A secretion cyst, not usually seen radiographically, that is caused by blockage of the seromucinous gland duct. As secretions collect, they expand the duct, producing a cyst that is encompassed by respiratory or cuboidal epithelium. It may be located on the sinus floor, near the ostium, or within antral polyps. It may be caused by sinus infections, allergies, or odontogenic infections.