Ossifying fasciitis: A rare phenomenon and a mimicker for malignancy

Abstract

Abstract Introduction/Objective Ossifying fasciitis is a relatively rare variant of nodular fasciitis. However, it can mimic malignant lesions, particularly extraosseous osteosarcoma. The purpose of this report is to describe a florid case of ossifying fasciitis with an unusual clinical course in a 17-year-old male. Methods/Case Report A 17-year-old male underwent surgery at an outside hospital for a soft tissue mass in his left upper thigh that had been present for over two years. Pathology was consistent with a benign myofibroblastic tumor. No bone formation was present in the biopsy. Next generation sequencing showed a COL1A1::USP6 gene fusion. The patient was then referred to our institution due to rapid recurrence and unresolving infection at the surgery site. An ultrasound revealed a mass measuring 3.3 x 2.7 x 1.3 cm at the surgery site. The patient subsequently underwent wide surgical resection of the mass.Gross inspection and sectioning of the specimen revealed a well-defined, encapsulated firm calcified lesion with approximately 30% soft pink gelatinous cut surfaces. Microscopically, the lesion was composed of spindle-shaped fibroblastic cells and extensive osteoblastic activity with a zonated transition from immature osteoid to immature woven bone. The diagnosis of ossifying fasciitis was rendered. Results (if a Case Study enter NA) NA Conclusion Rapidly growing lesions can be misinterpreted as sarcomas. Careful microscopic examination and correlation with clinical and radiologic data is critical for accurate diagnosis. Molecular data can be helpful in difficult cases.