Page 886 - Textbook of Pathology, 6th Edition

870 muscles of the thigh of a horseman, or may be single injury Histologically, the central region of the mass shows
followed by haemorrhage into the muscle. The patient loosely-arranged fibroblasts having high mitotic activity.
generally complains of pain, tenderness and swelling. Towards the periphery, there is presence of osteoid matrix
Richly vascularised granulation tissue replaces the affected and formation of woven mineralised bone with trapped
muscle or tendon. Then follows development of osteoid skeletal muscle fibres and regenerating muscle (myogenic)
and bone at the periphery, giving characteristic X-ray giant cells. The appearance is sufficiently atypical to
appearance. suggest osteosarcoma but osteosarcoma lacks maturation
phenomena seen in myositis ossificans. This is why the
Grossly, the lesion appears as unencapsulated, gritty mass condition is also called pseudomalignant osseous tumour of
replacing the muscle.
the soft tissues.

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SECTION III

Systemic Pathology