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The hepatic lobule is a building block of the liver tissue, consisting of portal triads, hepatocytes arranged in linear cords between a capillary network, and a central vein. Lobules are different from the lobes of liver : they are the smaller divisions of the lobes.
The right vertical limb of the "H" defines the left and right functional lobes, while the left vertical limb of the "H" defines the right and left anatomical lobes. The horizontal line between the vertical limbs of the "H" represents the porta hepatis. The quadrate and caudate lobe lie superior and inferior to this line respectively.
The quadrate lobe is an area of the liver situated on the undersurface of the medial segment left lobe (Couinaud segment IVb), bounded in front by the anterior margin of the liver, behind by the porta hepatis, on the right by the fossa for the gall-bladder, and on the left by the fossa for the umbilical vein.
A liver segment is one of eight segments of the liver as described in the widely used Couinaud classification (named after Claude Couinaud) in the anatomy of the liver.This system divides the lobes of the liver into eight segments based on a transverse plane through the bifurcation of the main portal vein, [1] arranged in a clockwise manner starting from the caudate lobe.
During the portal venous phase there is a specific "wash out" of ultrasound contrast agent (UCA) and the tumor appears hypoechoic during the late phase. Poorly differentiated tumors may have a stronger wash out leading to an isoechoic appearance to the liver parenchyma during portal venous phase. This appearance was found in approx. 30% of cases.
Selected images from a biphasic CT of Focal Nodular Hyperplasia in the left hepatic lobe (arrow). These masses have characteristic early arterial enhancement (6a) with contrast wash out on the portal venous phase images (6b) from the mass making these lesions difficult to identify on portal venous phase images alone. [citation needed]
The central vein joins to the hepatic vein to carry blood out from the liver. A distinctive component of a lobule is the portal triad, which can be found running along each of the lobule's corners. The portal triad consists of the hepatic artery, the portal vein, and the common bile duct. [25]
It is formed by the union of the right hepatic duct (which drains bile from the right functional lobe of the liver) and the left hepatic duct (which drains bile from the left functional lobe of the liver). [3] The duct is about 3 cm long. [4] The common hepatic duct is about 6 mm in diameter in adults, with some variation. [5]