Sinusitis which is least involved is?
Maxillary
Ethmoid
Frontal
Sphenoid
Sinusitis is least involved in the sphenoid sinus. Isolated involvement of this sinus is rare. It's often pa of pansinusitis or is associated with infection of posterior ethmoid sinuses. (Reference: Textbook of PL Dhingra and Shruti Dhingra; 7th edition, pg no. 216)
Nose and paranasal sinuses