Focal Nodular Hyperplasia of the Liver

Radiologic-Pathologic Correlation

Abstract Introduction Clinical Features

Pathologic Features Radiologic Features Differential Diagnosis Treatment And Prognosis

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Differential Diagnosis

The differential diagnosis of FNH includes vascular "scar" tumors of the liver: fibrolamellar carcinoma, hepatocellular adenoma, hepatocellular carcinoma, intrahepatic cholangiocar-cinoma, giant hemangioma, and hypervas-cular metastasis. Unfortunately, there may be enough overlap among the imaging features of these lesions and those of FNH to make distinction difficult or impossible in individual cases.

Fibrolamellar carcinoma is a malignant neoplasm of hepatocellular origin that is characterized by hepatocytes with eosinophilic cytoplasm and bands of lamellar fibrosis. This tumor may also contain a central scar, but a fundamental difference between this lesion and FNH is that fibrolamellar carcinoma is a malignant lesion and may demonstrate signs of malignancy including metastatic foci and retroperitoneal adenopathy. In addition, calcification, including central scar calcification, may be seen in up to 55% of cases, and the lesion is prone to internal hemorrhage and necrosis, features not seen in FNH (35,36,37) (Figure 12, Figure 13). It is, therefore, the homogeneous fibrolamellar carcinoma without a calcified central scar or evidence of metastasis that would be difficult to differentiate from FNH. In this scenario, MR imaging may be helpful; on T2-weighted images, the central scar in fibrolamellar carcinoma usually has low signal intensity, in contrast to the high-signal-intensity scar expected in FNH (29,35) (Figure 13). However, a high-signal-intensity central scar on T2-weighted images has been reported in cases of fibrolamellar carcinoma as well (38).

Hepatocellular adenoma represents a proliferation of normal-appearing hepatocytes and abnormal architecture lacking normal portal triads and central veins. Because it is a neoplasm (with unlimited growth capacity), hepatocellular adenoma tends to become larger (approximately 10 cm in average diameter) than FNH and has a propensity to hemorrhage, a feature that usually brings it to clinical and radiologic attention (Figure 14, Figure 15). Hepatocellular adenoma does not typically demonstrate a central scar.

Well-differentiated hepatocellular carcinomas may demonstrate an enhancement profile similar to that of FNH. Similar to fibrolamellar carcinoma, hepatocellular carcinomas are more prone to internal necrosis and hemorrhage than FNH and may demonstrate malignant features such as vascular invasion, metastatic disease, and adenopathy (Figure 16). During the enhancement phase of CT and MR imaging, a peripheral capsule may be seen on delayed images. This finding was originally thought to be helpful in distinguishing hepatocellular carcinoma from FNH (27,32), but rim enhancement of the pseudocapsule has been seen in FNH as well (30).

Intrahepatic cholangiocarcinomas are typically less hypervascular than FNH on CT scans obtained during the arterial phase and demonstrate more marked hypoattenuation during the portal venous phase of contrast enhancement. They may, however, demonstrate a dominant, usually large, central scar due to the desmoplastic nature of the tumor. In those cases of intrahepatic cholangiocarcinoma with a small scar, however, the lesion may be confused with FNH, particularly if the finding is observed on delayed contrast-enhanced CT scans (Figure 17). As in cases of fibrolamellar carcinoma and hepatocellular carcinoma, malignant features, when present, will be helpful in the differential diagnosis.

Giant hemangiomas (ie, those greater than 5-10 cm in diameter) frequently demonstrate a central scar due to areas of sclerosis and fibrosis, but these lesions are larger than the typical FNH. Calcification may be seen (<10% of cases), which would also allow it to be differentiated from FNH. The classic CT and MR imaging characteristics of hemangioma, which include globular, predominantly peripheral enhancement in the early arterial and portal ve- nous phases, followed by centripetal filling in and retention of contrast material on delayed images, are quite different from those of FNH (Figure 18). The characteristic signal intensity of an hemangioma, similar to that of cerebrospinal fluid on heavily T2-weighted MR images, would further differentiate it from FNH, despite the presence of a central scar (Figure 19).

A solitary hypervascular metastasis would also be capable of mimicking the imaging features of FNH. Most metastases, however, are usually hypovascular on CT scans obtained during the portal venous phase of enhancement, are associated with a known malignant neoplasm, occur in older patients, are multiple, and do not demonstrate central scars.

Abstract Introduction Clinical Features

Pathologic Features Radiologic Features Differential Diagnosis Treatment And Prognosis

Summary Source Information References