of odontoid process projects normally not more than 10 mm above this line.
Lateral Image
- McRae line - tip of odontoid process normally projects below this line
- Chamberlain line - tip of odontoid process projects normally not more than 3 mm above this line.
- McGregor line - tip of odontoid process projects normally not more than 5 mm above this line.