Which radiographic baseline is used to position the PA axial projection (Caldwell method) of the cranium?

The correct radiographic baseline for positioning the PA axial projection (Caldwell method) of the cranium is the Orbitomeatal Line (OML). This positioning is crucial because it ensures that the x-ray beam is directed appropriately to best visualize the structures of the cranium, particularly the frontal bone and the orbit.

When using the OML, the patient's orbit and the outer canthus are aligned with the radiographic beam, allowing for accurate projection and optimal visualization of the critical anatomical landmarks. The OML helps achieve the necessary angle (usually about 15 degrees caudad) for the x-ray beam, which is essential in positioning for the PA axial projection to delineate the superior orbital fissures clearly.

Using the appropriate baseline enhances diagnostic accuracy by ensuring the correct anatomical structures are projected in the image.