Medullary Thyroid Carcinoma: Imaging

Imaging plays an important role in the early detection and staging of medullary thyroid carcinoma (MTC), as well as in follow-up to locate early recurrence. MTC is a rare, calcitonin-secreting thyroid malignancy that is often diagnosed by ultrasound and calcitonin screening as part of the routine evaluation of any thyroid nodule. If serum calcitonin is elevated, imaging studies are needed for preoperative staging to guide surgical management. This may include ultrasound of the neck and abdomen. CT or MRI studies for more distant disease are performed preoperatively when calcitonin levels are greater than 500 pg/mL. Neither FDG-PET/CT nor F-DOPA-PET/CT is routinely being used for preoperative staging, but may be helpful in individual cases of doubt. Postoperative elevated calcitonin is associated with persistence or recurrence of MTC. Imaging studies to localize tumor tissue in postoperative follow-up include ultrasound, CT, MRI, and PET scans. However, they should be used judiciously, as the impact of treatment is often limited. In addition, even patients with persistent disease may survive long enough to accumulate significant radiation doses from CT or PET scans. Imaging studies are also useful in diagnosing associated components of hereditary MTC, such as pheochromocytoma and primary hyperparathyroidism.