AJR 2000; 175:153-157
© American Roentgen Ray Society
Transhepatic Portosystemic Shunts
CT Appearance and Anatomic Correlation
Kenji Ibukuro1,
Toshitaka Tsukiyama,
Koichi Mori and
Yoshihiro Inoue
1
All authors: Department of Radiology, Mitsui Memorial Hospital, 1-Kanda
Izumicho Chiyoda-ku, Tokyo 101-8643, Japan.
Received August 23, 1999;
accepted after revision November 1, 1999.
Address correspondence to K. Ibukuro.
Introduction
Portosystemic shunts, which develop in patients with portal hypertension,
are classified as two types based on their location: extrahepatic
portosystemic shunts and transhepatic portosystemic shunts. The extrahepatic
portosystemic shunts are well known and include esophageal varices and
splenorenal shunts. Except for descriptions of the paraumbilical vein, little
information has been published in imaging literature regarding the CT
appearance of transhepatic portosystemic shunts.
In 1883, Sappey [1]
described the accessory portal veins in the suspensory ligament, such as the
vessels located at the falciform ligament through which the anterior parietal
veins communicate with the left branch of the portal vein. These vessels play
a role in the origin of transhepatic portosystemic shunts.
CT during arterial portography (CTAP) can selectively opacify the portal
venous system and show tiny portosystemic shunts outside the liver such as the
veins of Retzius [2]. In this
pictorial essay, we describe the transhepatic portosystemic shunts classified
by anatomic location mainly on the basis of the CTAP appearance.
Classification
Transhepatic portosystemic shunts are classified as two types on the basis
of the draining vein. In the hepatic venous type, the intrahepatic portal vein
communicates with the hepatic vein in or on the surface of the liver; in the
systemic venous type, the intrahepatic portal vein runs toward the outside of
the liver and communicates with the systemic veins.
Hepatic Venous Type
Intrahepatic Type
In the intrahepatic type, the portal vein communicates with the hepatic
vein in the liver through a dilated venous aneurysm
[3] (Fig.
1A,1B).
Dynamic CT reveals the dilated portal branch running into the venous aneurysm
and early venous draining of the hepatic vein. The communication is usually
single and rarely multiple. Yoshimitsu et al.
[4] reported multiple
intrahepatic portosystemic shunts in a patient with hepatic encephalopathy who
was treated by transhepatic embolization of the shunts.
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Fig. 1A. —Hepatic venous (intrahepatic) type of transhepatic portosystemic
shunt in 59-year-old man with liver cirrhosis. Contrast-enhanced axial CT scan
shows large venous aneurysm (arrowheads) and early venous drainage
into right hepatic vein (thick arrow). Note middle hepatic vein
(thin arrow) is not opacified.
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Fig. 1B. —Hepatic venous (intrahepatic) type of transhepatic portosystemic
shunt in 59-year-old man with liver cirrhosis. CT scan obtained 1 cm below
A shows dilated right portal vein (arrow) and large venous
aneurysm.
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Surface Type
In the surface type, the portal veins communicate with the hepatic vein,
not in the liver, but on the surface of the liver (Fig.
2A,2B,2C).
Both portal and hepatic veins are dilated. Sheporaitis and Freeny
[5] recently described hepatic
and portal surface veins and found that no apparent portohepatic shunt was
present in these veins. However, it is not easy to diagnose the lack of a
shunt between these veins only on the basis of contrast-enhanced CT. We
believe CTAP is one of the best techniques to show a tiny portosystemic shunt
on the surface of the liver. Unless the continuity of the portal and hepatic
veins is pursued, especially on CTAP with a helical scan, a tiny shunt could
be misdiagnosed as a small hemangioma.
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Fig. 2A. —Hepatic venous (surface) type of transhepatic portosystemic shunt in
75-year-old man with liver cirrhosis. CT during arterial portography (CTAP)
image shows dilated left lateral portal vein (arrowheads) running
toward anterior surface of liver.
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Fig. 2B. —Hepatic venous (surface) type of transhepatic portosystemic shunt in
75-year-old man with liver cirrhosis. CTAP image obtained 1 cm below A
shows shunt (white arrow) between portal vein (arrowhead)
and peripheral branch of left hepatic vein (black arrow).
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Fig. 2C. —Hepatic venous (surface) type of transhepatic portosystemic shunt in
75-year-old man with liver cirrhosis. Shaded surface—display image shows
dilated left lateral portal vein (thin arrow), shunt
(arrowheads), and left hepatic vein (thick arrow).
