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Multiple hereditary exostosis (or diaphyseal aclasis) is a condition characterized by the development of multiple osteochondromas. The tendency for malignant transformation into chondrosarcoma is well known. Malignancy typically arises from the cartilaginous cap of the osteochondroma. Radiographs supplemented by computed tomography have an important role in the diagnosis of this condition. Magnetic resonance imaging shows the features of sarcomatous change and aids in differentiating malignancy from pseudotumours.

The classification of certain vascular bone tumors that show an epithelioid cytologic appearance remains confusing, with overlap in features of epithelioid hemangioma, hemangioendothelioma and epithelioid hemangioendothelioma. Radiographs of a 27-year-old woman who presented with ankle pain showed an expanded lytic-sclerotic lesion in the distal left fibula. Magnetic resonance imaging showed an intramedullary lesion with a small lateral intracortical component. The lesion was hypo- to isointense to muscle on T1-weighted images and heterogeneously hyperintense on T2-weighted images. Initial incisional biopsy was inconclusive. Open biopsy showed hemangioendothelioma with epithelioid morphology, and the lesion was completely resected with reconstruction using a peroneal fibular rotation graft. Examination of the resected specimen showed focal hemangioendothelioma with an epithelioid phenotype arising in a hemangioma. This case illustrates the difficulty and pitfalls of making the correct diagnosis on the basis of a small biopsy specimen.