Chao Wang, Hong Li
Ossifying Fibromyxoid Tumor (OFMT) is a rare mesenchymal neoplasm of intermediate biological potential that typically presents as a slow-growing mass. We report a diagnostic challenge involving a 54-year-old male with a 20-year history of a thigh mass that recently exhibited rapid enlargement and ulceration. Initial superficial biopsy led to a high suspicion of cutaneous tuberculosis due to false-positive acid-fast bacilli (AFB) staining and a positive T-SPOT, despite negative tuberculosis serology and normal inflammatory markers. This diagnostic pitfall was attributed to the "shell" of superficial ossification, which caused sampling error and nonspecific dye retention mimicking mycobacteria. Computed tomography (CT) was pivotal in resolving this discrepancy by revealing a characteristic "core-shell" pattern-a well-defined soft tissue tumor core beneath a dense ossified layer. Following a multimodal diagnostic integration, the patient underwent wide local excision with a 2.0 cm margin and reconstruction via split-thickness skin grafting. Histopathology and immunohistochemistry, showing partial loss of INI-1 expression, confirmed the diagnosis of OFMT. No recurrence or metastasis was observed during a 2-year follow-up. This case underscores the necessity of imaging to bypass biopsy limitations imposed by superficial ossification and highlights the risk of inappropriate anti-tuberculosis therapy when microbiological morphology conflicts with the broader clinical and radiological picture.