Final answer:
To correct an AP axial Towne projection with the dorsum sella above the foramen magnum, adjust the head's rotation and angle the central ray 30 degrees caudad to the orbitomeatal line (OML) for proper image capture.
Step-by-step explanation:
When an AP (anteroposterior) axial Towne projection yields an image where the dorsum sella appears above the foramen magnum, this typically indicates an under-rotation of the head. To correct this image, the patient's head should be extended so that the central ray is properly angled. Typically, this means angling the central ray at approximately 30 degrees caudad (downward) to the orbitomeatal line (OML). This allows for the proper visualization of the foramen magnum, where the spinal cord emerges and the vertebral arteries enter the cranium, and also the structures in the forebrain region such as the cerebrum and diencephalon which develops from the prosencephalon.