DOI: 10.1148/radiol.2481051024
(Radiology 2008;248:317-318.)
© RSNA, 2008
The Right Posterior Hepatic Notch Sign1
Kok Chye Tan, MBBS, FRCR
1 From the Department of Oncologic Imaging, National Cancer Centre, 11 Hospital Dr, Singapore 169610, Republic of Singapore. Received June 18, 2005; revision requested August 18; revision received November 13; final version accepted March 13, 2006.
Address correspondence to the author (e-mail: tankokchye{at}yahoo.com).
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APPEARANCE
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The posterior hepatic notch sign is seen on axial computed tomography (CT) and magnetic resonance (MR) images as a sharp indentation on the posteroinferior liver surface between the caudate and right lobes (Figure).
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EXPLANATION
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On CT and MR images, the posteroinferior surface of the right hepatic lobe at the level of the right kidney is normally concave owing to the renal impression. In patients with cirrhosis, a sharp indentation different from the renal impression often develops between the caudate and right lobes of the liver (1). Although the exact mechanism is unclear, it is believed that the right posterior hepatic notch sign may be caused by enlargement of the caudate lobe and atrophy of the right lobe in patients with liver cirrhosis (1).
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DISCUSSION
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Enlargement of the caudate lobe and atrophy of the right lobe are well-known morphologic changes in cirrhotic livers (2,3). As cirrhosis progresses, common findings include atrophy of the right lobe, particularly posterior segments VI and VII, as well as enlargement of the caudate lobe (segment I) and lateral segments II and III of the left lobe (4).
The causes of caudate lobe enlargement and right lobe atrophy are unclear but are thought to be linked to alterations in portal blood flow; blood in the main portal vein does not mix well, and "streaming" occurs (5). One theory is that the right lobe receives most of its blood from the superior mesenteric vein and, hence, is more exposed to toxins (eg, alcohol, which is absorbed from the small intestines). The left hepatic lobe, however, receives most of its blood from the splenic vein and is more exposed to pancreatic hormones (eg, insulin) that promote hypertrophy (6,7). This theory is not accepted by all (8). The caudate lobe is predominantly supplied by the left branches of the portal vein or by branches from the bifurcation of the portal vein. The intrahepatic branches to the caudate lobe are shorter than the right lobe of the liver (9). One may postulate that the caudate lobe hypertrophies because it is predominantly supplied by the splenic vein with all its trophic pancreatic hormones and because the flow to it is also increased by the short branches of the supplying portal veins (10). Although these theories may explain the findings, further proof is required to validate them.
Several investigators have used various ratios based on the above findings of enlargement of the left and caudate lobes with atrophy of the right lobe for the diagnosis of cirrhosis. Giorgio et al (11) and Hess et al (2) have described a number of indexes as quantitative markers to evaluate cirrhosis, including the ratio of transverse caudate lobe width to right lobe width, multidimensional caudate lobe indexes that can be obtained by using ultrasonography (US) or CT, and volume analysis of each liver segment on the basis of cross-sectional area measured on CT or MR images. Harbin et al (12) chose the bifurcation of the main portal vein, a reproducible landmark, to divide the caudate lobe from the right lobe. A ratio of 0.65 was considered sensitive and specific for liver cirrhosis in their series.
Awaya et al (10) postulated that the right portal venous bifurcation more accurately divides the hypertrophied caudate from the atrophied right lobe. They showed that a modified caudate lobe–right lobe ratio, with the right border of the caudate lobe more laterally defined at the right portal vein bifurcation, could be used to more accurately diagnose cirrhosis. This more lateral landmark is coincident with the position of the posterior hepatic notch (1).
The sensitivity, specificity, accuracy, and positive predictive value of the right posterior hepatic notch sign for diagnosis of cirrhosis at MR imaging are 72%, 98%, 82%, and 99%, respectively (1). Coexistence of the expanded gallbladder fossa sign improved the sensitivity and accuracy to 86% and 89%, respectively (13). The expanded gallbladder fossa sign is considered to be present if there is enlargement of the pericholecystic space bounded laterally by the edge of the right hepatic lobe, medially by the lateral segment of the left hepatic lobe, and occasionally posteriorly by the anterior edge of the caudate lobe. It should be noted that the right posterior hepatic notch sign is seen in the normal liver in approximately 2% of the general population (1).
The right posterior hepatic notch sign provides a qualitative clinical alternative to the quantitative methods described above. The sign, however, does not relate to the clinical or pathologic severity of cirrhosis (1), which may alter the sensitivity and the accuracy of detection.
Okazaki et al (14) reported that enlargement of the caudate lobe and presence of the right posterior hepatic notch on MR images are more frequent findings in alcoholic cirrhosis than in virus-induced cirrhosis. The caudate lobe of patients with alcoholic cirrhosis tended to be larger than that of patients with viral infection because fibrosis is seen more frequently in alcoholic cirrhosis than in viral cirrhosis. Thus, the right posterior hepatic notch was more frequently visualized in alcoholic cirrhosis than in viral cirrhosis.
In conclusion, the right posterior hepatic notch represents the functional boundary between the enlarged caudate lobe and the atrophied right lobe and can be used as a highly indicative sign of cirrhosis.
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ACKNOWLEDGMENTS
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The author acknowledges Wilfred C. G. Peh, MBBS, FRCP, FRCR, for his help in the review of this manuscript.
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FOOTNOTES
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Author stated no financial relationship to disclose.
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References
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