US CT and MRI findings in cirrhosis
US: The hepatic parenchyma in cirrhosis is typically heterogeneous and hyperechoic with “coarsened” echoes and poorly defined intrahepatic vasculature. Unfortunately, these findings are nonspecific, with increased parenchymal echogenicity also present in fatty infiltration, and parenchymal heterogeneity also present in infiltrating neoplasms. Sonographic features with greater specificity for cirrhosis include nodularity of the liver surface and relative enlargement of the caudate lobe. A caudate-to-right lobe volume ratio of more than 0.65 is highly specific but not sensitive in diagnosing cirrhosis.
MDCT: In cirrhosis, the caudate lobe and left-lateral segment typically enlarge, and the right lobe and left-medial segment typically atrophy, resulting in an enlarged gallbladder fossa. Enlargement of the hilar periportal space, as a result of atrophy of the left lobe medial segment, is more than 90% sensitive and specific for early cirrhosis. In advanced cirrhosis, liver volume usually decreases and periportal fibrosis and regenerative nodules can compress the portal and hepatic venous structures, which may result in altered hepatic perfusion and portal hypertension. The presence of isodense regenerating nodules can often only be inferred from the nodular contour of the liver edge. Complications of portal hypertension, especially varices, are exquisitely demonstrated with MDCT; however, unlike sonography, CT cannot determine the direction of vascular flow. Increased attenuation of the mesenteric fat is also noted.
MRI: MRI findings in cirrhosis are similar to those on MDCT, with early changes manifesting as enlargement of the hilar periportal space as a result of atrophy of the left lobe medial segment and later findings presenting as a caudate/right hepatic lobe ratio of more than 0.65 and an expanded gallbladder fossa sign. Regenerative nodules are usually smaller than 1 cm in diameter, have variable T1-w signal, and usually iso to decreased T2-w and gradient-recalled echo (GRE) signal. Regenerative nodules are usually isointense to liver following contrast. Dysplastic nodules are considered premalignant and are usually larger than regenerative nodules. They often demonstrate increased T1-w and decreased T2-w signal; however, there is overlap with hepatocellular carcinoma (HCC). Imaging findings of portal hypertension are similar to those on MDCT and initially include dilation of the portal and splenic veins with later occlusion and cavernous transformation of the PV and development of portosystemic collaterals and ascites.