In the SMV projection of the sinuses, with a horizontal beam, which anatomical structure is superimposed by the anterior frontal bone?

• A. Mental protuberance
• B. Nasion
• C. Glabella
• D. Suprorbital margin

Answer: (A)

This question tests how superimposition appears in the submento-vertebral (SMV) view of the sinuses when the beam is horizontal. In this projection the x-ray beam enters under the chin and travels upward toward the vertex, with the anterior surface of the frontal bone lying in front of deeper midline structures.

Because the frontal bone sits anteriorly, it can overlay structures located inferomedially toward the chin on this view. The chin area, or mental protuberance, is the structure most likely to be obscured by or superimposed by the frontal bone in a horizontal SMV projection. The other landmarks listed (nasion, glabella, supraorbital margin) are part of or very near the frontal bone itself and do not lie in the path that would be specifically overlapped by the anterior frontal bone in this view.