Answer: Odontogenic keratocyst

Histology: The cyst wall is lined by a stratified squamous epithelium. In areas the cyst wall is heavily inflamed. The histologic features of the lining epithelium are best appreciated in the non-inflamed areas. Here the lining epithelium demonstrates:
1) an undulating surface,
2) a very uniform thickness of about 6 to 8 cell layers,
3) a uniform palisading basal cell layer,
4) a parakeratotic surface, and 5) the absence of rete pegs. The cellular features are very bland.

Discussion: Odontogenic keratocyst (OKC) is one type of a developmental odontogenic cyst. They occur twice as frequently in the mandible as in the maxilla, and have a predilection for the posterior portion of the jaw (specifically, the angle of the mandible and the 3rd molar region of either jaw). OKC may be associated with an unerupted tooth (like a dentigerous cyst), an erupted tooth (like a periapical cyst) or may arise from a non-tooth bearing area of the jaw.

The recognition of OKC is based on the light microscopic appearance of its epithelial lining as noted in the histologic description above. Unfortunately, these diagnostic features may be entirely obscured in the context of an inflammatory background. In these instances, a specific diagnosis of OKC may not be possible based solely on the histologic features, and the pathologist may have to settle for a less specific diagnosis of “inflamed odontogenic cyst”.

Distinction of OKC from other types of odontogenic cysts is important. It has a significant potential for destructive growth and recurrence. In fact, about 35% of OKCs recur in contrast to a recurrence rate of about 5% for other types of odontogenic cysts. Moreover, approximately 5% of OKCs are associated with the nevoid basal cell carcinoma syndrome. Thus, the diagnosis of OKC, particularly recurrent OKCs, should raise the possibility of this syndrome.