<prompt> Sinusitis which is least involved is?MaxillaryEthmoidFrontalSphenoid  <response>: Sinusitis is least involved in the sphenoid sinus. Isolated involvement of this sinus is rare. Its 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 