Which pair of sinuses is shown in the open-mouth Waters projection?

• A. Sphenoid and Maxillary
• B. Frontal and Ethmoid
• C. Sphenoid and Ethmoid
• D. Frontal and Maxillary

Answer: (A)

Open-mouth Waters is a parietoacanthial view focused on the paranasal sinuses, with the mouth opened to move the soft palate away from the nasal cavity. This positioning lets the maxillary sinuses be seen clearly and also brings the sphenoid sinuses into the field, so both are visible in the same image. The frontal sinuses and ethmoid air cells sit more anteriorly/in a different plane and are not as well demonstrated in this projection, which is why this view is particularly used to visualize the sphenoid and maxillary sinuses together.