Diagnostic ultrasound ( PDFDrive )

CHAPTER 51 The Pediatric Liver and Spleen 1757
has not been established. Anecdotally, in children with biliary
cirrhosis, portal venous caliber has decreased as cirrhosis
progressed.
he hemodynamic information gleaned from the Doppler
examination usually answers the following questions: Is portal
hypertension present? What is the level of obstruction? What is
the direction of low within the system? Are there portosystemic
collaterals?
Hepatofugal low away from the liver in a portosystemic
collateral vein establishes the diagnosis of portal hypertension.
Clinically, the most important route is through the let gastric
vein, which supplies esophageal varices. he let gastric vein is
rarely visible sonographically in the normal child. When it dilates
to a diameter of greater than 2 to 3 mm, it can be traced from
the splenic vein near the splenomesenteric junction through the
lesser omentum (behind let lobe of liver and anterior to aorta)
to the esophagus. A venous Doppler low pattern makes it possible
to distinguish the vein from the nearby let gastric or hepatic
arteries. Flow direction is determined at the same time. he
caliber of the let gastric vein is usually related to the size of
esophageal varices, and increased diameter is associated with
increased risk of bleeding. 72
he paraumbilical vein classically shunts blood from the let
portal vein to the periumbilical venous network. It follows a
vertical, right paramedian course to enter the falciform ligament
through the let lobe of the liver 73,74 (Fig. 51.28). With a highfrequency
transducer (7.5-10 MHz), its subcutaneous course is
easily seen on sonography from the lower tip of the let lobe of
the liver to the umbilicus. Other spontaneous portosystemic
collateral veins should be sought near the spleen, let kidney,
and lanks, where splenorenal shunts (Fig. 51.29) or dilated
perirenal, retroperitoneal, or gonadal veins receive blood from
the splenic or mesenteric veins; in the pelvis (Fig. 51.30), around
the right kidney; and near the porta hepatis and gallbladder
(Fig. 51.31, Video 51.10), where portocaval, paraduodenorenal,
or veins of Sappey may shunt the blood between portal and
hepatic veins. he variety of spontaneous portosystemic collaterals
is almost limitless.
All portosystemic collaterals should be traced to their recipient
systemic vein, which is usually dilated where the shunt enters.
he “donor” splanchnic vein is also dilated. When portal hypertension
decreases ater shunt surgery or transplantation, portosystemic
collaterals decrease in size (as do the enlarged spleen and
lesser omentum).
If a spontaneous or surgical portosystemic shunt is large,
hepatic encephalopathy may ensue. he Doppler examination,
being “physiologic,” may reveal unusual portosystemic collateral
routes diicult to demonstrate with arterioportographic studies
(locally inverted low in intrahepatic portal venous branches,
“neo” veins leading from portal veins to abdominal wall, or
hepatofugal low in splenic vein).
Prehepatic Portal Hypertension
Prehepatic portal hypertension results from obstruction of the
splenic, mesenteric, or portal vein. As with other venous thromboses,
predisposing factors involve the vessel wall (trauma,
catheters), stagnant blood low, and abnormal clotting factors.
Principal causes of thrombosis of the portal vein include (1)
trauma such as umbilical venous catheterization; (2) dehydration
or shock; (3) pyophlebitis following appendicitis or abdominal
sepsis; (4) coagulopathy, with protein C deiciency increasingly
recognized; (5) portal vein invasion by adjacent tumors; (6)
compression of the vein by pancreatitis, lymph nodes, or tumor;
and (7) increased resistance to portal venous low into the liver
in cirrhosis or the Budd-Chiari syndrome.
Recanalization of portal venous thrombi usually occurs rapidly
in children. In addition, paraportal venous channels and the
cystic veins draining the gallbladder dilate and channel blood
into the liver if there is no obstruction at this site (in cirrhosis
or hepatic vein thrombosis). he resultant collection of tortuous
veins is called cavernous transformation of the portal vein or
a cavernoma (see Fig. 51.31). Hepatopetal low toward the liver
in these vessels is easily detected with Doppler sonography. Despite
these collateral channels, portal hypertension follows, oten with
esophageal varices. 75
Causes of Portal Vein Thrombosis
Trauma
Catheters
Dehydration
Shock
Pyelophlebitis
Coagulopathy, especially protein C deiciency
Portal vein invasion
Portal vein compression
Cirrhosis
Budd-Chiari syndrome
Ater thrombosis of the portal vein, the peripheral intrahepatic
portal veins become small and threadlike. he lumen of portal
branches may not be visible. Careful examination of these vessels
with Doppler sonography usually shows hepatopetal venous low,
likely the result of shunting through the vessels at the porta
hepatis, which constitute the “cavernoma.” Because the obstruction
to venous low occurs at the porta hepatis, it is not surprising
that children with portal venous thrombosis do not have enlarged
paraumbilical veins and a caput medusa; this portosystemic route
relies on abundant low in the let portal vein. 75
Another cause of prehepatic (or intrahepatic “presinusoidal”)
portal hypertension in children is congenital hepatic ibrosis
(Fig. 51.32). his autosomal recessive disease is characterized
by ibrosis at the portal triad, where terminal branches of the
portal vein and small bile ducts are compressed. Hepatocytes
and liver function are normal. 10 Liver architecture is disturbed
by linear or cystlike structures representing variable bile duct
ectasia, as well as paraportal collaterals (cavernoma). 76,77 hese
children usually have bleeding esophageal varices. Sonography
shows hallmarks of portal hypertension: splenomegaly and a
thick lesser omentum in which a dilated tortuous let gastric
vein may be visible, with hepatofugal low detected with Doppler
sonography. Congenital hepatic ibrosis is usually associated with