The significance of lower extremity FDG PET/CT imaging in patients with unknown primary tumor

If a suspicious finding for primary site of an unknown primary tumor (UPT) is found in limited whole-body FDG PET/CT imaging area, imaging of lower extremities is generally not performed in routine practice. This approach may not be true. In this case, FDG PET/CT imaging was performed in patient with UPT. The limited whole-body FDG PET/CT images showed an increased FDG uptake in a thyroid nodule which was seemed to be a primary lesion at first sight. But similar FDG PET/CT findings might be observed in benign thyroid nodules. So we also acquired FDG PET/CT images of the lower extremities. Then, a mass showing increased FDG uptake was seen in the left thigh. On histopathologic examination, the thyroid nodule was found to be benign and the left thigh mass was diagnosed with a malignant (hemangiopericytoma). This case demonstrates contribution of lower extremity FDG PET/CT imaging to detection of primary site of UPTs in suspected situations.