This tumor occurs most frequently in the posterior mandible, and usually appears as a well-demarcated unilocular or multilocular radiolucent lesion that can be associated with a crown of a nonerupted tooth. The neoplasm extends through cancellous bone, but usually is confined by compact bone such as the inferior border and ascending ramus of the mandible. These sites seem to act as effective barriers that prevent the tumor from spreading for some time.²

Histopathologically, ameloblastomas exhibit proliferating odontogenic epithelium within a background of fibrous stroma. The epithelium is characterized by prominent palisading of the basal cell nuclei (that is, reverse polarization) and by vacuolization of the cytoplasm of the basal cells. Within the epithelial islands, stellate reticulumlike areas may be noted. Foci of squamouslike changes, granular cells, clear cells and basaloid cells, as well as follicular, cystic and plexiform patterns, give rise to the histologic variants of this lesion.

Some of the variations in histologic patterns appear not to have significant bearing on prognosis. However, the unicystic variant appears to behave in a less aggressive manner. In 1984, Eversole and colleagues³ described the desmoplastic variant as an unusual type of ameloblastoma with special histologic and radiographic features. We describe two patients with this variant of ameloblastoma and analyze the literature to better understand this lesion.

	CASE REPORTS

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Case 1. A 52-year-old man with a 10-year history of diagnosed but untreated ameloblastoma visited one of us (S.M.) because of a hard painless swelling in the left maxilla. The patient’s medical history was unremarkable except for hypertension that was controlled with medication (5 milligrams of amlodipine with 20 mg of benazepril, one capsule in the morning).

An intraoral examination revealed a swelling covered by red, irregularly surfaced mucosa that extended from the molar region to the incisor region. The teeth were vital and exhibited slight mobility. Panoramic radiography revealed a mixed, diffuse, expansile lesion with involvement of the lamina dura and periodontal spaces. Computed tomography showed a high- and low-density (mixed) undefined lesion crossing the midline anteriorly and extending to the left maxillary molar area (Figure 1). In the axial view, the oral and maxillofacial surgeon found evidence of cortical destruction of the buccal plate with some degree of buccolingual expansion. The lesion also invaded the maxillary sinus in the coronal views.

View larger version (93K): [in this window] [in a new window]   Figure 1. Case 1: high- and low-density undefined lesion crossing the midline anteriorly.

View larger version (105K): [in this window] [in a new window]   Figure 2. Case 1: histologic section showing ameloblastic epithelial component surrounded by desmoplastic tissue (hematoxylineosin stain, x40).

Case 2. A 51-year-old woman visited one of us (S.M.) for evaluation and treatment of an expansile lesion of the anterior mandible that extended from the right canine to the left premolar area. The lesion had been present for two years. The patient’s medical history was significant for hysterectomy six years earlier.

The physical examination revealed a woman whose facial asymmetry was evident. The patient reported a history of a slowly enlarging anterior mandibular mass, but denied experiencing bleeding, pain or sensory changes.

The intraoral examination disclosed a large, hard, nontender mass of the anterior mandible, covered by a red, nonulcerated, unfixed mucosa. The lesion extended from the premolar region on the left side to the canine region on the right side. No lymphadenopathies or fistulae were present. The involved teeth were vital and slightly displaced lingually.

Panoramic radiography showed a mixed, expansile, diffuse lesion of the mandible (Figure 3). The computed tomographic scan revealed involvement of the buccal and lingual plates (Figure 4). The inferior cortical bone was intact, with no evidence of destruction or expansion. The differential diagnosis included a benign fibro-osseous lesion, a malignant bone tumor and an odontogenic tumor.

View larger version (97K): [in this window] [in a new window]   Figure 3. Case 2: panoramic radiograph shows expansile, radiopaque/radiolucent lesion with diffuse borders, as well as displacement of the teeth.

View larger version (47K): [in this window] [in a new window]   Figure 4. Case 2: computed tomographic scan of the mandible shows mixed expansile lesion with destruction of the cortical plates.

Two weeks after the biopsy, the surgeon performed a block resection, leaving the inferior border intact. He then immediately placed a posterior iliac crest bone graft. The patient’s postoperative course was uneventful. Postoperative radiography and a clinical follow-up examination one year later disclosed no recurrence or residual tumor.

	DISCUSSION

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Desmoplastic ameloblastoma exhibits important differences in anatomical distribution, histologic appearance and radiographic findings compared with other types of ameloblastoma. However, age and sex distributions do not differ from those seen in patients with other types of ameloblastoma.

Approximately half of the desmoplastic lesions are located in the maxilla, and the vast majority of them occur in the anterior or premolar portion of the jaws. This is in contrast to the location of the unicystic or classic types of ameloblastoma, which usually are found in the posterior area of the mandible. Maxillary lesions are more insidious than mandibular tumors owing to the proximity of vital structures and the maxillary sinus. Also, the very thin cortical bone of the maxilla forms a weak barrier for the spread of tumors. Consequently, maxillary ameloblastomas may be able to spread earlier and more quickly than do mandibular neoplasms.

The radiographic appearance of this neoplasm usually indicates a mixed radiolucent/radiopaque lesion. Approximately half of these lesions have diffuse borders in the radiograph⁴ and look similar to a fibro-osseous lesion or malignant tumor. The lamina dura also is involved.⁵ The radiographic appearance may indicate that this tumor is more aggressive than other variants of ameloblastoma.

Waldron and El Mofty⁶ described the histologic appearance of desmoplastic ameloblastoma as small ovoid islands and narrow cords of odontogenic epithelium widely separated by dense, moderately cellular, fibrous, connective tissue. Columnar cells with reverse polarity within the epithelial islands are present, but are not the dominant feature.

Spicules of mature lamellar bone trabeculae have been reported in intimate contact with the tumor, and invasion has been demonstrated.⁶ This histologic finding may indicate the potential for local invasion, and accounts for the diffuse radiographic imaging.

Desmoplastic ameloblastoma may exhibit a more aggressive behavior than do other types of ameloblastoma. Various facts about this lesion may suggest aggressiveness:

– a potential to grow to a large size⁶;

– the common location in the maxilla that may produce an early invasion of adjacent structures;

– the diffuse radiographic appearance and the histologic finding of bone invasion.⁶

Finally, it is almost impossible to find the exact interface of the lesion with normal bone, making it especially difficult to treat surgically.⁷

	CONCLUSION

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We have described two patients with the desmoplastic variant of ameloblastoma localized in the anterior portion of the jaw. In both cases, block excision was performed. Follow-up examination one and two years later revealed no recurrence of tumor.

The biological behavior of desmoplastic ameloblastoma is still not fully understood. This lesion will remain an enigma until researchers pursue more definitive tumor analysis techniques and aggressive follow-up and tracking in many more cases.