Aggressive osteoblastoma, left mandible, canine. The epithelioid component has cells with a variable amount of lightly eosinophilic to basophilic cytoplasm with discrete margins in some regions. Nuclei of vary in size, and are oval to irregular with fine chromatin and indistinct nucleoli. Very occasional normal mitotic figures are present. The tumor has undergone coagulation necrosis in a region at the periphery of the basal-most portion.
Tumor extends to the surgical margin.
The AFIP fascicle describes osteoma, osteoid osteoma and osteoblastoma. This tumor somewhat resembles a variant of osteoblastoma, the aggressive osteoblastoma. Cellular atypia and bony invasion were not present to suggest the osteoblastic variant of osteogenic sarcoma. Histologically the mass is very similar to the original biopsy. This unusual lesion was the subject of a lengthy discussion.