Highly cellular bone-forming neoplasm composed of sheets and nodules of large polygonal to epithelioid osteoblastic cells with abundant amphophilic to eosinophilic cytoplasm and vesicular nuclei with conspicuous nucleoli, associated with irregular seams of un-mineralized osteoid and short trabeculae of immature woven bone produced directly by the tumor cells within a variably loose, fibrovascular stroma containing prominent capillaries and scattered osteoclast-type multinucleated giant cells. The tumor demonstrates moderate nuclear pleomorphism with identifiable mitotic figures but no evidence of abnormal ones. There is nodular aggregates of the tumor cells extending into adjacent soft tissue. No definite chondroid matrix is present. Overall, the histomorphologic features are those of an aggressive osteoblastic neoplasm with extraosseous soft-tissue involvement.
Expansile lytic lesion at middle third of right clavicle with basilar calcification. ? Osteoblastoma.
Soft tissue and bone fragments collectively measured 11x8.5x2.5 cm, largest is 5.5x4.5x2.5 cm.
Rt clavicle lytic lesion, excision biopsy:
COMMENT: