Renal Metastasis and Dual ((18)F-Fluorodeoxyglucose and (131)I) Avid Skeletal Metastasis in a Patient with Papillary Thyroid Cancer

Differentiated thyroid carcinoma (DTC) though usually behaves in an indolent manner, can have unusual metastatic presentation. Initial presentation of metastatic disease has been reported in 1–12% of DTC being less frequent in papillary (~2%) than in follicular (~10%) thyroid carcinoma. Renal metastasis from DTC is very rare. To our knowledge, only about 30 cases have been reported in the English literature to date. To make clinicians aware that management of such high-risk thyroid cancer frequently requires novel multimodality imaging and therapeutic techniques. A 72-year-old female is described who presented with abdominal pain and bilateral lower limbs swelling. Initial contrast enhanced computed tomography (CT) scan of abdomen showed a well-encapsulated mass in the upper pole of right kidney favoring a renal cell carcinoma. Postright sided radical nephrectomy, histopathology, and immunohistochemistry reports suggested metastatic deposits from thyroid malignancy. (18)F-fluorodeoxyglucose (FDG) positron emission tomography-CT demonstrated hypermetabolic nodule in the left lobe of thyroid and a lytic lesion involving left acetabulum suggestive of skeletal metastasis. Subsequently, ultrasound-guided fine needle aspiration cytology of the thyroid nodules in bilateral lobes confirmed thyroid malignancy (Bethesda 6/6). Total thyroidectomy revealed papillary thyroid cancer (PTC) (follicular variant-PTC [FV-PTC]). After surgery, (131)I-whole body scan showed iodine avid lytic lesion in the left acetabulum. The present case is a rare scenario of a renal metastasis as the presenting feature of an FV-PTC. Dual avidity in metastatic thyroid cancers (iodine and FDG) is rare and based on the degree of dedifferentiation of the DTC.