Utility of Magnetic Resonance Imaging in Evaluating Focal Hepatic Uptake on 18F-FDG PET/CT Without a Computed Tomography Correlate in Patients with Known Malignancy – A Single-Center Retrospective Study

Objectives: The aim of this study is to assess the utility of contrast-enhanced magnetic resonance imaging (MRI) of the liver in determining the presence or absence of hepatic metastatic disease in patients with known malignancy who had focal hepatic uptake without computed tomography (CT) correlate on 18fluorine-fludeoxyglucose–positron emission tomography/CT (FDG-PET/CT) examinations. Material and Methods: In this retrospective study, a review of all 18 FDG-PET/CT images acquired in the Royal Hospital between 2015 and 2021 of patients with a known malignancy who had focal hepatic uptake on PET/CT without CT correlate and consequently evaluated by liver MRI within 100 days. The observations were initially blindly assessed on 18 FDG PET/CT subjectively and with quantification methods using the maximum standardized uptake value (SUVmax) of the focal uptake as well as of the background liver. Thirty-six (18 females, 18 males; mean age = 51 years) patients were identified. Simultaneously, contrast-enhanced liver MRI examinations of the same population were blindly reviewed by a fellowship-trained body imaging radiologist, and the presence or absence of a metastatic or nonmetastatic lesion was determined. Finally, the findings were correlated with the histopathology diagnosis if available and/or with follow-up examinations to confirm the presence or absence of metastasis. Results: Fifty-seven observations of focal hepatic uptake without CT correlation were identified in the 36 subjects. Thirty-seven focal liver lesions out of 57 observations were confirmed by contrast-enhanced MRI as true findings. The median SUVmax for those observations was 5.0 (range = 2.7–16.2), whereas the ratio of the median SUVmax of the hepatic lesion to that of normal parenchyma was 1.8. Eighty-one percent of the cases of focal hepatic uptake with corresponding MRI findings were confirmed to be metastatic lesions by imaging. Seven cases out of 37 focal liver lesions were benign. There was no significant difference in the SUVmax of the hepatic lesions and SUVmax ratio between the groups with and without corresponding MRI findings (median SUV max = 4.3 vs. 5.0, SUVmax ratio = 1.8 vs. 1.4, P = 0.213, respectively). However, there was a significant difference in the SUVmax between the groups with the final diagnosis of benign lesions and metastasis (SUV max = 4.6 vs. 5.1, SUVmax ratio = 1.5 vs. 1.9, P = 0.016). Conclusion: More than half of the observations of focal liver uptake seen on PET/CT without a CT correlate had an MRI correlate in our study, and 81% of those lesions were diagnosed as metastases based on imaging and follow-up imaging features, with no significant statistical difference of the SUV max values.