<prompt> True about sphenoid sinus -Lined by stratified squamous epitheliumDuct open in middle meatusOpen in sphenoethmoid recessPresent at birth  <response>: All paranasal sinuses are lined by respiratory epithelium i.e. ciliated pseudo stratified columnar epithilium i.e. option a is incorrect.Sphenoid sinus: Important pointsIt is not present at birthIt occupies the body of sphenoidOstrum of sphenoid sinus is situated in the upper part of anterior wall and drains into spheno ethmoidal recess.On x ray: Sphenoid sinus is visible by 4 years of age. 