The added diagnostic value of complementary gadoxetic acid-enhanced MRI to (18)F-DOPA-PET/CT for liver staging in medullary thyroid carcinoma

BACKGROUND: A high proportion of patients with advanced stages of medullary thyroid carcinoma (MTC) present with liver metastasis metastases. The aim of our study was to investigate the added diagnostic value of complementary gadoxetic acid-enhanced MRI to (18)F-DOPA-PET/CT for liver staging in MTC. METHODS: Thirty-six patients (14 female, median age 55 years) with histologically confirmed MTC undergoing gadoxetic acid-enhanced liver MRI within 1 month of matching contrast-enhanced (18)F-DOPA-PET/CT between 2010 and 2016 were selected for this IRB-approved retrospective study. (18)F-DOPA-PET/CT and multiparametric MRI data sets were read consecutively and liver lesions were categorised on a 5-point Likert scale (1–definitely benign; 2–probably benign; 3–intermediate risk for metastasis; 4–probably metastasis; 5–definitely metastasis). It was noted if gadoxetic acid-enhanced MRI detected additional, (18)F-DOPA-PET/CT-occult metastases (category 5) or if gadoxetic acid-enhanced MRI allowed for a definite classification (categories 1 and 5) of lesions for which (18)F-DOPA-PET/CT remained inconclusive (categories 2–4). Follow-up PET/CT and MRI examinations were used as a reference standard. RESULTS: A total of 207 liver lesions ((18)F-DOPA-PET/CT 149, MRI 207; 152 metastases, 37 benign cysts, 18 hemangiomas) were analysed. Fifty-eight additional lesions were detected by MRI, of which 54 were metastases (median diameter 0.5 cm [interquartile range 0.4–0.7 cm]) occult on (18)F-DOPA-PET/CT. MRI allowed for a definite lesion classification (categories 1 and 5) in 92% (190/207) whereas (18)F-DOPA-PET/CT allowed for a definite lesion classification in 76% (113/149). MRI lead to a change in lesion categorisation in 14% (21/149). CONCLUSION: Gadoxetic acid-enhanced MRI allows for a more precise liver staging in MTC patients compared to (18)F-DOPA-PET/CT alone, particularly for (18)F-DOPA-negative metastases and lesions < 1 cm.