Definition: Ameloblastoma is a neoplasm that recapitulates ameloblastic development. Ameloblastoma is essentially a locally aggressive epithelial neoplasm with features of the enamel organ.
Ameloblastomas occur in middle aged adults and have characteristic expansile mass with smooth, evenly rounded, multilocular radiolucency with scalloped borders. The cortex is thinned and may be penetrated.
There are three clinical types, solid ameloblastoma, unicystic ameloblastoma and peripheral ameloblastoma. Solid ameloblastoma involves the mandible in 80% of cases and the maxilla in 20%. The male:female incidence is equal and the median age is 35.
Radiographically the lesion may be unilocular or multilocular and the appearance has been described as being soap bubble or honeycomb like.
Ameloblastoma infiltrates cancellous bone such that a 1 centimeter margin beyond the radiographic extent of the tumor is suggested for surgical therapy.
Macroscopically, the cut surface is often cystic.
Microscopy
There are many islands of epithelial cells with steallate stromal cells surrounded by a peripheral rim of columnar or cuboidal epithelium that resemble the enamel organ. Strongly eosinophilic, PAS(+), degenerative substances are often seen at the center of the epithelial islands. Calcifications are not uncommon.
The follicular pattern characterized by discret islands of follicles of the aforementioned epithelial island or the plexiform pattern characterized by continuous anastomosing strands of the neoplastic epithelium are present. Other pattern including the unicystic, acanthomatous (with squamous cell metaplasia), granular cell type, desmoplastic, basaloid pattern, papilliferous and keratoameloblastoma.
Microcyst formation is frequent and they may coalesce to form large cysts. Granular cells, which occur singly or in large masses within the follicles, replace in whole or part of the stellate reticulum may be found.
The cytoplasmic granules are PAS(+). There may be substantial squamous metaplasia to suggest squamous cell carcinoma. In some cases, the vasculature is exuberant and may mimic hemangiomas.
Variants
Variants
There are many variants of solid ameloblastoma: follicular, acanthomatous, desmoplastic, basal cell, plexiform and granular cell.
Follicular variants are the most common and show epithelial islands with peripheral columnar cells with reverse polarity and whose central areas resemble stellate reticulum. Cyst formation is common and the stroma may be fibrous.
The acanthomatous variant shows abundant keratin formation and should not be mistaken for squamous cell carcinoma.
The desmoplastic variant shows small epithelial nests and cords with dense fibrous stroma. There are few peripheral palisaded cells and the centrally placed cells are less spindled.
The basal cell variant is least common and peripheral columnar cells can be lacking and there may be little stellate reticulum present.
The plexiform variant shows long anastomosing plexiform epithelial cords.
The granular cell variant shows cells whose cytoplasm is granular and the change may be focal or widespread. No matter what the variant, the behavior is the same.
Differential diagnosis
- ameloblastic fibroma and ameloblastomas share the same predilection of the molar ramus of the mandible. Often, but not always, they are associated with an unerupted third molar.
See also
Credits
USCAP 2005