Paediatric Imaging

Fatty liver

excess accumulation of fat within hepatocytes due to a variety of underlying causes. The commonest cause is exogenous steroid therapy, though children with Cushing disease may also develop a fatty liver. Familial hyperlipidaemia, malnutrition and cystic fibrosis are all recognised causes. There are no specific clinical findings though non-specific hepatic enlargement may be present.

Fatty infiltration is usually diffuse but on occasions may be focal and well defined. Sonography demonstrates diffuse increased parenchymal echogenicity with progressive loss of clarity of portal vein walls and increased attenuation of sound by the liver. In rare cases focal increased echogenicity is present, often in a geographic fashion with well defined margins. There is no displacement or compression of normal structures such as portal and hepatic veins.

Unenhanced computed tomography will show generalized or focal reduction in attenuation of liver parenchyma with no distortion of underlying vessels. Unenhanced portal and hepatic veins may have greater attenuation than surrounding parenchyma and so may 'stand out' in a similar fashion to enhancing vessels in a normal liver. Comparison of hepatic attenuation with that of splenic parenchyma is useful. Signal intensity of the liver on MR imaging will be skewed in the direction of fat and so will be increased on both T1- and T2-weighted spin-echo sequences, though the internal standard of the spleen will not be available, making subtle changes difficult to detect. Any increase in signal should not be present on fat-suppressed sequences such as STIR.

DG