A Case Report of Diffuse-type Tenosynovial Giant Cell Tumor as a Calcaneus Mass: A Diagnostic Challenge

Introduction Diffuse-type tenosynovial giant cell tumor (D-TGCT) originates from synovial cells in tendon sheaths and bursae and rarely presents as a calcaneal mass.Case Report A 44-year-old female presented with left heel pain that had persisted for over a year and had worsened over the past six months. A mass was found on the Lateral radiograph of the calcaneus, which was diagnosed as an aneurysmal bone cyst. Non-contrast computed tomography (CT) and magnetic resonance imaging (MRI)diagnosed a benign tumor. Based on light microscopy, special stains, and immunohistochemistry, a final diagnosis of diffuse tenosynovial giant cell tumor (D-TGCT) was rendered.Results D-TGCT is a slow-growing, infiltrative tumor that can form single or multiple masses outside the joint, and can also involve adjacent jointsmainly affects weight-bearing joints such as the knee, hip, and ankle. However, D-TGCT presents as a calcaneal mass, which poses a diagnostic challenge for all radiologists.Conclusion A calcaneal mass exhibiting well-defined borders, focal cortical destruction, a sclerotic rim, and T2WI hypointensity, the possibility of D-TGCT should be considered.