An 86-year-old female visited the Department of Otolaryngology, Head and Neck Surgery at the Veterans Medical Center, presenting with a protruding, non-fixed, well-circumscribed, round 10×10 cm mass on her left anterior midface, which had been gradually growing for 8 months. The patient had past medical history of hypertension but there was no history of sinusitis, allergy, maxillary fracture and surgery including Caldwell-Luc procedure. On gross inspection, the superior boundary of the mass extended to the lower edge of the orbit, while the lateral boundary exceeded the lateral wall of the maxillary bone. The medial margin of the mass surpassed her left nasolabial fold, disfiguring external nose near the left ala (
Fig. 1). Within the oral cavity, visible expansion of the mass onto the gingivobuccal sulcus area was also observed. Despite notable external disfigurement, the mass consistency lacked the firmness of malignant tumor. Similarly, the disruption of skin integrity, including necrosis, was also not observed. Additionally, there were no ocular movement abnormalities including diplopia, visual impairment, or facial paralysis. Left endoscopic examination initially demonstrated no visible bony destruction within the lateral wall of the nasal cavity; however, computed tomography of the paranasal sinuses with contrast enhancement did confirm that the lesion (6.8×7.2× 6.1 cm) had also caused bone remodeling and destruction of the anterior and posterior bony walls of the maxillary sinus, ultimately suggesting either a sinus mucocele or malignant neoplastic lesion (
Fig. 2). After receiving consent for surgery under general anesthesia, we explored the mass using the Caldwell-Luc approach because mass was vary extensive. A 4 cm incision was made on the gingiva-buccal folds to elevate and dissect the subcutaneous fat and facial muscles. Underneath, well defined cystic wall came into view. Before the cyst removal, aspiration of cyst was performed. Approximately 100 cc of viscous liquefacted mucus containing sand-like melted bone dust was obtained, but not cultured. In order to preserve the cystic wall, the cyst was then meticulously dissected to separate it from the overlying soft tissue as well as or the bony wall of the maxillary sinus. Cyst was then further detached from the upper, lower, and lateral sides of the maxillary sinus (
Fig. 3A). During the mass removal, we noticed that the mass had completely eroded through the anterior bone of the maxillary sinus, leaving the area wide open after removal. Similarly, the superior wall of the maxillary sinus was also noted to have been destroyed, demonstrated by the visualization of the inferior periosteum of the left orbit as well as the visible herniation of the inferior aspect of the entire orbit when gentle pressure was applied against the eyeball. On pathological examination, the cells surrounding the cyst and mucinous material were confirmed to be respiratory epithelial cells, and the final diagnosis by permanent biopsy was confirmed to be a sinus mucocele (
Fig. 3B and C). The patient had no recurrence as of 2 years after the surgery.