The tumor ( Images A & B) shows lobules of cells similar to basal cells with masses of small keratinocytes surrounded by larger, palisading cells (Image C) on the periphery of the lobules. These uniform tumor cells possess large, oval, elongated nuclei and scant, poorly defined cytoplasm. There are no intercellular bridges. The nuclear size is relatively uniform and identifiable mitoses (Image D) are normal, although variable. The surrounding myofibroblastic stroma (Image C) is arranged in parallel bundles. There are an abundance of keratotic cysts and occasional retraction lacunae (Image C) where the stroma retracts from the tumor.
The odontogenic keratocyst is lined by a two to five layer squamous cell epithelium with a well-differentiated basal layer. It forms keratin, possesses no granulocytic cell layer or rete ridges, and may consist of one large cyst, or multiple microcysts.
The parakeratotic odontogenic cyst (Images E & F) possesses a thin lining of stratified squamous epithelium with a palisading basal layer and a corrugated surface of parakeratin. The epithelium surrounds a cyst cavity containing keratin.
The orthokeratotic odontogenic cyst (Image G) also possesses a thin surrounding epithelium but without a corrugated surface. There is a well-developed granular layer and a flattened or cuboidal, non-palisading, basal layer. This cyst cystcontains orthokeratin.