ABSTRACT
BACKGROUND: A large painful mass on the posterior neck of a child of a relatively short duration is uncommon. Barring infectious origin, differential diagnosis can be difficult without a definitive biopsy. METHODS AND RESULTS: A 12-year-old girl had a markedly painful posterior neck mass and limitation of neck motion without fever for 1 month. The rapid clinical course and poorly defined marginal zone of the CT images led to suspicion of malignancy. Although the initial frozen section suggested low-grade fibrosarcoma, a successful wide excision and paraffin pathology confirmed the diagnosis of myositis ossificans circumscripta (MOC) from the semispinalis capitis muscle. CONCLUSION: The occurrence of MOC in children is rare and may easily be misdiagnosed as soft tissue sarcoma. Both knowledge of the disease and guidelines for taking an aggressive biopsy sample are essential for correct diagnosis and appropriate treatment.
