Chapter 12: Liver

Location of Liver

Occupies the major portion of the right hypochondrium/hypochondriac region; extends inferiorly into the epigastrium and laterally into the left hypochondrium

Liver Anatomy

Posteriorly, it borders the bony region of the posterior abdominal wall; bulk of the liver lies beneath the right costal margin; anterosuperior surface of the liver fits snugly into the dome of the diaphragm; separated from overlying pleural cavities and pericardium; enclosed by a fibrous capsule known as Glisson’s capsule; portion of the posterior surface of the liver is without a peritoneal covering and is called the bare area and is in direct contact with the diaphragm; right lobe is 13-17cm and left lobe is highly variable (all liver measurements are variable); Homogeneous and moderately echogenic, slightly hyperechoic to normal renal cortex, bile ducts appear as avascular anechoic tubular structures and wont show presence on color doppler

Left Lobe of Liver

Has a lateral and medial segment; is more varied in size; left intersegmental fissure: divides medial and lateral segments along with left hepatic vein, falciform ligament and ligamentum teres are located within this fissure; medial left lobe is also referred to as quadrate lobe

Right Lobe of Liver

Has an anterior and posterior segment; 6x larger than left lobe; right intersegmental fissure divides anterior and posterior segments along with right hepatic vein

Caudate Lobe of Liver

Smallest Lobe; separated from the left hepatic lobe by the proximal portion of the left hepatic vein and the fissure for the ligamentum venosum; lateral margin projects into superior recess of lesser sac (omental bursa); caudal border forms cephalad margin of the epiploic foramen of Winslow (the opening between greater sac and lesser sac); remember greater sac is part of peritoneal cavity and encloses abdominal organs

Liver Division by Hepatic Veins

LHV: divides the medial and lateral left lobes

MHV: separates the left and right lobes

RHV: separates the anterior and posterior segments of the right lobe

H Pattern Lobar Segmentation/Division

Gallbladder: divides the anterior right lobe from the medial aspect of the left lobe

Ligamentum teres: divides the medial and lateral portion of the left lobe

IVC: separates the right lobe from the caudate lobe

Ligamentum venosum: divides the caudate lobe from the lateral left lobe

Hepatic Veins

Increase in size as they drain toward the diaphragm and IVC; triphasic hepatofugal (away from liver) blood flow; indistinct, anechoic borders; course between liver lobes and segments, not through them (this helps to distinguish them from portal veins)

Proper Hepatic Artery (PHA)

Branch of CHA; superior course; divides into right, middle, and left hepatic arteries; cystic artery is a branch of the right hepatic artery; low-resistance blood flow

Portal Veins

Portal system supplies 75% of total blood flow to liver; MPV enters porta hepatis and divides into RPV and LPV; branch further and become intrasegmental (travels between segments); decreases in size as they approach the diaphragm; continuous, monophasic hepatopetal blood flow; echogenic walls due to thick collagenous tissue in the walls

Porta Hepatis

Opening of the liver through which the portal vein and hepatic artery enter and the hepatic ducts exit

Portal triad – common bile duct and hepatic artery course anteriorly to the portal vein at this level, hepatic artery is left lateral to CBD (mickey mouse sign) (portal triads are abundant throughout the liver and are microscopilcally)

Coronary Ligament (registry’s)

Upper layer - extends from superior liver surface to inferior surface of diaphragm

Lower layer – extends from posterior surface of right lobe to right kidney, right adrenal, and IVC

not usually seen on u/s

Right Triangular Ligament (registry’s)

Formed by extension of coronary ligament; connects posterior surface right lobe to right under-surface of diaphragm; not usually seen on u/s

Left Triangular Ligament (registry’s)

Extension of falciform ligament; not usually seen on u/s

Falciform Ligament

Connects liver to anterior abdominal wall and diaphragm; extends from superior surface of liver at umbilical notch to inferior surface at porta hepatis; round ligament (ligamentum teres) is the obliterated umbilical vein, sometimes seen inferior aspect of falciform ligament

Ligament Venosum

Marks anterolateral border of caudate lobe; remnant of fetal ductus venosus

Morisons Pouch

Space between the posterior subphrenic and posterior subhepatic space (between liver and right kidney)

Liver Physiology

Categorized by metabolic, protective, secretory, formative, miscellaneous; liver is: primary center of metabolism, support multiple body systems, digestive and excretory support (metabolizes fats, carbohydrates, and proteins; also forms bile and urea)

Parenchyma

Composed of hepatocytes, interspersed with Kupffer cells, and organized into lobules; approximately 1 million lobules within the liver; portal triads lie peripherally around each lobule

Kupffer Cells

Protects hepatocytes by engulfing toxic or harmful substances

Liver Functions

Metabolic Functions: uptake of body nutrients, such as carbohydrates, amino acids, or proteins, fats, and vitamins; storage site for these substances; metabolic conversion of these substances into nutrients, and subsequent release into blood and bile vessels

Detoxification: protective function; converts harmful substances, such as ammonia, into useful or excretable substances, such as arginine (useful amino acid) and urea (waste product)

Synthesizing: formative function; synthesizes albumin, fibrinogen, prothrombin, and globulins

Additional functions: major source of body heat as a result of hepatocellular chemical reactions

Sonographic Applications

Suspected liver enlargement, hepatic or perihepatic masses, abscesses, obstruction, hypertension, portal or hepatic vein thrombosis, or elevated liver function tests (most common)

Normal Variants

Reidels Lobe: tongue-like inferior extension of the right lobe, as far caudally as the iliac crest; identified when liver tissue extends well below the inferior pole of the right kidney during normal respiration

Distal papillary process of caudate lobe: appears as a rounded prominence on the anteroinferior aspect of the caudate; may be confused with enlarged lymph node or another extrahepatic lesion

Elongated left lobe: extension of the left lobe laterally; may extend all the way to the spleen

Associated Tests