Purpose: Because calcitonin level remains elevated after initial treatment in many medullary thyroid carcinoma (MTC) patients without evidence of disease in the usual imaging work-up, there is a need to define optimal imaging procedures.

Patients and methods: Fifty-five consecutive elevated calcitonin level MTC patients were enrolled to undergo neck and abdomen ultrasonography (US); neck, chest and abdomen spiral CT; liver and whole body MRI, bone scintigraphy and FDG PET/CT scan (PET).

Results: 50 patients underwent neck US, CT and PET and neck recurrence was demonstrated in 56%, 42% and 32%, respectively. Lung and mediastinum lymph node metastases in the 55 patients were demonstrated in 35% and 31% by CT and in 15% and 20% by PET. Liver imaging with MRI, CT, US, and PET in 41 patients showed liver in 49%, 44%, 41%, and 27% patients, respectively. Bone metastases in 55 patients were demonstrated in 35% by PET, in 40% by bone scintigraphy and in 40% by MRI; bone scintigraphy was complementary with MRI for axial lesions but superior for the detection of peripheral lesions. Ten patients had no imaged tumor site despite elevated calcitonin level (median: 196 pg/ml; range: 39–816). FDG uptake in neoplastic foci was higher in progressive patients but with a considerable overlap with stable ones.

Conclusion: The most efficient imaging work-up for depicting MTC tumor sites would consist of a neck US, chest CT, liver MRI, bone scintigraphy and axial skeleton MRI. FDG PET scan appeared to be less sensitive, and of low prognostic value.