Rapidly Resolving Myositis Ossificans in an Adolescent Female.

Myositis ossificans (MO) is a rare benign tumor characterized by heterotopic ossification of soft tissues. While the term "myositis" suggests that the lesion commonly affects muscles, it can also occur in rare locations such as tendons or subcutaneous tissues. MO is infrequent in children, primarily affecting young adults and adolescents. It presents distinct radiological and histological features. However, it is crucial to exclude malignancy when investigating heterotopic ossification. Surgical excision of the lesion following an appropriate biopsy is an option, but cases of self-limiting MO have been reported. We report a unique case of a 14-year-old girl who presented with painful restriction of movement in the lumbar and gluteal regions, without any history of trauma. The girl underwent thorough clinical and radiological investigations, with MRI revealing a circumscribed ossifying lesion measuring 3.8 × 2.3 cm in the gluteal subcutaneous area, lacking clear boundaries, with edema of the adjacent muscles. The lesion exhibited heterogeneous signal intensity and contrast enhancement, while 18F-FDG PET/CT revealed increased metabolic activity within the lesion. A US-guided needle biopsy was performed, confirming the diagnosis of MO with a typical zonal phenomenon. The girl was referred for surgical removal of the lesion within three months after the initial MRI. Upon re-evaluation, the mass was barely palpable, and subsequent MRI and CT scans showed a marked reduction in lesion size. We followed the patient, and in another three months, the mass had almost completely regressed. We aimed to report a unique case of an adolescent with an established diagnosis of MO, following appropriate radiological and histological evaluation. The rapid regression of the lesion suggests that MO can be managed conservatively in selected cases rather than through immediate surgery.