Unmasking an Incidental Tenosynovial Giant Cell Tumor on Fluorodeoxyglucose Positron Emission Tomography / Computed Tomography in a Melanoma Patient

Abstract Introduction: Tenosynovial giant cell tumor (TGCT) is a benign, yet metabolically active tumor affecting the synovium, bursa, or tendon sheath. Aim: The purpose of the current case report is to evaluate the importance of fluorodeoxyglucose positron emission tomography / computed tomography in diagnosis of extra osseous soft tissue lesion. Case report: We present a 48-year-old male with malignant melanoma undergoing fluorodeoxyglucose positron emission tomography / computed tomography surveillance. A highly fluorodeoxyglucose-avid mass in the right foot raised concern for melanoma metastasis. However, biopsy revealed an unexpected diagnosis of TGCT. Conclusion: This case highlights the importance of fluorodeoxyglucose positron emission tomography / computed tomography in diagnosis of extra osseous lesions, particularly in cancer patients. In such scenarios, considering alternative diagnosis and pathohistological diagnosis confirmation become crucial to avoid misdiagnosis of metastases. Keywords: positron emission tomography / computed tomography, giant cell tumor, melanoma.