Focal Nodular Hyperplasia of Liver - CT and MRI

MRI of 30 year old female T1 weighted image showing well defined slightly hypointense lesion with central hypointense scar which is showing slightly hyperintense on T2 WI. In venous phase the lesion is showing homogeneous contrast enhancement (arrow). In delayed phase image there is enhancement of scar.

CT of another 28 year old female showing well defined showing arterial enhanging lesion in the left lobe of liver with central non enhancing scar. On venous phase image the lesion shows homogeneous contrast enhancement. In delayed phase image there is enhancement of scar.
Discussion:

FNH is considered a non-neoplastic, hyperplastic response to a congenital vascular malformation. Histologically, FNH is not a tumor and consists of benign-appearing hepatocytes occurring in a liver that is otherwise normal (i.e. no cirrhosis).
On CT scan the FNH are hypervascular lesions with homogeneous enhancement in arterial phase and hypodense central scars in arterial and venous phase, which enhance in the equilibrium phase. This is characteristic of FNH.
On MR typical FNH is slightly hypointense on T1WI and slightly hyperintense on T2WI. The scar is somewhat hyperintense on T2. The enhancement is as we expect with 'capillary blush' with a scar that enhances late in the equilibrium phase. We need to differentiate fibrolammellar carcinoma (FLC) of liver from FNH as the imaging findings are almost similar except for few differentiating points. The central scar is hyperintense on T2 in FNH where as it is Hypo in FLC. Scar enhances in delayed phase of contrast study in FNH where as it will not enhances in FLC. May see calcification in FLC and not in FNH.