Fig 1. Algorithm for incidental liver lesions. If inadequate imaging is available to ascertain the presence of benign versus suspicious features in a >=1-cm lesion, prompt MRI is advised. Low-risk patient: no known primary malignancy, hepatic dysfunction, or hepatic risk factors (see Table 1). High-risk patient: known primary malignancy with a propensity to metastasize to the liver, cirrhosis, and/or other hepatic risk factors (see Table 1). Follow-up MRI in 3 to 6 months. May needmore immediate follow-up in some scenarios. CT is also acceptable in a patient with cancer who is due for routine CTsurveillance. Benign features: sharp margin, homogeneous low attenuation (=<20 Hounsfield units [HU]) on noncontrast and/or portal venous–phase imaging, and characteristic features of hemangiomas, focal nodular hyperplasia (FNH), focal fatty sparing or deposition, or perfusional changes (see “Commonly Encountered Benign Lesions” subsection). If pseudoenhancement is present, a benign cyst may measure >20 HU; radiologists’ discretion is necessary. Suspicious features: ill-definedmargins, heterogeneous density, mural thickening or nodularity, thick septa, and intermediate to high attenuation on portal venous–phase imaging (>20 HU, in the absence of pseudoenhancement). If pre- and postcontrast CT is available, enhancement >20 HU is a suspicious feature.To evaluate, prefer MRI. “Flash-filling” feature: uniform hyperenhancement relative to hepatic parenchyma on arterial phase (including late arterial/early portal venous–phase) postcontrast imaging. If additional postcontrast phases are available to characterize lesion as benign (eg, hemangioma) or suspicious (eg, hepatocellular carcinoma), the lesion should be placed in one of those respective categories and not here. 8Incidental hepatic lesions that are>1.5 cmand do not have benign features should at least undergo prompt MRI. Direct biopsy (without MRI) may be appropriate in some scenarios. Differentiation of FNH from adenoma is important, especially if larger than 3 cm and subcapsular in location; for such patients, MRI with gadoxetate disodium is advised. If biopsy is pursued, core biopsy is preferred over fine-needle aspiration.