18F-Fluoride Uptake in Soft Tissue Metastases of Medullary Thyroid Carcinoma as a Marker of Progressive Calcification.

F-fluoride (F-NaF) uptake in soft tissue metastases of medullary thyroid carcinoma (MTC) has been reported. However, the evolution of these metastatic sites has rarely been assessed. We present a case of F-NaF uptake in multiple liver metastases of MTC initially without macroscopic calcification. The CT follow-up studies showed a progressive calcium deposition in the lesions. Therefore, this case suggests that the F-NaF uptake in MTC metastases could potentially be a marker of an ongoing calcification process instead of an inert deposit of calcium.