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Systemic Venous Type
Falciform Ligament Type (Umbilical or Paraumbilical Vein Type)
The falciform ligament type of vein is the best known of the various
transhepatic portosystemic shunts and is called the inferior vein of Sappey.
The umbilical and paraumbilical veins run left anteroinferiorly from the
umbilical point or the peripheral left medial portal vein through the round
ligament or the falciform ligament, respectively. The veins communicate with
the superior or inferior epigastric veins in the rectus abdominis muscle or
with the thoracoepigastric veins in the subcutaneous tissue and finally drain
into the internal thoracic veins or iliac veins. Disagreement is found over
whether the obliterated umbilical vein can be recanalized
[6]; however, as we show, two
distinctly different veins exist. The umbilical vein is the vein from the
umbilical point of the left portal vein presenting as the opacified round
ligament on CTAP (Fig. 3); the
paraumbilical veins are the vessels from the peripheral left medial portal
vein running toward the surface of the liver, the falciform ligament, and
anterior abdominal wall (Fig.
4A,4B).
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Fig. 3. —Paraumbilical and umbilical veins in 62-year-old man with liver
cirrhosis. CT during arterial portography image shows dilated left medial
portal vein (arrowhead), which represents origin of paraumbilical
vein, running toward surface of liver. Note small dot (arrow) with
enhancement identical to round ligament representing recanalized umbilical
vein.
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Fig. 4A. —Paraumbilical vein in 72-year-old woman with liver cirrhosis. CT
during arterial portography (CTAP) image shows dilated left medial portal vein
(black arrow), which is origin of paraumbilical vein. Note round
ligament (white arrow) is not opacified.
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Fig. 4B. —Paraumbilical vein in 72-year-old woman with liver cirrhosis. CTAP
image obtained 1 cm below A shows opacified paraumbilical vein located
at falciform ligament (arrowheads) and unopacified round ligament
(arrow).
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In a cadaver, the paraumbilical veins are located in the falciform ligament
superior to the round ligament, unite with each other, and enter the surface
of the medial segment of the left lobe. When the liver parenchyma around the
vein is removed, the communication between the paraumbilical vein and the
peripheral branch of the left medial portal vein is identified. The proximal
portion of the umbilical vein, called the Rest-Kanal of Baumgarten
[6], is dissected; then the
fenestration between the umbilical vein and the left portal vein is shown.
Apex Type
The vein arising from the peripheral branch of the left medial portal vein
runs toward the apex of the liver and drains into the internal thoracic vein
(Fig. 5). The vein is called
the superior vein of Sappey. Although the origin of the vein is the same as
that of the paraumbilical vein, this type of vein is rarely seen. This pathway
is also important in explaining the liver "hot" spot
[7] that is sometimes shown in
patients with superior vena cava syndrome
(Fig. 6). Contrast medium or
isotopes injected into the arm go into the liver through the internal thoracic
veins and this shunt. In a cadaver, both the artery and the vein arising from
the internal thoracic artery and vein run through the diaphragm and reach the
apex of the liver.
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Fig. 5. —Apex type transhepatic portosystemic shunt in 56-year-old woman with
liver cirrhosis. CT during arterial portography image shows opacified vessel
(black arrow) from surface of medial segment of left lobe running
toward left anteriorly. This vein communicates with left internal thoracic
vein (white arrow).
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Fig. 6. —Liver "hot" spot in 48-year-old man with superior vena
cava obstruction caused by mediastinal tumor. Contrast-enhanced axial CT scan
shows opacity of medial segment of left lobe (arrowheads) supplied by
left internal thoracic vein (arrow). Note direction of blood flow in
shunt is opposite to that of portal hypertension in
Figure 5.
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Right Posterior Portal Vein Type
The right posterior portal vein type is well recognized next to the
paraumbilical vein type. The dilated right posterior portal vein runs across
the posterior surface of the liver, takes a tortuous course, forms a venous
aneurysm outside the liver, then drains into the inferior vena cava directly
or through the adrenal vein [8]
(Fig.
7A,7B).
The venous aneurysm is located at the adrenal gland and may present as an
adrenal pseudotumor. The orifice of the shunt is narrow; therefore, it is
difficult to recognize the shunt between the venous aneurysm and the inferior
vena cava. However, CTAP can show this shunt. The dilated vein arises not only
from the posterior branch of the right portal vein but also from the posterior
surface of the right portal vein.
