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Eight cases are described of circumscribed heterotopic ossification in the soft tissues characterised by spontaneous onset, no history of trauma, and rapid course which have frequently led to a mistaken preoperative diagnosis of highly malignant tumour. The terminology differentiates it from myositis ossificans, which is a different entity. The authors emphasize the need for accurate evaluation of all the clinical and radiographic data in order to avoid an erroneous diagnosis of extraosseous osteogenic sarcoma or parosteal osteogenic sarcoma. In this regard, both radiography and histological examination demonstrate the so-called zoning pattern, namely a radiolucent central zone corresponding to the more immature area and consisting of fibrous tissue with active histiofibroblastic proliferations and a radiopaque peripheral area, where ossification is more mature the closer it gets to the periphery. Histological specimens obtained exclusively from the central area may lead even the most expert pathologists to a diagnosis of fibrosarcoma or osteogenic sarcoma. Finally, the pathogenetic aspects of the anomaly are discussed, as well as those concerned with the differential diagnosis from other types of heterotopic ossification.

115 cases of osteoid osteoma treated over more than 18 years is reported. In 1 case the nidus was manifested in 2 different sites after 14 years. The following is emphasized: the terminology for osteoid osteoma should be changed in reference to osteoblastoma; osteoid osteoma and osteoblastoma constitute different aspects of the same neoplasia; the number of observations of osteoid osteoma increases as there is greater knowledge on the varieties of the tumor; treatment, which is exclusively surgical, may be limited to excision of the nidus, in order to guarantee the best healing possible. Resection should be limited to observations where the nidus is masked by osteosclerosis.

Eleven cases of malignant fibrous histiocytoma of bone observed during recent years are reported. An analysis is presented with regard to sex, age, site, symptoms, radiography, macroscopic and microscopic aspects. The differential diagnosis is discussed on the basis of these criteria. Because of the small number of cases and limited follow up, it was not possible to come to any definite conclusions concerning prognosis and treatment. Treatment was surgical in almost all the cases.