Residual Cyst Mimicking an Aggressive Neoplasm—A Life-Threatening Condition

Odontogenic cysts are frequently encountered in clinical practice. However, residual cysts, a specific type of inflammatory odontogenic cyst, are relatively rare. These cysts may slowly expand over time, damaging surrounding soft tissues and bone, typically without posing a threat to life. We report the case of a 67-year-old man with liver failure and a cystic tumor in his right maxilla that had invaded his oral cavity and cheek, causing nasal obstruction and severe bleeding following an incisional biopsy. A computed tomography (CT) scan of the mass was nonspecific, and an initial histopathological analysis of the tissues was inconclusive due to chronic inflammation and hemorrhagic alterations, complicating the diagnostic pathway. The suspicion of a potentially aggressive malignant neoplasm and the need for immediate intervention due to bleeding necessitated a tracheotomy, tumor removal, percutaneous endoscopic gastrostomy, and transfusions of red blood cells. A subsequent histopathological examination revealed features indicative of a residual cyst. The entire lesion was excised through functional endoscopic sinus surgery. The surgical treatment was performed safely and effectively. Follow-up CT confirmed complete removal of the lesion. This case highlights a rare yet possible complication of odontogenic cysts and underscores the necessity of early diagnosis and comprehensive prophylaxis to prevent severe complications.