Radiographic assessment of basilar invagination

Five lines have been described and used by most of the radiologists to evaluate basilar invagination on frontal and lateral skull plain film as well as coronal and midsaggital reconstructed CT images.

This is based on the relative projection of odontoid process to these lines, which is as follows:

Frontal image

  • digastric line - tip of odontoid process is normally located 11 to 21 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.
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Article information

rID: 27190
System: Head & Neck
Section: Approach
Tag: pm
Synonyms or Alternate Spellings:
  • Assessment of basilar invagination

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Cases and figures

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    Figure 1: frontal
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    Figure 2: lateral
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    Case 1: Coronal bone window
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    Case 2: Sagittal bone window
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    Case 3
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