Contributed by Jeremie Berdugo MD, Elizabeth Bilodeau DMD, MD, MsEd FINAL DIAGNOSIS
Primordial odontogenic tumor with hard tissue formation.
DISCUSSION
Primordial odontogenic tumor (POT) was recently included in the 4th Edition of the World Health Organization Classification of Head and Neck Tumours.(1) 13 cases have been reported in the English literature .2-8 The average age is 12 years old and there is a slight male predilection. POT typically occurs in the mandible and presents as a buccal or lingual swelling (2-8).
Radiographically, the tumor is usually associated with the crown of an unerupted tooth, and it expands the adjacent cortical bone (1-8). The main radiological differential diagnosis is dentigerous cyst, and no recurrence have been reported (1-8).
Grossly, POT is a white and solid mass (1-8). A thin membrane surrounding the nodule can be appreciated grossly (1-8). Histologically, there is a central dental papilla-like myxoid stroma with peripheral hypercellularity, surrounded by a cuboidal to columnar epithelium with reverse nuclear polarity, reminiscent of the internal enamel epithelium of the enamel organ (1-8). Stellate reticulum has been reported on the external aspect this epithelial lining (2,4, 5). In one case, tooth germ-like structures composed of a mesenchymal and epithelial component were present (7) This case possessed foci of enameloid material formation (7) A second case had foci of calcifications and had originally been diagnosed as an immature complex odontoma (8).
There is some controversy surrounding the nature of POT. It has been suggested that POT may not warrant the designation of a tumor, and it may represent a soft tissue odontoma (with a massively enlarged dental papilla), primitive ameloblastic fibroma, or primitive odontogenic fibroma (4, 9). Also, POT-like areas have been found in complex odontomas (4). Finally, like our POT, complex odontomas have been reported in association with macrodontia, which may be another argument in favor of POT being a developmental or malformative process (10).
Pathological differential diagnosis includes hyperplastic dental follicle, odontogenic myxoma, ameloblastic fibroma and complex odontoma (4). These lesions possess a stromal component surrounded by an epithelium with ameloblastic differentiation. Primordial odontogenic cyst or archegonous odontogenic cyst (AOC) is another cyst that contains a myxoid stroma with subepithelial hypercellularity (11). However, AOC is cystic and its epithelium does not exhibit reverse nuclear polarization (11). Finally, presence or absence of hard tissue is no longer helpful in distinguishing POT from AOC or complex odontoma (7, 9).
In our case, given hard tissue formation adjacent to the central epithelium, the diagnosis of ameloblastic fibro-odontoma was considered, but the majority of the lesion consisted of a primitive mesenchymal component entirely surrounded by an epithelium displaying reverse nuclear polarity. Thus, the tumor was diagnosed as a primordial odontogenic tumor with hard tissue formation. In conclusion, this is the first time that well developed and mineralized dental hard tissue is described in an otherwise typical POT.
REFERENCES
Contributed by Jeremie Berdugo MD, Elizabeth Bilodeau DMD, MD, MsEd
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