EBM Consult

McGregor Line on Radiographic Image


  • The McGregor line is used when the opisthion (posterior aspect of the foramen magnum) cannot be identified on a plain radiograph in an attempt to draw the Chamberlain line. The line can also be used on CT scan and MRI.
  • It is made be drawing a line that connects the posterior edge of the hard palate to the most caudal portion of the occipital curve. 
  • If the tip of the dens (odontoid process) extends more than 4.5 mm above this line it is concerning for a basilar invagination.

McGregor Line

    Radiogrphic (X-Ray) Image: McGregor Line

    McGregor Line Image

    Related Content

    To see other related content please select an item below:


    McRae Line           Chamberlain Line    Wackenheim Line     Lateral X-Ray  

    1. Kwong Y et al.  AJR Am J Roentgenol 2011;196(4):W421-5. PubMed 
    2. Cronin CG et al. Clin Radiol 2009;64(1):64-9. PubMed


    Editors & Reviewers

    Editors:  Anthony J. Busti, MD, PharmD, FNLA, FAHA
    Last Updated:  June 2015