In a parietoacanthial transoral projection of the sinuses, which sinuses are visualized through the open mouth?

In a parietoacanthial transoral projection, also known as the Waters view, the primary sinuses visualized through the open mouth are the maxillary sinuses. This projection is specifically designed to visualize the maxillary sinuses by aligning the x-ray beam perpendicular to the plane of the maxilla, allowing for an optimal view of these air-filled cavities.

The reason the answer identified as sphenoid is not suitable in this context is that while a proper view can allow some visualization of the sphenoid, particularly when angling the beam correctly, the transoral view primarily targets the maxillary sinuses directly. The sphenoid sinuses are typically better visualized in other projections such as the lateral or the Caldwell view.

Understanding the correct positioning and angling of the x-ray beam is crucial for effectively visualizing the various sinuses. In this case, the focus is on how the maxillary sinuses take precedence in the parietoacanthial projection when the mouth is opened.