What are the common MRI features to determine if a focal hepatic lesion is hepatocellular or extrahepatocellular in origin?
Determination of the origin of a focal hepatic lesion as hepatocellular or extrahepatocellular is useful to establish a definitive diagnosis for the lesion. Commonly encountered lesions of hepatocellular origin include FNH, hepatic adenoma, focal hepatic steatosis, regenerative nodule, and HCC.
In general, lesions that are isointense to hyperintense in signal intensity relative to liver parenchyma on in-phase T1-weighted images are hepatocellular in origin, whereas lesions that are low in signal intensity relative to liver parenchyma are generally extrahepatocellular in origin. Presence of intralesional lipid content, as manifested by a loss of signal intensity within a hepatocellular origin hepatic lesion on out-of-phase T1-weighted images relative to in-phase T1-weighted images, is often seen in all of the hepatocellular origin hepatic lesions listed above except for FNH but is not seen in most extrahepatocellular origin hepatic lesions with the exception of lipid-containing hepatic metastases from clear cell renal cell carcinoma or adrenocortical carcinoma. Retention of hepatobiliary MRI contrast material within a lesion during the hepatobiliary phase of enhancement generally indicates presence of either focal hepatic steatosis, regenerative nodule, or FNH, whereas all other hepatic lesions appear hypointense relative to surrounding liver parenchyma during this phase of enhancement. Lesions with high T2-weighted signal intensity relative to liver but intermediate signal intensity relative to spleen tend to be due to a malignant neoplasm, whereas lesions with high T2-weighted signal intensity relative to both liver and spleen parenchyma are most often due to cysts or hemangiomas.