Imaging features and management of focal liver lesions

Table 1 Technical considerations for computed tomography and magnetic resonance imaging

	CT	MRI
Recommended equipment	Multidetector CT with minimum of 8 detector rows	1.5 Tesla or 3 Tesla
	≤ 5 mm axial reconstructed slice thickness	Phased array multichannel torso coil
	Dual-chamber injector with a saline flush	Current-generation high-speed gradients
		Dual-chamber power injector
Contrast injection rate	≥ 3 mL/s of contrast, ≥ 300 mg iodine/mL	2-3 mL/s of gadolinium chelate
	1.5 mL/kg of body weight
Required images	Arterial phase (late arterial phase strongly preferred over early arterial phase)	Unenhanced T1-weighted in phase and opposed phase imaging
	Portal venous phase	T2-weighted imaging (fat suppression optional)
	Delayed phase	All contrast agents: Multiphase T1-weighted imaging, preferably using a three dimensional sequence with ≤ 5 mm slice thickness
		Pre-contrast imaging
		Arterial phase (late arterial phase strongly preferred over early arterial phase)
		Portal venous phase
		MRI with extracellular contrast agents or gadobenate dimeglumine
		Delayed phase (2 to 5 minutes after injection)
		MRI with gadoxetate disodium
		Transitional phase (2 to 5 minutes after injection)
		Hepatobiliary phase (about 20 minutes after injection)
Suggested images	Pre-contrast, for initial diagnosis and patients treated with local-regional therapy	Multi-planar acquisition
	Multi-planar reformations	Subtraction imaging
	Thinner slices with section thickness ≤ 3 mm	Diffusion-weighted imaging
		1-3 hours hepatobiliary phase with gadobenate dimeglumine
Dynamic phases	Bolus tracking or fixed timed delay is suggested	Bolus tracking or fixed timed delay is suggested

Technical considerations for computed tomography and magnetic resonance imaging[4,6,10]. CT: Computed tomography; LI-RADS: Liver imaging reporting and data system; MRI: Magnetic resonance imaging.

Table 2 Variants of incidental liver lesions and recommended appropriate imaging recommended by American College of Radiology

Variants	Initial imaging	Size	Extrahepatic malignancy	Underlying chronic liver disease	Appropriate imaging
Variant 1	US	> 1 cm	No	No	US abdomen with IV contrast
					MRI abdomen without and with IV contrast
					CT abdomen with IV contrast multiphase
Variant 2	CT (non-contrast or single-phase)	> 1 cm	No	No	MRI abdomen without and with IV contrast
	MRI (non-contrast)				CT abdomen with IV contrast multiphase
Variant 3	US	> 1 cm	Yes	No	MRI abdomen without and with IV contrast
					CT abdomen with IV contrast multiphase
Variant 4	CT (non-contrast or single-phase)	> 1 cm	Yes	No	MRI abdomen without and with IV contrast
	MRI (non-contrast)				CT abdomen with IV contrast multiphase
					FDG-PET/CT skull base to mid-thigh
Variant 5	US	> 1 cm	No	Yes	US abdomen with IV contrast
	CT (non-contrast or single-phase)				MRI abdomen without and with IV contrast
	MRI (non-contrast)				CT abdomen with IV contrast multiphase
Variant 6	US	< 1 cm	Yes	No	MRI abdomen without and with IV contrast
Variant 7	CT (non-contrast or single-phase)	< 1 cm	Yes	No	MRI abdomen without and with IV contrast
	MRI (non-contrast)				CT abdomen with IV contrast multiphase
Variant 8	US	< 1 cm	No	Yes	MRI abdomen without and with IV contrast
	CT (non-contrast or single-phase)				CT abdomen with IV contrast multiphase
	MRI (non-contrast)

Variants of incidental liver lesions and recommended appropriate imaging recommended by American College of Radiology[9]. ACR: The American College of Radiology; CT: Computed tomography; IV: Intravenous; MRI: Magnetic resonance imaging; US: Ultrasound; FDG-PET: Fluorodeoxyglucose positron emission tomography.

