Mucocele most commonly occurs

Mucoceles are dilated, mucous-containing sacs that are lined by mucous membranes and result from continuous secretions into an obstructed sinus. The frontal sinus is most commonly affected, whereas the sphenoid sinus is rarely involved. Sinus expansion with thinning and remodeling of the sinus walls occurs. When the frontal sinus is involved, as it expands downward and outward proptosis can occur. Ref : ENT textbook by Dhingra 6th edition Pgno : 198