Background: The mucous retention cyst of maxillary sinus results from either a pathologic secretory duct blockage or a cystic degeneration. Most of them develop unilaterally, but may occur bilaterally. Retention cysts requires no treatment. In symptomatic lesions, however, it must be removed by surgical treatment.

Objective: To report a clinical case of large bilateral retention cysts accidentally found in a young male patient treated by total enucleation.

Case Report: The authors reported on a young male patient of mucous retention cysts in left and right maxillary sinuses.

Results: Panoramic radiograph, postero-anterior skull projection, lateral cephalometric radiograph, and computed tomography (CT) showed the typical radiographic features of mucous retention cysts. All specimens illustrated the histopathologic features of sinus lining overlying edematous connective tissue.

Conclusion: Although retention cysts appear on routine radiograph examinations, CT is an alternative modality to assist in pathology differentiation. The lesion is commonly asymptomatic, however, they should be noticed and monitored to avoid complications.

Keywords: Mucous retention cyst, Retention pseudocyst, Maxillary sinus