Table 3 Imaging features of common liver lesions

	US	CT (non-contrast)	MRI	Enhancement pattern (CT and MRI)
Hepatic hemangioma	Hyperechoic	Hypodense well-defined homogeneous lesion	T1: Hypointense	Arterial phase: Discontinuous, peripheral, nodular
	Well-defined homogeneous		T2: Markedly hyperintense	Enhancement
	lesions with acoustic enhancement			Portal venous and delayed phases: Progressive
	Rarely hypoechoic due to hepatic steatosis			Centripetal filling
				Hepatobiliary phase: Pseudo washout
Focal nodular hyperplasia	Difficult to detect (stealth lesion)	Difficult to detect (stealth lesion)	T1: Homogeneous isointense to slightly hypointense with hypointense stellate central scar	Arterial phase: Intense, homogenous enhancement
				Portal venous and delayed phases: Isointense or slightly hyperintense to the liver parenchyma
	Variable echogenicity	Hypodense or isodense well-defined lesions
			T2: Isointense to slightly hyperintense
			± Hyperintense central scar
				Hepatobiliary phase: Isointense or slightly hyperintense to the liver parenchyma
				± Central scar: Enhanced with extracellular gadolinium contrast agents, but not enhanced with HSCA
Hepatocellular adenoma	Heterogenous, well-defined lesions	Well-defined heterogenous lesion	T1: Variable signal intensity loss of signal	Arterial phase: Intense enhancement
	Highly variable echogenicity	± Hyperdense if hemorrhagic
		± Hypodense if fatty	On opposed-phase if fatty
		± Calcification in areas of old hemorrhage	T2: Hyperintense
Hepatic cyst	Anechoic, well-defined, homogenous lesion	Well-defined homogenous, hypodense lesion	T1: Hypointense	No enhancement with contrast agents
			T2: Hyperintense
			Well-defined, homogenous lesion
Polycystic liver disease	Multiple cysts with features, resembling hepatic cysts US findings	Multiple cysts with features, resembling hepatic cysts CT findings	Multiple cysts with features, resembling hepatic cysts MRI findings	No enhancement with contrast agents
Mucinous cystic neoplasm of liver	Solitary, well-defined, multiloculated anechoic lesion with septations	Well defined heterogenous lesion	T1: Variable signal intensity	± Enhancement of wall/septations
		± Calcification	T2: Hyperintense
	± Septal/mural nodules
	± Calcification
Cholangiocarcinoma	Heterogenous	Heterogenous hypodense lesion with capsular retraction and parenchymal atrophy	T1: Heterogeneous hypointense	Arterial phase: Peripheral, enhancement (targetoid appearance)
	Variable echogenicity
	± Hypoechoic rim		T2: Peripherally hyperintense and centrally hypointensite	Portal venous and delayed phases: Progressive, persistent heterogeneous enhancement
	± Dilated intrahepatic bile ducts	± Dilated intrahepatic bile ducts
	± Satellite lesions	± Satellite lesions
		± Vascular encasement
Hepatocellular carcinoma	Variable echogenicity	Early HCC, isodense, ± hypodense if fatty	T1: Variable signal intensity, ± loss of signal	Arterial enhancement
				Portal venous, delayed and hepatobiliary phases: Washout
		Progressed HCC, isodense or hypodense, occasionally hyperdense	On opposed-phase if fatty
			T2: Variable signal intensity, typically moderately hyperintense

CT: Computed tomography; MRI: Magnetic resonance imaging; US: Ultrasound; HSCA: Hepatobiliary-specific contrast agents.

Table 4 Classification of hydatid cyst and imaging features

Gharbi	WHO-IWGE	US findings	CT findings	MRI findings
Type 1	CE1	Unilocular cyst with wall	Well-defined hypoattenuating cyst	T1 hypointense
		Hydatid sand	Perceptible wall with mild delayed enhancement	Very T2 hyperintense
		Snowstorm sign	No internal enhancement	Perceptible wall with mild delayed enhancement
		No internal vascularity		No internal enhancement
Type 3	CE2	Multilocular, multiseptated cyst	Multivesicular multiseptated cyst	Multivesicular multiseptated
		Honeycomb sign	Hypoattenuating daughter cysts	T2 hyperintense daughter cysts
		Daughter cysts	No septal enhancement	No septal enhancement
Type 2	CE3	Cyst with detached membrane, water-lily sign (CE3a)	Heterogeneous	Heterogeneous
		Cyst with daughter vesicles in a solid matrix (CE3b)	High-attenuating internal content	T2 hypointense detached membranes
			Detached membranes	No internal enhancement
			No internal enhancement
Type 4	CE4	Cyst with heterogenous content	Solid appearance	T2 iso- to hypointense
		No daughter cysts	No daughter cysts	No daughter cysts
		Ball of wool sign	Avascular	Avascular
Type 5	CE5	Thick calcified wall	Capsular and/or central calcifications	Very hypointense wall and intermediate to low internal signal intensity on T2-weighted images
			Complete calcification	No internal enhancement
			No internal enhancement

Classification of hydatid cyst and imaging features[119,121]. CT: Computed tomography; MRI: Magnetic resonance imaging; US: Ultrasound; WHO-IWGE: World Health Organization Informal Working Group on Echinococcosis.

Table 5 Stage-specific treatments of hepatic hydatid cysts recommended by World Health Organization Informal Working Group on Echinococcosis

WHO-IWGE classification	Surgery	Percutaneous treatment	Drug therapy	Suggested optimal treatment
CE1		Yes	Yes	< 5 cm
				Albendazole
				> 5 cm
				PAIR + Albendazole
CE2	Yes	Yes	Yes	Non-PAIR percutaneous treatment + Albendazole
CE3a		Yes	Yes	< 5 cm
				Albendazole
				> 5 cm
				PAIR + Albendazole
CE3b	Yes	Yes	Yes	Non-PAIR percutaneous treatment + Albendazole
CE4				Watch and wait
CE5				Watch and wait

Stage-specific treatments of hepatic hydatid cysts recommended by World Health Organization Informal Working Group on Echinococcosis[114]. PAIR: Puncture, aspiration, injection, and re-aspiration; WHO-IWGE: World Health Organization Informal Working Group on Echinococcosis.