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Fig. 7A. —Right posterior portal vein type transhepatic portosystemic shunt in
67-year-old man with liver cirrhosis and hepatocellular carcinoma. CT during
arterial portography (CTAP) image shows opacity (arrow) in inferior
vena cava, which proves that portosystemic shunt is between right posterior
portal vein and inferior vena cava. Large portal perfusion defect (L) is noted
indicating hepatocellular carcinoma.
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Fig. 7B. —Right posterior portal vein type transhepatic portosystemic shunt in
67-year-old man with liver cirrhosis and hepatocellular carcinoma. CTAP image
obtained 1 cm below A shows dilated right posterior portal vein
(arrow) running toward surface of liver and dilated vein
(arrowheads) outside liver.
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Bare Area Type
In the bare area type, the vein is not as dilated as the right posterior
portal vein type described previously; however, the peripheral branch of the
right posterior portal vein runs across the surface of the liver and drains
into the intercostal vein or the right inferior phrenic vein (Fig.
8A,8B).
The intercostal or phrenic arteries supply the hepatic tumor through the bare
area especially in patients with celiac artery obstruction.
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Fig. 8A. —Bare area type transhepatic portosystemic shunt in 84-year-old woman
with liver cirrhosis. CT during arterial portography (CTAP) image shows
peripheral right posterior portal vein (arrow) and opacified right
inferior phrenic veins (arrowheads) at posterior surface of
diaphragm.
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Left Triangular Ligament Type
A shunt is seen between the peripheral branch of the left lateral portal
vein and the left inferior phrenic veins at the left triangular ligament.
Therefore, the left intercostal veins, left pericardiacophrenic veins, and the
left inferior phrenic vein draining into the inferior vena cava or the left
renal vein can be opacified on CTAP (Figs.
9 and
10A,10B,10C).
In a cadaver, the peripheral portal triads of the left lobe of the liver and
the left hepatic vein run toward the left triangular ligament. These vessels
become fibrous in the left triangular ligament and adhere to the posterior
surface of the diaphragm.
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Fig. 9. —Left triangular ligament type transhepatic portosystemic shunt in
57-year-old man with liver cirrhosis. Contrast-enhanced axial CT scan shows
dilated left lateral posterior portal vein (arrowheads) extending
beyond liver parenchyma and anastomosing left inferior phrenic vein
(arrow) under left hemidiaphragm. Left pericardiacophrenic vein is
opacified (not shown) on CT scan obtained 3 cm above this axial image.
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Fig. 10A. —Left triangular ligament type transhepatic portosystemic shunt in
72-year-old woman with liver cirrhosis. CT during arterial portography (CTAP)
image shows peripheral left lateral posterior portal vein (arrow) and
left inferior phrenic vein (arrowhead) at apex of left lobe.
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Fig. 10B. —Left triangular ligament type transhepatic portosystemic shunt in
72-year-old woman with liver cirrhosis. CTAP image obtained 2 cm below
A shows left lateral posterior portal vein (black arrow) and
tubular structure that is left inferior phrenic vein (white
arrow).
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Fig. 10C. —Left triangular ligament type transhepatic portosystemic shunt in
72-year-old woman with liver cirrhosis. CTAP image obtained 3 cm below
B shows small dots (arrow) adjacent to crus of left
hemidiaphragm indicating left inferior phrenic vein running into left renal
vein.
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Clinical Significance
Transhepatic portosystemic shunts play a role as collateral vessels in
patients with portal hypertension and superior vena cava syndrome. Such shunts
may result in hepatic encephalopathy even in patients without liver cirrhosis.
The hepatic venous type of shunt may mimic a hemangioma or aneurysm in the
liver on conventional contrast-enhanced CT. This uncertainty necessitates
helical CT or color Doppler sonography for precise diagnosis. The shunts can
cause nontumoral defects of portal perfusion adjacent to the falciform
ligament on CTAP.
Conclusion
Although transhepatic portosystemic shunts (except for the paraumbilical
vein) are rarely noticed on CT, the location of the shunts is mainly related
to the suspensory ligaments of the liver, such as the falciform ligament and
the right and left triangular ligaments. These shunts can occur even in the
absence of underlying liver disease. Their presence alone should not
automatically lead one to initiate an investigation looking for liver disease
as a cause.
Acknowledgments
We thank Jan E. Oda-Biro for manuscript preparation.
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Introduction
Classification
