Maxillary Sinus Retention Cyst/ Pseudocyst

Retention cysts and pseudocysts involving the lining of the maxillary antrum are common findings in panoramic radiographs. These lesions are discovered incidentally and are of little clinical significance.

Etiology and Pathogenesis

Retention cysts are thought to arise from blockage of an antral seromucous gland, resulting in a ductal epithelium-lined cystic structure filled with mucin. Pseudocysts are inflammatory in origin and result from fluid accumulation within the sinus membrane. They may be related to infection or allergy. Bacterial toxins, anoxia, or other factors presumably cause leakage of protein into surrounding soft tissue, thus raising the extravascular osmotic pressure with subsequent fluid increase. 

Clinical Features 

The great majority of these lesions are asymptomatic, although there maybe some slight tenderness in the mucobuccal fold or, more rarely, palpable buccal expansion in this region. In panoramic and periapical radiographs, retention cysts and pseudocysts of the maxillary sinus are hemispheric, homogeneously opaque, and well delineated. They usually demonstrate an attachment to the floor of the antrum, with size being a function of the anatomic space rather than of duration, Uncommonly these lesions may appear bilaterally.

Histopathology

The pathogenesis of the two forms of antral cysts is reflected in the histologic appearance. The retention cyst is lined by pseudostratified columnar epithelium with occasional mucous cells interspersed. The supportive elements are minimally inflamed. The pseudocyst shows no evidence of an epithelial lining but, rather, pools of mucoid material surrounded by slightly compressed connective tissue.

Differential Diagnosis
A clinical differential diagnosis of cysts and pseudocysts arising within the mucosa of the maxillary sinus would include polyps, hyperplasia of the sinus lining secondary to odontogenic infection, maxillary sinusitis, and neoplasms arising within the soft tissues of the antral lining.

Treatment
 Antral retention cysts and pseudocysts are generally left untreated because they are limited in growth and are not destructive, and most spontaneously rupture. Therefore periodic observation is all that is required.