Bilateral Renal Metastasis of Hürthle Cell Thyroid Cancer with Discordant Uptake Between I-131 Sodium Iodide and F-18 FDG.

Renal metastasis of thyroid cancer is extremely rare. We report the case of a 62-year-old woman with Hürthle cell thyroid cancer (HCTC) with lungs, bones, and bilateral kidneys metastases. The renal metastatic lesions were clearly demonstrated by ¹³¹ I whole body scan (WBS) with SPECT/CT. However, they exhibited false-negative results in ¹⁸ F-FDG PET/CT, kidney ultrasonography, and contrast-enhanced CT scan. The findings imply that tumors have low glucose metabolism and are able to accumulate radioiodine, which is not commonly found in the relatively aggressive nature of HCTC. The patient received two sessions of 200 mCi ¹³¹ I therapy within 6 months duration. There was complete treatment response as evaluated by the second post-therapeutic ¹³¹ I SPECT/CT and serum thyroglobulin. To our knowledge, renal metastasis from HCTC with positive ¹³¹ I but negative ¹⁸ F-FDG uptake has not been reported in the literature. This case suggests that ¹³¹ I SPECT/CT is useful for lesion localization and prediction of ¹³¹ I therapy response.