• • CIRRHOSIS

Liver cirrhosis represents the terminal stage of various chronic diffuse liver diseases, having characteristic morphologic changes:

• • • • • Caudate lobe hypertrophy
        • Left lateral segment hypertrophy
        • Atrophy of the medial segment
        • Right lobe atrophy
        • Right posterior hepatic notch [6]

Caudate lobe hypertrophy is one of the main findings of cirrhosis and one of the first imaging biomarkers described for cirrhosis evaluation was the caudate/right lobe (C/RL) ratio; later it was further adjusted and presented as the modified C/RL ratio which has a greater specificity for cirrhosis. [3,7]

Fig 2: Caudate-right lobe ratio - abnormal value. While line - drawn to the lateral wall of the main portal vein bifurcation. Yellow line - drawn through the most medial margin of the caudate lobe. Axial CECT - venous phase. Image source: Radiology Department, Regional Institute of Gastroenterology - Cluj-Napoca/Romania 2018.

Fig 3: Modified caudate - right lobe ratio - abnormal value. White line - drawn to the right lateral wall of the right portal vein bifurcation. Yellow line - drawn through the most medial margin of the caudate lobe. Axial T2W image. Image source: Radiology Department, Regional Institute of Gastroenterology - Cluj-Napoca/Romania 2023.

Caudate lobe hypertrophy is also accountable for the right posterior hepatic notch, an indentation on the posterior liver surface between the right and caudate lobe.[8]

Fig 4: Alcoholic cirrhosis - caudate lobe hypertrophy (white arrows) in serial images. Posterior hepatic notch (orange arrow). Axial T2W sequence. Image source: Radiology Department, Regional Institute of Gastroenterology - Cluj-Napoca/Romania 2023.

The pathogenetic mechanism of caudate lobe hypertrophy in cirrhosis is probably multifactorial. One component is that the caudate vessels may be less compressed by hepatic fibrosis due to their short intraparenchymal course. Thus the caudate lobe receives a relatively greater blood supply through both the arterial and portal venous system resulting in caudate lobe hypertrophy. Another contributing factor is the particular venous outflow, which protects the caudate lobe from the increased portal hypertension.[3] 

Taking it a step further, caudate lobe hypertrophy may be one of the clues in differentiating various etiologies of cirrhosis. It has been observed that in early stages (Child-Pugh A), caudate lobe hypertrophy is more prominent in alcoholic and NASH etiologies and less obvious in viral-induced cirrhosis. Nevertheless, with disease progression, these characteristic features fade away. [6]  The differential portal blood supply may be responsible for this pattern of atrophy-hypertrophy complex: the right portal vein is hemodynamically supplied by the superior mesenteric vein, which drains the upper GI tract and contains higher concentration of alcohol and toxins thus the right lobe is more affected and becomes atrophic, while the caudate lobe is less affected and it goes compensatory hypertrophy. [9]

Fig 5: Hepatitis C cirrhosis. Morphologic changes: caudate lobe enlarged (white arrow); left lateral segment hypertrophy (orange arrow); left medial segment atrophy (blue arrow). Axial CECT - arterial phase. Image source: Radiology Department, Regional Institute of Gastroenterology - Cluj-Napoca/Romania 2023.

• • CAVERNOUS TRANSFORMATION OF THE PORTAL VEIN

Chronic portal vein thrombosis with cavernous transformation is oftentimes associated with liver disease, but it may also appear in the context of different systemic pathologies.  

Even when there is no liver pathology associated initially, the chronic nature of the disease induces secondary morphologic changes in the liver, with a recognizable pattern of atrophy-hypertrophy complex.

Morphologic changes:

• • • • • Caudate lobe hypertrophy
        • Left medial segment hypertrophy
        • Atrophy of the left lateral segment 
        • Right lobe atrophy

Fig 6: Portal cavernoma. Morphologic changes: caudate lobe hypertrophy; left medial segment hypertrophy; right lobe and left lateral segment atrophy. Axial CECT. Image source: Vilgrain V, Condat B, Bureau C, et al. Atrophy-hypertrophy complex in patients with cavernous transformation of the portal vein: CT evaluation. Radiology. 2006;241(1):149-155.

The proposed pathogenetic mechanism for these morphologic changes is that the caudate lobe and segment IV becomes hypertrophic due to their proximity to cavernous transformation, which results in maintained portal inflow while the right liver and left lateral segments have compromised portal flow. [10]

Fig 7: Portal cavernoma in a cirrhotic patient. Caudate lobe hypertrophy presenting a slightly different density than adjacent liver (“pseudotumor” appearance) - arrow in picture C. Axial CECT - portal-venous phase. Image source: Radiology Department, Regional Institute of Gastroenterology - Cluj-Napoca/Romania 2019.

• • IDIOPATHIC PORTAL HYPERTENSION

Idiopathic portal hypertension is a disease which affects small intrahepatic portal veins with consecutive development of presinusoidal PHT in the absence of liver cirrhosis. 

Morphologic changes:

• Caudate lobe hypertrophy 
• Left medial segment hypertrophy - occasionally
• Right lobe atrophy

Diagnostic imaging is particularly difficult as oftentimes it perfectly mimics cirrhosis. One of the most common findings regarding liver morphology was caudate lobe hypertrophy. Although sporadic, if associated with segment IV hypertrophy, this can be one of the diagnostic clues in differentiating idiopathic portal hypertension from cirrhosis. [11,12]

Fig 8: Idiopathic portal hypertension. Caudate lobe hypertrophy (arrows). Slightly enlarged left medial segment (dashed circle). Enlarged spleen (*). Axial CECT - portal-venous phase. Image source: Radiology Department, Regional Institute of Gastroenterology - Cluj-Napoca/Romania 2018.

