Cross-Sectional Anatomy LIVER Part 2 HHHoldorf

Segmental Liver Anatomy Traditionally, the liver has been described as having four lobes, namely, right, left, caudate, and quadrate. With the advent of surgical resection of focal hepatic lesions, the gross lobar anatomy has been modified to reflect the surgical approach which is based on segmental divisions.

Couinaud Segment 1 Caudate lobe 2 Left lobe, lateral segment 3 Left lobe, lateral segment 4 Left lobe, medial segment 5 Right lobe, anterior segment 6 Right lobe, anterior segment 7 Right lobe, posterior segment 8 Right lobe, posterior segment

Couinaud classification

The Couinaud classification of liver anatomy divides the liver into eight functionally independent segments. Each segment has its own vascular inflow, outflow and biliary drainage. In the centre of each segment there is a branch of the portal vein, hepatic artery and bile duct. In the periphery of each segment there is vascular outflow through the hepatic veins.

Right hepatic vein divides the right lobe into anterior and posterior segments. Middle hepatic vein divides the liver into right and left lobes (or right and left hemi liver). This plane runs from the inferior vena cava to the gallbladder fossa. Left hepatic vein divides the left lobe into a medial and lateral part. Portal vein divides the liver into upper and lower segments. The left and right portal veins branch superiorly and inferiorly to project into the center of each segment.

Because of this division into self-contained units, each segment can be resected without damaging those remaining. For the liver to remain viable, resections must proceed along the vessels that define the peripheries of these segments. This means, that resection- lines parallel the hepatic veins, The centrally located portal veins, bile ducts, and hepatic arteries are preserved.

Segmental liver anatomy is based on fissures which contain the major hepatic veins and or ligaments which are easily identified with ultrasound and CT imaging. The hepatic veins course between the hepatic lobes and segments, whereas the portal vessels are essentially within the liver lobes and segments. With segmental liver anatomy, here are three lobes and four segments to consider…

The MAIN LOBAR FISSURE divides the right and left lobes The MAIN LOBAR FISSURE divides the right and left lobes. This fissure is identified by the middle hepatic vein superiorly, and by an echogenic line between the right portal vein and the gallbladder inferiorly. The echogenic line represents fibro-fatty tissue in the main lobar fissure. It may be a useful landmark in identifying a contracted or stone-filled gallbladder (or a porcelain gallbladder).

The right inter-segmental fissure divides the right lobe into anterior and posterior segments. The only landmark which identifies this fissure on ultrasound is the right hepatic vein.

The left inter-segmental fissure divides the left lobe into medial and lateral segments (part of the medial segment is the quadrate lobe). This fissure may be identified by three landmarks on ultrasound: left hepatic vein (superior portion) anterior turn of the left portal vein (middle portion) Falciform ligament and Ligamentum teres (inferior portion)

The left portal vein has a characteristic “hook” configuration on Sagittal scans. The Ligamentum teres or round ligament of the liver is the obliterated umbilical vein from embryological development. It courses along the undersurface of the Falciform ligament between the umbilicus and the inferior portion of the left intersegmental fissure. The Ligamentum teres separates from the Falciform ligament and extends to the left portal vein (with which it communicated in fetal life). On Sagittal section, it appears as a linear echo dense structure. ON transverse section, the Ligamentum teres is seen as a circular structure. Strong attenuation by the Ligamentum teres may cause acoustic shadowing and it may be mistaken for a calcified lesion

The CAUDATE lobe has four distinct sonographic landmarks: IVC posterior Proximal portion of the left portal vein- antero-inferior fissure of the Ligamentum venosum-left anteriolateral margin main portal vein-inferior The caudate lobe is supplied by branches of the left and right portal venous and hepatic arterial systems, and is drained by small caudate veins which enter directly into the IVC. The caudate vessels are infrequently seen in normal patients.

Caudate lobe

Caudate Lobe. The caudate lobe (c) is between the inferior vena cava (I) and the fissure of the ligamentum venosum (long arrow). The inferior vena terminates in the right atrium (A). The curved arrow indicates the right hepatic vein. Also seen are the portal vein (p) and the hepatic artery (short arrow).

The caudate lobe is situated upon the postero-superior surface of the liver on the right lobe of the liver, opposite the tenth and eleventh thoracic vertebrae. It is bounded on the left side by the ligamentum venosum. It is bounded, below, by the portal vein; on the right, by the fossa for the inferior vena cava, and on the left by the fossa for the ductus venosus.

Location: Right inter-segmental fissure Anatomic structures useful for dividing and identifying the hepatic segments Structure: RHV Location: Right inter-segmental fissure Usefulness: Divides cephalic aspect of anterior and posterior segments of right lobe. Structure: MHV Location: Main Lobar Fissure Usefulness: Separates right and left lobes

Structure: LHV Location: Left inter-segmental fissure Usefulness: Divides cephalic aspects of medial and lateral segments of left lobe Structure: RPV (anterior branch) Location: Intra-segmental in anterior segment of right lobe Usefulness: Courses centrally in anterior segment of right lobe.

Structure: RPV (posterior branch) Location: Intra-segmental in posterior segment of right lobe Usefulness: Courses centrally in posterior segment of right lobe. Structure: LPV (horizontal segment) Location: Anterior to caudate lobe Usefulness: Separates caudate lobe Posteriorly from medical segment of left lobe anteriorly.

Structure: LPV (ascending segment) Location: Left inter-segmental fissure Usefulness: Divides medal and lateral segments of left lobe Structure: GB fossa Location: Main Lobar fissure Usefulness: Separates right and left lobes Structure: Fissure for the Ligamentum teres Usefulness: Divides caudal aspect of left lobe into medial and lateral segments. Structure: Fissure for the Ligamentum venosum Location: left anterior margin of caudate lobe Usefulness: Separates caudate lobe Posteriorly from left lobe anteriorly.

Ligamentum teres: Ligamentum Venosum: Round appearance on transverse view. Represents the remnant of fetal umbilical vein. Ligamentum Venosum: Remnant of the ductus venosus of the fetal circulation.

HOMEWORK Create a storyboard explaining the segmental anatomy of the liver. Utilize diagrams, ultrasounds, and CT scans Include in your story board the following: Left portal vein-the bifurcation of the left portal vein into medial and lateral branches demonstrated on a transverse scan.

The hepatic veins (transverse sub costal scan of the liver – showing the three main hepatic veins. showing the following Right lobe left lobe anterior segment posterior segment lateral segment medial segment right hepatic vein middle hepatic vein left hepatic vein inferior vena cava

Normal liver segmental anatomy showing the right portal vein- transverse sub costal scan of the liver showing the right portal vein dividing to anterior and posterior branches. The echo texture of the normal liver Main lobar fissure left, right, caudate lobe Fissure of the Ligamentum teres Fissure of the Ligamentum venosum GB fossa