Which cranial positioning line should be perpendicular to the IR if the patient is unable to flex their neck for an AP axial Towne skull?

Which cranial positioning line should be perpendicular to the IR if the patient is unable to flex their neck for an AP axial Towne skull?

• A. Orbitomeatal line (OML)
• B. Infraorbitomeatal line (IOML)
• C. Glabellomeatal line (GML)
• D. Interpupillary line (IPL)

Answer: (B)

In the AP axial Towne skull projection, how you orient the skull relative to the image receptor determines the angle you angle the centric ray to project the posterior fossa (including the foramen magnum). When the neck can be flexed, you make the orbitomeatal line (OML) perpendicular to the IR and use a caudal angle of about 30 degrees. But if the patient cannot flex the neck, you adjust by aligning a different cranial line to be perpendicular to the IR—the infraorbitomeatal line (IOML). With IOML perpendicular to the IR, the required CR angle becomes steeper (about 37 degrees caudal) to achieve the same projection of the occipital region. So the line that should be perpendicular to the IR in a patient who cannot flex the neck is the infraorbitomeatal line. This ensures the x-ray beam is correctly angled to visualize the desired posterior fossa structures despite restricted neck flexion.

In the AP axial Towne skull projection, how you orient the skull relative to the image receptor determines the angle you angle the centric ray to project the posterior fossa (including the foramen magnum). When the neck can be flexed, you make the orbitomeatal line (OML) perpendicular to the IR and use a caudal angle of about 30 degrees. But if the patient cannot flex the neck, you adjust by aligning a different cranial line to be perpendicular to the IR—the infraorbitomeatal line (IOML). With IOML perpendicular to the IR, the required CR angle becomes steeper (about 37 degrees caudal) to achieve the same projection of the occipital region.

So the line that should be perpendicular to the IR in a patient who cannot flex the neck is the infraorbitomeatal line. This ensures the x-ray beam is correctly angled to visualize the desired posterior fossa structures despite restricted neck flexion.