Fine-needle aspiration biopsy cytology of myositis ossificans

Increased utilization of fine-needle aspiration cytology to better define mass lesions before surgical excision can occasionally expose a cytologically worrisome yet biologically benign proliferative process. Such a proliferation may mimic a malignant neoplasm but is actually benign. Because of its limited exposure in the literature, we describe the cytopathology of two cases of myositis ossificans obtained by the fine-needle aspiration biopsy technique. Both lesions occurred in adolescents. One involved the deep muscle of the thigh, whereas the other was a superficial lesion of the anterior abdominal subcutaneous fat. In both instances a benign entity was favored, but in one case sarcoma could not be absolutely excluded by fine-needle aspiration cytology. Follow-up surgical excision in one case, and incisional biopsy in the other confirmed the diagnosis of myositis ossificans (MO). The cytologic differential diagnosis of this lesion is discussed.