Osteoblastoma or osteosarcoma: a diagnostic dilemma

Clinical presentation

A 14-year-old male patient exhibited painless swelling in the right mandibular canine-premolar region, persisting for 3 months. Upon examination, a firm, nontender mass was observed in right mandible with mobile teeth. Cone beam computed tomography revealed a partially well-defined mixed radiopaque-radiolucent lesion extending from the distal aspect of #27 root to distal aspect of #29 root. The lesion involved the buccal and lingual cortices, extending from alveolar crest to the middle to apical thirds of the roots in the involved teeth. Divergent premolar roots, mild widened apical periodontal ligament (PDL) space of #27 and #28, disruption of the lingual cortical plate, prominent expansion on lingual mandible were also noted. Crestal bone growth at the coronal thirds lingually was evident, whereas the mental foramen appeared unaffected.

Differential Diagnosis

Clinically, provisional diagnosis of cemento-ossifying fibroma was considered. Radiographic differential diagnosis included cemento-ossifying fibroma, osteoblastoma, or osteosarcoma.

Diagnosis and Management

Histologic examination revealed atypical pleomorphic osteoblasts with abundant osteoid formation in a well-vascularized fibrous stroma. The lesional tissue appeared to fuse to or invade the normal bony trabeculae and there was no fibrous capsule separating the abnormal osteoblastic activity from the adjacent normal bone. A diagnosis of well-differentiated osteoblastic osteosarcoma was made based on histological features and radiographic findings, particularly widening of PDL space. The case was sent to MD Anderson for second opinion and was diagnosed as “atypical osteoblastic lesion, most consistent with osteoblastoma.” The patient was treated by right marginal mandibulectomy.

Conclusion

The observed characteristics of crestal bone growth, external root resorption, and widened PDL space in this case were indicative of a malignant process. Distinguishing between osteoblastoma and osteosarcoma can occasionally pose challenges for pathologists, highlighting the significance of radiographic findings and cone beam computed tomography imaging in assisting histological interpretation and establishing a definitive diagnosis.