What is the CR angle for the PA axial oblique projection of the cervical intervertebral foramina?

The AP oblique cervical spine projections are supplementary views to the standard AP, odontoid and lateral images in the cervical spine series and are always done bilaterally for comparison purposes. However, the PA oblique projection is preferred as it reduces radiation dose to the thyroid 1 compared to the AP oblique projection.

This projection can be used to visualize pathology involving the adjacent soft tissue structures or cervical spine, especially stenosis of the intervertebral foramina.

Note: Such views should not be performed on trauma patients without the strict instructions of a qualified clinician who has reviewed the lateral cervical spine image or CT of the cervical spine. Moving the patient's head or neck, or removing a cervical collar could be detrimental.

• patient is standing erect with either the left or right posterior side closer to the image receptor
• the thorax and cervical spine is at 45° to the image receptor
• the face is in a lateral position with the interpupillary line perpendicular to the image receptor 

• anteroposterior oblique
• centering point
  • C4 at or just above the level of the hyoid bone
  • 15° cranial tilt of the central ray
•  collimation
  • laterally to include the entire cervical spine and its spinous processes
  • anteriorly to include the soft tissue of the neck
  • superiorly to include all of C1/base of skull
  • inferiorly to include to at least T1 (EAM to sternal notch)
•   orientation
• detector size
•  exposure
•  SID
• grid

• all of the cervical spine should be included from C1-T1
• patient’s head should be in a lateral position to prevent  mandibular superimposition over the vertebral bodies of the cervical spine
• intervertebral foramina of the side positioned further from the image receptor should be demonstrated open  

• make sure that any removable artefacts such as earrings, glasses or metal dentures are removed to avoid obscuring the anatomy of interest.
• using a larger source to image distance will decrease the magnification of the image and improves acuity 2
• remember that for AP Oblique cervical spine positioning the patient will either be in an RPO or LPO position and that posterior obliques demonstrate the foramina opposite to your patient positioning 4
  • for example, an LPO will demonstrate the right foramina

To demonstrate the intervertebral foramen of the c-spine open, it is necessary to achieve adequate rotation of the vertebral column, usually at 45°.

If underrotated, the foramina will be narrowed and a sternoclavicular joint would be superimposed over the vertebral column 3.

Over rotation of more than 45° would cause one pedicle to be foreshortened while the other pedicle aligns to the midline of the vertebral bodies 2.

• 1. John Lampignano, Leslie E. Kendrick. Bontrager's Textbook of Radiographic Positioning and Related Anatomy. (2017) ISBN: 9780323399661
• 2. Eugene D. Frank, Bruce W. Long, Barbara J. Smith, Vinita Merrill. Merrill's Atlas of Radiographic Positioning and Procedures. (2020) ISBN: 9780323073219
• 3. Kathy McQuillen Martensen. Radiographic Image Analysis. (2014) ISBN: 9780323280525
• 4. Pate D. Obliques: Which Foramen Are We Looking At? [Internet]. Dynamicchiropractic.com. 2017 [cited 20 February 2017]. Available from: http://www.dynamicchiropractic.com/mpacms/dc/article.php?id=31483

What is the proper Cr angle and direction for the AP oblique projections of the cervical spine?

Where does the CR enter the patient for the AP oblique projection?

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