This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Which structure is NOT seen in standard Occipitomental (Water's) view 
Select and explain. 
A. Anterior ethmoid air cells, B. Posterior ethmoid air cells, C. Maxillary sinus, D. Sphenoid sinus
B: Posterior ethmoid air cells
Answer: B: Posterior ethmoid air cells 
Explanation: Ans. is 'B Posterior ethmoidal and cannot be visualized. Hence single best answer is posterior ethmoidal sinus. First read these lines from Burrow & Leeds " Occipitomental (Water's) projection: was developed more than 50 years ago by an ENT surgeon, as a modification of the original PA view of the skull, to examine the maxillary antrum and other accessory sinuses. It provides the only linen cohered view of the antra , which are projected above the petrous pyramids. The view of the bony orbits is second only in value to that given by the Caldwell's view. Only in this projection are the ethmoidal cells separated: the anterior ones are projected above, the posterior ones below."