Focal liver uptake on FDG PET/CT without CT correlate: Utility of MRI in the evaluation of patients with known malignancy

OBJECTIVE. The purpose of this study was to determine the significance and utility of MRI in evaluation of focal hepatic uptake on FDG PET/CT without a CT correlate in patients with known malignancy. MATERIALS AND METHODS. In this retrospective study, we identified 36 of 1851 patients between 2005 and 2012 with known malignancy (19 women, 17 men; mean age, 56.1 years old) who had focal hepatic uptake on FDG PET/CT without a CT correlate and follow-up MRI within 100 days for assessment of uptake. Two radiologists reviewed the FDG PET/CT images together, reached consensus about presence of focal hepatic uptake, and measured maximum standardized uptake value (SUV_max) of the focal uptake and background liver. MR images were then reviewed to identify any correlate. Follow-up imaging and histopathologic data were reviewed to confirm or refute metastasis. Statistical correlation between intensity of FDG uptake and presence of focal lesions on MRI was performed. RESULTS. Fifty sites of focal hepatic uptake without CT correlate were identified. The median SUV_max was 4.1 (range, 2.1–10.1), whereas the ratio of median SUV_max of the hepatic lesion to that of normal parenchyma was 1.3 (range, 0.98–2.6). MRI confirmed focal lesions in 26 of 50 sites (52%). Seventy-seven percent of cases of hepatic uptake with an MRI correlate (20/26) were confirmed as metastatic disease (six cases at histopathology). Therefore, 40% of cases of hepatic uptake without a CT correlate (20/50) were metastases. We found no statistically significant difference in the SUV_max of hepatic lesions and SUV_max ratio between the groups with and without an MRI correlate (median SUV_max = 3.85 vs 4.2, p = 0.5; SUV_max ratio = 1.32 vs 1.31, p = 0.97) as well as between the groups with the final diagnosis of benign lesions and metastasis (SUV_max = 4.05 vs 3.95, p = 0.64; SUV_max ratio = 1.31 vs 1.32, p = 0.91). CONCLUSION.