Ossifying fasciitis of the hand: case report and review of diagnostic pitfalls.

Ossifying fasciitis represents an uncommon benign lesion within the spectrum of reactive fibroblastic proliferations. It is defined by the coexistence of spindle-cell proliferation and heterotopic bone formation, a combination that can easily simulate malignant soft-tissue tumors. Because of its rapid growth and radiologic density, it is frequently mistaken for sarcomatous processes. Although most cases occur in the trunk and proximal extremities, presentation within the hand is exceptionally rare. We describe a 34-year-old male who developed a painless nodule on the palmar aspect of the right hand growing over two months. Imaging revealed a well-circumscribed lesion with heterogeneous signal intensity adjacent to the flexor tendon. The excised mass was composed of fibroblasts and myofibroblasts arranged in fascicles within a fibromyxoid stroma, showing osteoid formation rimmed by osteoblasts and scattered multinucleated giant cells. No cytologic atypia or atypical mitoses were present. Immunohistochemistry demonstrated diffuse smooth-muscle-actin (SMA) positivity and absence of H-caldesmon and ALK expression, confirming a diagnosis of ossifying fasciitis. This case underscores the diagnostic pitfalls of ossifying fasciitis, particularly when arising in unusual anatomic locations. Awareness of its characteristic histologic features and correlation with clinical and imaging findings is crucial to avoid misinterpretation as a malignant neoplasm and to prevent unnecessary radical surgery. Reporting such cases expands understanding of their variable presentations and contributes to refining clinical decision-making.