How far anterior to the external auditory meatus (EAM) does the midsagittal plane pass through the throat when performing a submentovertex projection of the skull?

• A. .75 inch (2 cm)
• B. 1.5 inches
• C. 0.25 inch
• D. 3 inches

Answer: (A)

In a submentovertex projection, you position the head so the base of the skull and foramen magnum are well demonstrated, with the midsagittal plane aligned toward the center of the throat. The line through the throat should be a short distance in front of the external auditory meatus. That offset is about 2 cm (roughly 0.75 inch). This small anterior shift ensures the central ray, directed perpendicular to the image receptor, passes through the midline skull base structures (like the sella/foramen magnum) without rotation or overlying structures obscuring them.

If the midsagittal plane were placed too close to the EAM, or further anterior than about 2 cm, the projection could become miscentered or distorted, compromising the view of the skull base.