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A unilocular radiolucency associated with an endodontically treated tooth should make one think of a periapical cyst. Another cyst to consider would be an odontogenic keratocyst. Lack of expansion would be more consistent with OKC but periapical cyst would be certainly considered given the endodotically treated tooth present in the area. Pain is described in both cysts if they are infected.
Given the radiographic findings of a unilocular and well-defined radiolucency, a cyst has to be on the differential diagnosis. OKC is considered high up on the differential diagnosis given the lack of expansion but the histology is not supportive of OKC.
The odontogenic keratocyst (OKC) is an aggressive odontogenic cyst, known for its rapid growth and its tendency to invade the adjacent tissues, including bone. It has a high recurrence rate and is associated with basal cell nevus syndrome. It affects patients in the age ranges of 20-29 and 40-59, but cases in patients ranging in age from 5 to 80 years have been reported. The distribution between sexes varies from equal distribution to a male-to-female ratio of 1.6:1, except in children. Odontogenic keratocysts may occur in any part of the upper and lower jaw, with the majority (almost 70%) occurring in the mandible. They occur most commonly in the angle of the mandible and ramus. Anterior maxilla is a rare location for OKC but has been described. Radiographically, OKCs present predominantly as unilocular radiolucencies with well-defined or sclerotic borders; they may also present as multilocular radiolucencies, but rarely. OKCs commonly present as a unilocular radiolucency with scalloped borders. Teeth associated with OKC are vital. OKCs grow to sizes larger than any other odontogenic cysts. They usually penetrate the bone rather than expand it and grow in an anterior to posterior direction. Despite this aggressive growth, they often remain asymptomatic, thus growing to large sizes and hollowing the bone. Treatment of choice is surgery with cauterization, especially with carnoy's solution.