• • CONGENITAL HEPATIC FIBROSIS

Congenital hepatic fibrosis is a rare genetic disorder usually affecting both the hepatic and renal system and sometimes associating other biliary duct anomalies.

Morphologic changes:

• Caudate lobe hypertrophy
• Left medial segment - normal or hypertrophic 
• Left lateral segment hypertrophy
• Right lobe atrophy [ 11]

Fig 9: Congenital hepatic fibrosis. Caudate lobe hypertrophy ( arrows) and enlarged left medial segment (dashed circle) - associating a different signal intensity than adjacent liver . Incidental splenic cystic lesion (*). Axial T2W sequence. Image source: Ramanathan S, Raghu V, Virmani V, Sheikh A, Al Heidous M, Tirumani S. Unveiling the unreal: Comprehensive imaging review of hepatic pseudolesions. Clin Imaging. 2021;80:439-453.

• • BUDD-CHIARI SYNDROME

Budd-Chiari syndrome is a disease characterised by hepatic venous outflow obstruction, most common secondary to hepatic veins thrombosis. 

Morphologic changes:

• Hypertrophy of the caudate lobe - may be the most remarkable feature
• Left lateral segment hypertrophy - occasionally

One of the main findings in chronic Budd-Chiari syndrome is the important hypertrophy of the caudate lobe. The pathogenetic mechanism is bound to the particular venous outflow directly into the inferior vena cava, sparing the caudate from the increased venous pressure - consequently the caudate lobe becomes enlarged.

While the mosaic enhancement pattern ( "nutmeg" liver) is commonly associated with Budd-Chiari syndrome, a relatively normal sized caudate lobe should suggest veno-occlusive disease or passive hepatic congestion instead, thus making caudate lobe hypertrophy an essential diagnostic finding. [13, 14]

Fig 10: Budd Chiari syndrome. Important hypertrophy of the caudate lobe (white arrows). Mosaic pattern of enhancement and regenerative nodules (yellow arrows). Axial CECT - arterial phase. Image source: Radiology Department, Regional Institute of Gastroenterology - Cluj-Napoca/Romania 2023.

• PRIMARY SCLEROSING CHOLANGITIS

Primary sclerosing cholangitis is a cholestatic disease characterised by progressive inflammation and fibrosis with multiple strictures of the intra and extrahepatic bile ducts. [15]

Morphologic changes:

• Caudate lobe hypertrophy
• Right lobe atrophy 
• Left lateral segment atrophy 
• Characteristic spherical shape - due to peripheral atrophy and prominent central hypertrophy
• Grossly lobulated contour - also due to the particular AHC complex

Fig 11: Primary sclerosing cholangitis. Spherical shape of the liver (dashed circle) with central hypertrophy and peripheral atrophy - caudate lobe hypertrophy (white arrows); left lateral segment atrophy (yellow arrows). Axial T2W sequence. Image source: Radiology Department, Regional Institute of Gastroenterology - Cluj-Napoca/Romania 2021.

The  pathogenetic mechanism through which the caudate lobe is apparently spared, undergoing compensatory hypertrophy in this disease, is unclear. One suggestion is that the most affected segments of the biliary tree are the main right and left bile ducts; as the caudate lobe bile ducts drain into the main left or right duct just before the confluence or directly into the common hepatic duct, often times the biliary flux of the caudate lobe is preserved, in an otherwise severely affected liver. [16] 

Another suggestion is that the compensatory hypertrophy of the central liver is due to alteration of intrahepatic hemodynamics. It has been observed that in PSC there is peripheral increased arterial enhancement with relative reduction of portal flow and, contrarily, portal flow is preserved in the central liver. As liver volume is dependent on portal blood, the central liver, including caudate lobe, undergoes compensatory hypertrophy. [15]

Primary biliary cirrhosis (PBC) is another cholestatic disease, with rather nonspecific imagistic findings, often overlapping those of cirrhosis of other etiologies. Although not so notorious, sometimes it can also present with prominent caudate lobe enlargement, thus PBC must be in the differential diagnosis in such cases. [17]

• • WILSON DISEASE

Wilson disease is a genetic disorder of copper metabolism which progressively affects liver function, in advanced disease featuring typical morphologic findings of cirrhosis, except caudate lobe enlargement.

In this case, the absence of caudate lobe hypertrophy  and a normal C/RL ratio even in advanced stages is an important imagistic feature and one must suggest this as the leading diagnosis in a young cirrhotic patient. [18]

Fig 12: Wilson disease - cirrhotic liver. Normal size of caudate lobe. Axial NECT. Image source: Akhan O, Akpinar E, Karcaaltincaba M, et al. Imaging findings of liver involvement of Wilson's disease. Eur J Radiol. 2009;69(1):147-155.

• • PITFALL - PROMINENT PAPILLARY PROCESS OF CAUDATE LOBE

At the inferior border, the caudate lobe is divided into a lateral caudate process and a papillary process, situated medially. A prominent papillary process represents an anatomical variant and is usually an incidental finding, but it may mimic an enlarged lymph node or a pancreatic mass on cross-sectional imaging.

It might also be misinterpreted as a pathologically enlarged caudate lobe but the lack of any additional findings of liver disease should promptly indicate the right diagnosis. [19]

Fig 13: Prominent papillary process. No liver pathology associated. Axial NECT. Case courtesy: Dr Diana Raluca Petea-Balea - Cluj-Napoca/Romania 2022.