Pseudocysts and retention cysts of the maxillary sinus.

The dome-shaped radiopaque shadows frequently seen on the floor of the maxillary sinus, and sometimes inaccurately referred to as antral mucoceles, appear to represent focal accumulation of inflammatory exudate that lifts the epithelial lining of the sinus and the periosteum away from the underlying bone to form the characteristically shaped structures. Their histologic appearance is therefore that of normal or inflamed maxillary sinus lining. There is no epithelium-lined cavity present beneath the sinus mucosa; consequently, the term pseudocyst of the maxillary sinus is advocated. Less commonly, epithelium-lined retention cysts, similar to those of the minor salivary glands, are found, but mucoceles of the type found in the oral cavity apparently do not occur in the maxillary sinus.