Myositis ossificans and fibroosseous pseudotumor of digits: a clinicopathological review of 64 cases with emphasis on diagnostic pitfalls.

Myositis ossificans (MO) and fibroosseous pseudotumor of digits (FP) are pseudotumoral mimics of malignancy. A review of 50 cases of MO and 14 cases of FP showed that a malignant diagnosis was suggested by referring pathologists in 23% of MO and 9% of FP. The most common misdiagnosis was osteosarcoma. Awareness of the spectrum of clinicopathological features of MO and FP will help pathologists avoid misdiagnoses. A comparison of the clinicopathological features of MO and FP showed that most features were similar, but FP involved an older age group (p<0.001). MO showed a statistically significant higher tendency to contain fibrinous material (p=0.007), edematous lymphangioma-like areas (p=0.013), and cartilage (p=0.017) and FP to contain excessive immature osteoid (p=0.029). These differences may be related to the site of occurrence.