Benign Fibrous Histiocytoma of Bone

Storiform fibroblasts with osteoclast-type giant cells and foamy macrophages is the histology of a non-ossifying fibroma, but in this clinical setting - a painful pelvic lytic lesion in an adult - it represents benign fibrous histiocytoma of bone, which is histologically identical to a non-ossifying fibroma but is distinguished clinically by occurring in atypical locations, such as the pelvis, axial skeleton or long-bone diaphysis and epiphysis, and in older, symptomatic patients, in contrast to the young, asymptomatic, metaphyseal non-ossifying fibroma. It is a rare entity, less than one per cent of benign bone tumours, and somewhat controversial. Because the histology overlaps with several giant-cell-rich and fibrous lesions, the diagnosis is largely one of exclusion, so I would correlate the clinical picture, imaging - a well-defined lytic lesion, often with a sclerotic rim - and histology, ideally at a specialist bone-tumour centre, specifically to exclude giant cell tumour of bone, fibrous dysplasia, aneurysmal bone cyst and chondromyxoid fibroma. It is benign, and management is curettage with bone grafting, or simple resection, with grafting and fixation as needed for a structural lesion, which is usually curative. However, up to about eleven per cent recur, so I would follow the patient up, and I would be aware of the rare reports of malignant transformation. Finally, I would not confuse this benign entity with malignant fibrous histiocytoma, which is a different, malignant tumour now classified as undifferentiated pleomorphic sarcoma.