Mucocele is a cyst filled with mucus that develops within
a sinus cavity as the result of occlusion of the ostium.
Most commonly it is due to infection, but may also result
from trauma or be congenital. Retained secretions
cause expansion of the sinus and bone erosion. The
most common sites of occurrence are the frontal and the
sphenoidal sinuses. The cyst is lined by respiratory epithelium
that shows prominent goblet-cell hyperplasia.
Expansion of the cyst may cause atrophy and
metaplasia of the epithelium.