Ethmoid sinus is the second most common site for paranasal sinus mucocele after frontal sinus. It is due to obstruction of the sinus ostium by secretions, inflammation or mass lesion. Sinus secretions accumulate over a long period with resultant sinus expansion, bone remodeling and thinning with local mass effect.

Ethmoid mucocele can cause proptosis (as in this case) or orbital apex compression. Superadded infection can lead to extension of the inflammatory process to nearby anatomical structures with formation of subcutaneous abscess (Pott's puffy tumor), epidural abscess or subperiosteal orbital abscess.