Which two paranasal sinuses are assessed by the open-mouth Waters projection?

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

Answer: (B)

Open-mouth Waters projection uses a parietoacanthial angle with the mouth opened to separate the oral cavity from the nasal passages. This adjustment lets the x-ray beam pass through both the maxillary sinuses (which are well demonstrated in this view) and the sphenoid sinus, which sits higher and behind the nasal cavity and becomes visible when the palate is lowered by opening the mouth. The frontal and ethmoid sinuses are not as well visualized with this projection because of their position deeper within the skull and closer overlap with surrounding structures. So, the two sinuses assessed in this view are the sphenoid and maxillary sinuses.