Focal nodular hyperplasia

Background

Focal nodular hyperplasia (FNH) is a benign hepatic tumor. It is the second most common liver tumor (after hemangioma). It is caused by a hyperplastic response to a localized vascular abnormality.

Imaging Findings

FNH may appear as a iso- or hypoattenuating lesion on noncontrast CT. It shows intense enhancement during arterial phase of contrast enhancement, but becomes iso- or hypoattenuating during the portal venous phase (Figure 1A). On delayed images, it becomes isoattenuating compared to liver with a hyperattenuating central scar.

T1-weighted images show an iso- to slightly hypointense mass with a hypointense central scar (Figure 1B). T2-weighted images show an iso- to slightly hyperintense mass with a hyperintense central scar and a hyperintense pseudocapsule (Figure 1C). Dynamic contrast-enhanced T1-weighted images show a homogeneous hyperintense mass and hypointense central scar during the arterial phase (Figure 1D) and an isointense mass during the portal venous phase (Figure 1E). Delayed images show an isointense mass with a hyperintense central scar, as well as enhancement of the pseudocapsule (Figure 1F).

The pseudocapsule is due to compression of liver parenchyma surrounding the FNH, vessels surrounding FNH, as well as inflammation.

On F18-FDG PET, FNH typically has uptake similar to or lower than adjacent liver.

Differential diagnosis

• Hepatic adenoma
• Fibrolamellar heptaocellular carcinoma: Has a fibrous scar that is hypointense on T2-weighted images. Enhancement typically heterogeneous.
• Hepatocellular carcinoma (HCC): A tumor capsule (as opposed to a pseudocapsule) may be seen in HCC and is hypointense on T1- and T2-weighted images and it demonstrates enhancement on delayed images.
• Small cavernous hemangioma