DEFINITIONS AND CLINICAL FEATURES Paranasal sinus mucoceles are expansile cystic lesions lined by respiratory epithelium. Mucoceles are thought to develop from the obstruction of the sinus ostium with resultant accumulation of mucus, which over time expands the sinus. Blockage of the sinus ostium may occur due to a variety of reasons including local trauma, previous surgery, repeated infections, polyps, and tumors. Although rare, they are the most common expansile lesions of the paranasal sinuses. Furthermore, while benign, local expansion may thin and destroy surrounding bone leading to extension into nearby structures such as the orbit and frontal
lobe. Most mucoceles are sterile; however, if infected, a mucopyocele may develop, which has the potential to lead to meningitis or a brain abscess.