Liver involvement in patients with COVID-19 infection: A comprehensive overview of diagnostic imaging features

Table 1 Summary of the most common findings in liver involvement due to coronavirus disease 2019 infection

Liver involvement	Ultrasound	Computed tomography	Magnetic resonance
Hepatomegaly	Qualitative criteria: The right lobe extends inferiorly over the lower pole of the right kidney; Rounding of the hepatic inferior border
	Quantitative criterion: Length of the right liver lobe > 16.5 cm
Steatosis	Hyperechoic liver in comparison to the spleen or neighboring kidney; Absence of the normal echogenic walls of the portal and hepatic veins; Poor visualization of deep portions of the liver	Unenhanced: Relative hypoattenuation: liver attenuation more than 10 HU less than that of spleen; Absolute low attenuation: liver attenuation lower than 40 HU; C+: Does not add information	IP/OOP imaging: Signal drop out on OOP; T2W: Isointense; T1: Isointense; T1 C+: Does not add significant information
Acute hepatitis	Hepatomegaly; Reduced echogenicity; Steatosis; Peri-portal edema; Reduced Doppler signal in the hepatic artery; Thickening of the gallbladder wall	Hepatomegaly; Homogeneous/heterogeneous hypoattenuation (steatosis); Peri-portal edema; Thickening of the gallbladder wall; Periportal/hepatoduodenal enlarged nodes	IP/OOP imaging: Steatosis can be present; T2W: Diffuse mild increase in signal; Increased signal around the portal system (periportal edema); T1 C+: Periportal enhancement; Thickening of the gallbladder wall; Hilar enlarged nodes
DILI	Nonspecific findings: Hepatomegaly, steatosis, and peri-portal edema can be present
Portal vein thrombosis	Absent or reduced flow in the portal vein on Color Doppler; Presence of heterogeneous material (focal or diffuse) in the portal vein lumen	Unenhanced: Higher attenuation into the portal vein lumen; Dilation of the portal trunk; C+: Hypoattenuating material into the lumen; Enhancement of vein walls	T2W: Iso- to hyperintense clot according to the phase (acute or subacute); T1: Hyperintense clot; T1 C+: Hypointense material into the lumen; Enhancement of vein walls
Biliary involvement	Focal or diffuse bile duct dilatation (with/without intrahepatic or extrahepatic stones)	Unenhanced: Does not add information; C+: Focal or diffuse bile duct dilatation (with/without intrahepatic or extrahepatic stones); Heterogeneous enhancement of parenchyma; Peri-portal edema	MRCP: Focal or diffuse bile duct dilatation with/without intrahepatic or extrahepatic stones; Stone(s) in the biliary lumen (hypointense); Multifocal biliary strictures alternated with dilated tracts (beaded appearance); T2W: Hypointense stone; Increased T2 signal around the portal system (periportal edema); T1: Hyperintense stone; T1 C+: Heterogeneous enhancement of peri-biliary parenchyma
Acute cholecystitis	Gallbladder wall thickening (> 3 mm); Pericholecystic fluid; Gallbladder distension; Possible sludge	Unenhanced: Gallbladder distension; Possible sludge (hyperattenuating); Pericholecystic fluid; C+: Gallbladder wall thickening (> 3 mm); Inhomogeneous gallbladder wall; Mural or mucosal hyperenhancement	MRCP: May show an impacted stone in the gallbladder neck or cystic duct; T2W: Gallbladder wall thickening (> 3 mm); Inhomogeneous gallbladder wall due to edema; T1: Sludge (hyperattenuating); T1 C+: Inhomogeneous gallbladder wall; Mural or mucosal hyperenhancement

HU: Hounsfield unit; IP: In-phase; OOP: Out-of-phase; C+: Contrast-enhanced; DILI: Drug-induced liver injury; MRCP: Magnetic resonance cholangiopancreatography.