This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Head and neck, Subject name: Anatomy
Sphenoid sinus drains into which of the following 
Select and explain. 
A. Spheno-ethmoidal recess, B. Middle meatus, C. Superior meatus, D. Hiatus semilunaris
A: Spheno-ethmoidal recess
Answer: A: Spheno-ethmoidal recess 
Explanation: The right and left sphenoidal air sinuses lie within the body of sphenoid bone. They are separated by a septum. The two sinuses are usually unequal in size Each sinus opens into the sphenomandibular recess of corresponding half of the nasal cavity. Ref BDC volme3,6th edition pg 246