Page 354 - Libro 2

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PART 5 — ABDOMINAL
Liver
LPV
PV
CV
Stomach
RPV
Spleen
Small intestine
SMV
SV
IMV
(RPV).3 The portal veins then branch into medial and lateral divisions on the left, and anterior and posterior divisions on the right. Portal veins contain no valves and have bright echogenic walls due to thick collag- enous tissue. They course within the liver segments (intrasegmental) and emanate from the porta hepatis.
HEPATIC VEINS
Hepatic veins are anatomically separate from the por- tal venous system. Unlike the portal veins, hepatic veins are thin-walled structures that run between the lobes of the liver (intersegmental) and increase in caliber as they approach the diaphragm. Three main hepatic veins (right, middle, and left) provide the pri- mary outflow route of blood from the liver. They drain into the IVC close to the right atrium and contain no valves.2 The right hepatic vein (RHV) is usually the largest. In 96% of individuals, the middle hepatic vein (MHV) and left hepatic vein (LHV) join to form a common trunk before entering the IVC. Accessory hepatic veins are common, but are seldom identified sonographically. Of note, the caudate lobe of the liver drains directly into the IVC with the caudate vein being the largest draining vein of this lobe.4 This is
important in the presence of venous outflow diseases, which will be discussed later in the chapter.
HEPATIC ARTERY
The hepatic artery branches off the celiac trunk to the right. At this level, the hepatic artery is known as the common hepatic artery. It continues over the anterior superior edge of the pancreas where it gives rise to the gastroduodenal artery. At this point, the common hepatic artery becomes the proper hepatic artery, terminating at the porta hepatis giving off right and left branches. In the majority of patients, the he- patic artery lies anteromedial to the portal vein. The hepatic artery branches accompany the portal veins.
SONOGRAPHIC EXAMINATION TECHNIQUES
There are various indications for hepatoportal du- plex ultrasound. Table 22-1 lists several indications for hepatoportal scanning. Any of these conditions can alter the blood flow patterns within the inflow and outflow vessels in the liver.
Large intestine
Figure 22-1 A diagram illustrating the normal portal vas- cular anatomy. The red arrows depict normal direction of blood flow. PV, portal vein; RPV, right portal vein; LPV, left portal vein; CV, coronary vein; IMV, inferior mesenteric vein; SMV, superior mesenteric vein; SV, splenic vein.