Background: Myositis ossificans (MO) is a rare non-neoplastic heterotopic ossification of soft tissue. Histological examination is the gold standard method for diagnosis, but fine needle aspiration (FNA) cytology may aid in presumptive diagnosis of this lesion. Cases: Nine patients with chief complaint of soft tissue mass with clinically suspected MO were selected. FNA of the mass showed low to hypercellular smears, composed of some amorphous pink to bluish material on Wright-Giemsa stain. The predominant cells were oval to spindle-shaped, resembling fibroblasts. Some cells had a high nucleo-cytoplasmic ratio with hyperchromatic nuclei, an irregular nuclear border and prominent nucleoli. Bland-looking osteoblasts and uni- and binucleated chondrocytes were also noted. FNA diagnosis of 4 patients was suggestive of osteosarcoma and of 2 patients suggestive of chondrosarcoma, 2 patients were diagnosed with a benign process and 1 was deferred due to hypocellularity of the smears. Histological examination of the corresponding surgical specimen confirmed the diagnosis of MO. Conclusion: MO cannot be diagnosed on FNA smears without analyzing the clinical and radiological findings. Experience shows that otherwise MO is mostly misdiagnosed as a malignant lesion.

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