Benign liver tumors in pediatric patients - Review with emphasis on imaging features

Table 1 Imaging features

US	Computed tomography	Magnetic resonance imaging
Infantile hepatic hemangioendothelioma
2D	Pre-contrast examination	T1-weighted images
Hypoechoic1	Hypodense1, well-defined	Hypointense1
Doppler US	Post-contrast examination	± hyperintense foci2
Enlarged hepatic arteries and veins, shunts	Intense, homogeneous enhancement3/peripheral enhancement4 with progressive centripetal filling-in pattern	T2-weighted images
CEUS		Hyperintense
Peripheral enhancement, with centripetal filling-in		Enhancement pattern
		Centripetal filling-in
Mesenchymal hamartoma
2D	Cystic components	Cystic components
Cystic and solid5 components in various amounts6	Water attenuation	T1-weighted images
Thin/thick and mobile septa	Non-enhancement	Variable signal intensity on (depending on the protein content)
Parietal nodules
Rare features7		T2-weighted images
		High signal intensity
Doppler US	Solid components	Solid components
Linear blood flow within solid portions and septa	Hypodense	Hypointense on both T1- and T2-weighted images (fibrosis)
Surrounding portal and hepatic veins may be displaced	Post-contrast enhancement
CEUS		Post-contrast mild enhancement (and within the septa)
Solid component may present arterial and portal venous enhancement
Focal nodular hyperplasia
2D	Pre-contrast examination	T1-weighted images
Well-circumscribed	Isodense/slightly hypodense	Isointense/slightly hypointense to the liver
Variable echogenicity	Hypoattenuating central scar	Hypointense central scar
Stellate hyperechoic central scar	Arterial and early portal phases	T2-weighted images
Doppler US	Homogeneous enhancement, earlier and more intense than the surrounding liver parenchyma	Isointense/slightly hyperintense
Spoke-wheel pattern	Hypoattenuating central scar	Hyperintense central scar
CEUS	Late portal and delayed phases	Arterial phase
Arterial and portal venous enhancement	Isoattenuating to the liver	Hyperintense lesion
	Delayed enhancement of the central scar	Non-enhanced central scar
		Portal venous phase
		Slightly hyperintense/isointense
		Delayed phase
		Enhancement of the central scar
Nodular regenerative hyperplasia
2D	Pre-contrast examination	T1-weighted images
Multiple, tiny, well-circumscribed, hypo-/isoechoic nodules8	Hypo-9/isoattenuating to the liver	Slightly hyperintense
± sonolucent rim	Post-contrast images	± foci of high signal intensity11
CEUS	Nodules do not enhance9	± hyper-/hypointense rim
Arterial and portal venous enhancement similar to the surrounding liver parenchyma	Diffuse or peripheral rim-like enhancement10	Fat suppressed images decreased signal intensity12
		T2-weighted images
		Iso-/hypointense
		± hyperintense rim
		Enhancement pattern
		Similar to normal liver parenchyma13
Hepatic adenoma
2D	Pre-contrast examination	T1- and T2-weighted images
Heterogeneous	Hypoattenuating, sharply delineated spherical mass ± pseudocapsule	Heterogeneous, predominantly hyperintense20
Hyperechoic14/hypoechoic15/cyst-like16	Heterogeneous content17	In-phase and out-of-phase T1 sequence
Doppler US	Arterial phase	Signal loss (fatty components)
Central vessels with a triphasic pattern/continuous venous waveform	Homogeneous18/heterogeneous enhancement19	Enhancement pattern
CEUS	Portal venous and delayed phases	Early arterial enhancement
Only arterial enhancement as the distinctive feature to FNH	Isoattenuating/rapid “wash-out”	Isointense during portal and venous phases21
		Hepatocyte-specific contrast agents
		Hypointense on hepatocyte phase imaging

¹Hommogeneous/inhomogeneous (inhomogeneity is most frequently encountered in larger lesions, possibly be due to calcifications, hemorrhage, necrosis, thrombosis, and/or fibrosis);

²Hemorrhage;

³Small lesions;

⁴Larger lesions;

⁵Solid component may be hyper-/isoechoic as reported to the surrounding liver parenchyma;

⁶According to the type of the lesion (cystic/mixed/solid form);

⁷Calcifications, necrosis, bleeding, and internal debris are rare features. When present, the imaging aspect of the lesion is inhomogeneous;

⁸Often not visible due to small size and isoechogenicity. In these cases, a diffusely heterogeneous echotexture associated with distortion of hepatic architecture can be the only sonographic feature. Also, in rare cases, nodules can be hyperechoic ± hypoechoic centers (hemorrhage);

⁹Usually;

¹⁰Occasionally;

¹¹Hemorrhage;

¹²Intracellular fat;

¹³Preferentially in the portal venous phase;

¹⁴High lipidic content/recent hemorrhage;

¹⁵In glycogen storage diseases due to diffuse fatty infiltration of the liver;

¹⁶Mimicking a cyst, in cases of old blood content;

¹⁷Due to fat, calcifications, necrosis, or recent hemorrhage (hyperattenuating);

¹⁸Small lesions;

¹⁹Larger lesions due to areas of fat, hemorrhage, necrosis, or calcifications;

²⁰May also be due to hemorrhage;

²¹May present with late wash-out and a pseudocapsule may be visible on delayed acquisition. US: Ultrasound; CEUS: Contrast-enhanced ultrasound.