Focal Liver Uptake on FDG PET/CT Without CT Correlate: Utility of MRI in the Evaluation of Patients With Known Malignancy.
retrospective_cohort · Level III
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- Also identified by DOI 10.2214/AJR.18.21035.
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Abstract
<b>OBJECTIVE.</b> 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. <b>MATERIALS AND METHODS.</b> 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<sub>max</sub>) 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. <b>RESULTS.</b> Fifty sites of focal hepatic uptake without CT correlate were identified. The median SUV<sub>max</sub> was 4.1 (range, 2.1-10.1), whereas the ratio of median SUV<sub>max</sub> 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<sub>max</sub> of hepatic lesions and SUV<sub>max</sub> ratio between the groups with and without an MRI correlate (median SUV<sub>max</sub> = 3.85 vs 4.2, <i>p</i> = 0.5; SUV<sub>max</sub> ratio = 1.32 vs 1.31, <i>p</i> = 0.97) as well as between the groups with the final diagnosis of benign lesions and metastasis (SUV<sub>max</sub> = 4.05 vs 3.95, <i>p</i> = 0.64; SUV<sub>max</sub> ratio = 1.31 vs 1.32, <i>p</i> = 0.91). <b>CONCLUSION.</b> More than half of the cases of focal hepatic uptake on PET/CT without a CT correlate had an MRI correlate in our study, and more than 75% of these lesions were metastases, regardless of SUV<sub>max</sub>.