A Case of 18F-FDG PET/CT Imaging of Kidney Metastases in Papillary Thyroid Carcinoma

A 60-year-old male patient underwent a PET/CT scan at our hospital one month ago, which revealed a lesion in the right kidney. Four years ago, he had radical surgery for thyroid cancer and neck lymph node dissection at another hospital, with postoperative pathology confirming papillary thyroid carcinoma. Physical examination revealed no palpable masses in the bilateral renal regions, and no tenderness or percussion pain was detected. Laboratory tests indicated the patient had mild anemia and slight renal function abnormalities. CT scan showed a round isodense lesion in the upper pole of the right kidney, measuring approximately 1.8×1.3 cm, with mild to moderate enhancement on contrast scans, appearing to have ring-like enhancement; CT diagnosis: lesion in the upper pole of the right kidney, considering the medical history, metastatic tumor was suspected. The 18F-FDG PET/CT scan showed an isodense nodule in the upper pole of the right kidney, measuring approximately 2.4×1.5×1.8 cm, with increased FDG uptake, maximum SUV of 19.4; PET/CT diagnosis: isodense nodule in the right kidney with increased glucose metabolism, suggesting renal metastasis. After admission, the patient underwent a laparoscopic partial nephrectomy of the right kidney at our hospital. Postoperative pathology revealed tumor cells exhibiting a branching papillary pattern, rich in colloid tissue, abundant eosinophilic cytoplasm, variable nuclear size, irregular nuclear shape, and glassy degeneration, all of which are characteristics of metastatic papillary thyroid carcinoma. Based on the medical history, various clinical examination results, and postoperative pathology findings, the right kidney mass was ultimately diagnosed as a rare distant metastasis of papillary thyroid carcinoma—metastasis of papillary thyroid carcinoma to the right kidney.