The liver has eight segments, which are referred to by numbers or by names. The numbering of the segments is done in a counterclockwise manner with the liver being viewed from the inferior surface, starting from Segment I (the caudate lobe). Standard anatomical description of the liver segments is available by computed tomographic scan and ultrasonography. Endoscopic ultrasound (EUS) has been used for a detailed imaging of many intra-abdominal organs and for the assessment of intra-abdominal vasculature. A stepwise evaluation of the liver segments by EUS has not been described. In this article, we have described a stepwise evaluation of the liver segments by EUS. This information can be useful for planning successful radical surgeries, preparing for biopsy, portal vein embolization, transjugular intrahepatic portosystemic shunt, tumour resection or partial hepatectomy, and for planning EUS guided diagnostic and therapeutic procedures.

Endoscopic ultrasound (EUS) can demonstrate the detailed anatomy of the liver from the transgastric and transduodenal routes. Most of the liver segments can be imaged with EUS, except the right posterior segments. The intrahepatic vascular landmarks include the major hepatic veins, portal vein radicals, hepatic arterial branches, and the inferior vena cava, and the venosum and teres ligaments are other important intrahepatic landmarks. The liver hilum and gallbladder serve as useful surface landmarks. Deciphering liver segmentation and anatomy by EUS requires orienting the scan planes with these landmarkstructures, and is different from the static cross-sectional radiological images. Orientation during EUS requires appreciation of the numerous scan planes possible in real-time, and the direction of scanning from the stomach and duodenal bulb. We describe EUS imaging of the liver with a curved linear probe in a step-by-step approach, with the relevant anatomical details, potential applications, and pitfalls of this novel EUS application.

To study the visibility of the caudate vein and its diameter on MR imaging in healthy people and in patients with Budd-Chiari syndrome.

In this study there were 14 patients with Budd-Chiari syndrome and 54 healthy subjects without hepatic lesion or liver disease, all of whom had upper abdominal enhanced MRI. The visibility of the caudate vein and its diameter on MR images was compared between Budd-Chiari patients and healthy subjects, and among Budd-Chiari patients, the correlation between the visibility of caudate vein and extrahepatic collaterals were compared.

Caudate vein was noted in 64% of patients with Budd-Chiari syndrome and in 7% of healthy subjects (P=0.000). The diameter of the caudate vein visualized on MR imaging in Budd-Chiari syndrome was significantly larger than that in healthy group (7.3±3.9 mm vs 2.6±0.6 mm, P=0.037). Among Budd-Chiari patients, both caudate vein and extrahepatic collateral veins were noted in 9 patients, only extrahepatic collateral veins were noted in 4 patients and neither caudate vein nor extrahepatic collateral veins were noted in 1 patient. No correlation was found between the visibility of caudate vein and that of extrahepatic collateral vein in patients with Budd-Chiari (P=0.375).

Gadolinium enhanced dynamic MR imaging can visualize hepatic caudate vein frequently. The visibility and dilation of hepatic caudate veins on MR imaging in Budd-Chiari syndrome were more frequent than in control subjects. MR depiction of a caudate vein may help differentiate Budd-Chiari from cirrhosis.

The aim of this study was to evaluate the usefulness of sonography in measuring the caudate vein and lobe when diagnosing Budd-Chiari syndrome.

Our study included a group of 16 patients with Budd-Chiari syndrome. We compared this patient group with a control group of 40 patients with cirrhosis and 66 healthy subjects without liver disease. On sonography, we measured the diameter of the caudate lobe and the presence and diameter of the caudate vein. These measurements were then compared for both groups.

In half of the patients with Budd-Chiari syndrome, sonography showed a visible caudate vein (3-21 mm; mean, 7.3 mm; median, 4.6 mm). However, in the control group, spontaneous visualization was seen in only eight (7.5%) of 106 subjects, none of whom had cirrhosis. The caudate lobe was larger in patients with cirrhosis than in healthy subjects. Likewise, in patients with Budd-Chiari syndrome, the caudate lobe was larger than that in patients with cirrhosis.

When sonography reveals a caudate vein equal to or larger than 3 mm in diameter in the appropriate clinical setting, one should strongly suspect Budd-Chiari syndrome.

The segmental anatomy of the human liver has become a matter of increasing interest to the radiologist, especially in view of the need for an accurate preoperative localization of focal hepatic lesions. In this review article first an overview of the different classical concepts for delineating segmental and subsegmental anatomy on US, transaxial CT, and MR images is given. Essentially, these procedures are based on Couinaud's concept of three vertical planes that divide the liver into four segments and of a transverse scissura that further subdivides the segments into two subsegments each. In a second part, the limitations of these methods are delineated and discussed with the conclusion that if exact preoperative localization of hepatic lesions is needed, tumor must be located relative to the avascular planes between the different portal territories.

The papillary process of the caudate lobe can extend posteriorly to lie between the inferior vena cava (IVC) and aorta. Occasionally, the papillary process can wrap around the IVC such that its tip lies posterior to the inferior vena cava. These positions of the papillary process create the potential for its misdiagnosis as a lymph node or mass on coronal and sagittal MRI. To evaluate the frequency that this variant occurs, we retrospectively evaluated contrast axial CT scans in 113 adult patients. Ninety-seven percent had a portion of their papillary process extending posterior to the anterior margin of the IVC. In 66% of the patients, the papillary process overlapped more than 50% of the IVC. In these patients, the papillary process would likely appear as a separate soft tissue structure between the IVC and aorta on coronal MRI. In 12 patients, the papillary process not only extended posterior to lie between the IVC and aorta, but actually extended behind a portion of the inferior vena cava as well. This position of the papillary process could appear as a separate soft tissue structure between the IVC and the diaphragmatic crus on sagittal MRI. The posterior extent of the papillary process between the inferior vena cava and aorta, and occasionally, behind the inferior vena cava, are common anatomical variants, knowledge of which may prevent misdiagnosis on coronal and sagittal MRI.

Although there are many complementary and supplementary types of diagnostic imaging of the liver, a logical sequence for most liver pathology begins with high-quality ultrasound. It is noninvasive and inexpensive but very operator dependent. In other settings, CT may be the preferable screening modality, as it gives an excellent picture of the global anatomy and is easily reproducible. Frequently, the two modalities are complementary and indicated; on other occasions, one method will suffice. Radionuclide evaluation of the liver is usually reserved for hepatobiliary imaging for biliary obstruction or the question of acute cholecystitis and tagged-red cell scanning for hemangioma. It is also frequently used for gallium scanning in hepatoma, but lymphoma and inflammatory diseases are also gallium avid. The invasive imaging tests of the liver--angiography and transhepatic and endoscopic retrograde cholangiography--are performed when insufficient information is obtained by the other methods (as in diagnostic transhepatic cholangiography) or when the procedure offers therapy (as for biliary drainage, percutaneous transhepatic removal of common bile duct stones, percutaneous cholecystosis with gallstone dissolution and liver embolization, or the angiographic evaluation for portal shunting or liver resection). The impact of magnetic resonance imaging and fourth-generation raid angiotomography CT scanning has yet to be felt. The use of intraoperative ultrasound is to be encouraged prior to liver resection because it can demonstrate lesions as small as 3 mm in diameter.