Pediatric myositis ossificans mimicking osteosarcoma.

Area of Science:

• Orthopedics
• Pathology
• Radiology

Background:

• Myositis ossificans (MO) is a benign heterotopic bone formation typically seen in young adults post-trauma.
• Distinguishing MO from malignant bone tumors like osteosarcoma can be challenging.

Observation:

• An 11-year-old girl presented with a shoulder mass initially misdiagnosed as osteosarcoma.
• Radiographic and MRI findings included ill-defined densities, periosteal reaction, and inhomogeneous signals.
• The patient lacked a trauma history, adding diagnostic complexity.

Findings:

• Histological examination revealed a pseudosarcomatous appearance.
• The case highlights atypical radiographic features and site predilection for MO in a pediatric patient.
• Correct diagnosis was achieved through detailed pathological evaluation of different stages.

Implications:

• This case underscores the importance of considering MO in pediatric differential diagnoses, even with atypical presentations.
• Emphasizes the critical role of pathological assessment in differentiating benign from malignant bone lesions.
• Highlights challenges in diagnosing MO when typical risk factors like trauma are absent.