Final answer:
The ethmoid sinus is located close to the medial wall of the orbit, making it the best choice to visualize the pyramids filling one third of the orbits. The frontal sinus, being anterior and not adjacent to the orbit, would not be as suitable for this visualization.
Step-by-step explanation:
The student asks about the best sinus to visualize in order to see the pyramids filling one third of the orbits. The paranasal sinuses include the frontal, maxillary, sphenoid, and ethmoidal sinuses - each located within specific bones of the skull. The frontal sinus is the most anterior, situated within the frontal bone above the eyebrows. The ethmoid sinus, or ethmoid air cells, are small spaces located on the right and left sides of the ethmoid bone, situated between the medial wall of the orbit and lateral wall of the upper nasal cavity.
Considering the anatomy, the ethmoid sinus is located close to the medial wall of the orbit and could potentially show the pyramids filling a third of the orbits on imaging studies. Due to its location, the ethmoid air cells would give the clearest indication of this condition. The frontal sinus, being more anterior, would not be the best option for visualizing the pyramids within the orbits.