MR imaging of myositis ossificans: variable patterns at different stages

Area of Science:

• Radiology
• Orthopedic Imaging
• Musculoskeletal Imaging

Background:

• Myositis ossificans (MO) is a benign condition characterized by heterotopic bone formation in muscle.
• Palpable masses can present diagnostic challenges, necessitating advanced imaging techniques.

Purpose of the Study:

• To evaluate the magnetic resonance (MR) imaging features of myositis ossificans (MO) at different stages of maturation.
• To assess the diagnostic utility of MR imaging, particularly with contrast enhancement, in differentiating MO from other soft tissue masses.

Main Methods:

• Retrospective review of five patients diagnosed with myositis ossificans (MO).
• Analysis of magnetic resonance (MR) imaging characteristics, including pre- and post-gadolinium contrast administration.
• Correlation of MR imaging findings with plain radiographs and histologic examination in excised lesions.

Main Results:

• MR imaging findings varied with MO maturation: early-stage lesions showed intermediate T1 signal, rim enhancement, and high T2 signal, mimicking inflammatory or neoplastic processes.
• Intermediate-stage MO exhibited fatty changes, while mature lesions displayed peripheral calcification.
• Histopathology confirmed osteoid production within spindle cell stroma.
• Postcontrast T1-weighted images revealed enhancement in adjacent muscles in some cases.

Conclusions:

• Magnetic resonance (MR) imaging features of myositis ossificans (MO) are nonspecific, especially in early stages, often mimicking inflammatory masses or neoplasms.
• The appearance of MO on MR imaging evolves with maturation, showing distinct patterns related to calcification and tissue composition.
• Correlation with clinical presentation, plain radiographs, and potentially biopsy is crucial for accurate diagnosis.