Intraosseous ameloblastoma with a prominent extraosseous component: pitfalls in diagnosis

Abstract

For many years, gingival tumors of what appear to be peripherally located intraosseous ameloblastoma (IA) arising from the alveolar bone surface have often been confused with peripheral ameloblastoma (PA) causing resorption of the underlying bone. We analyzed a series of five cases of ameloblastoma that demonstrated a combined PA and IA architecture. The tumor commonly involved the anterior-premolar area, mostly in the maxilla and mainly in middle-aged men. The clinical presentation was an exophytic gingival mass inferior to which was a small bone defect. The predominant extraosseous component showed a papillary gross surface, reflecting the histologic proof of fusion between the submucosal tumor and the surface epithelium. In addition to the PA-like growth pattern, common to all was the presence of neoplastic destruction of the alveolar process, corresponding to an associated radiolucent lesion. This restrained component was acceptable as IA. In two cases, recurrence was observed deep in the alveolar bone with no involvement of the gingiva. These tumors appear to be IA that arose from the marginal alveolar bone and grew preferentially in the gingiva, forming a PA-like appearance. From diagnostic, therapeutic and prognostic points of view, this type of IA should not be confused with PA.

Fig. 1

Case 3. a Pebbly surfaced mass, axial (b) and coronal (c) CT showing a pocket-shaped bone destruction, d gingival tumor showing multiple connections with the papillary surface epithelium and cupping of the underlying bone (H&E, ×6), e another area showing tumor growth far beyond the root tip (H&E, ×3), f deep-seated tumor nests (H&E, ×40), g isolated tumor follicle surrounded by the compact bone (H&E, ×100)

Fig. 2

Cases 1 (a–c) and 4 (d and e). a Radiographic cupping of the interradicular bone, b gingival tumor showing scattered nests just near the excision edge (H&E, ×8), c recurrence in the bone without involving the surface epithelium (H&E, ×20), d decalcified gross specimen showing tumor location (dottedline), e surface ulceration and resorption of the palatal alveolar process (H&E, ×3)

Fig. 3

Case 2. a Superficial bone defect with a small daughter radiolucency, b papillary gingival tumor showing a discrete nodule (H&E, ×6), c submucosal tumor nests fusing with the surface epithelium (H&E, ×100), d recurrent tumor deep in the alveolar bone (H&E, ×200)

Fig. 4

Case 5. a Exophytic nodular mass, b panoramic radiograph of bone destruction in the alveolar process, c T2-weighted MRI showing intraosseous tumor and mucosal cyst of the maxillary sinus (asterisk), d Scanning view of tumor and associated mucous retention cyst (asterisk) (H&E, ×3), e fusions of submucosal tumor with the gingival epithelium (H&E, ×40)

Fig. 5

Intraosseous ameloblastoma. A 52-year-old man presented with a 2-cm, firm mass on the left mandible, a interradicular radiolucency similar to Fig. 2a, b axial CT showing a thin but intact cortical bone, c and d whole tissue mount showing a peripheral rim of residual bone (H&E, c, ×3; d, ×40)