[Difficulties in the differential diagnosis of a non-traumatic, active myositis ossificans during pregnancy (author's transl)].

A 28 year old patient complained of sensory disturbances and pain in the right upper arm during pregnancy. During the 32nd week of her pregnancy, a large painful mass developed in the flexor muscles which, radiographically, showed some calcification. A diagnosis of a parosseous sarcoma was made; biopsy, however, indicated a diagnosis of non-traumatic myositis ossificans. Since the histological appearances of active myositis may be vary difficult to distinguish from a juxtacortical sarcoma, a right brachial angiogram and scintiscan were obtained. The angiographic and scintigraphic findings were erroneously considered to suggest malignancy. Following delivery, the tumour was removed. Futher histology confirmed the diagnosis of localised, non-traumatic myositis ossificans. The value of radiology, biopsy, angiography and scintigraphy are discussed with reference to our experience.