AJR 2001; 177:120-122
© American Roentgen Ray Society
Agenesis of the Hepatic Segment of the Inferior Vena Cava with Portal Continuation
Francois Slosman1,2,
Marius R. Schmid1,3 and
Thomas Pfammatter1
1
All authors: Institut für Diagnostische
Radiologie, UniversitätsSpital
Zürich, Rämistr.
100, 8091 Zürich, Switzerland.
2
Present address: University Hospital, Division de
Médecine, Rue Micheli-du-Crest 24, 1211 Geneva
14, Switzerland.
3
Present address : Universitätslinik Balgrist,
Forschstr. 340, 8008 Z
ich, Switzerland.
Received October 16, 2000;
accepted after revision January 9, 2001.
Address correspondence to F. Slosman.
Introduction
The absence of the hepatic segment of the inferior vena cava with azygos
continuation is a well-known congenital anomaly. In this condition, the venous
drainage from the lower extremities and kidneys is shunted into a large azygos
vein that ultimately empties into the superior vena cava. We describe the
incidental finding of a missing hepatic inferior vena cava segment, with
venous return entirely through the liver parenchyma by way of a hilar
cavoportal shunt. A congenital etiology of the abnormality we describe is
supported by the association of these two anatomic variants.
Case Report
A 47-year-old man with a history of coronary disease was admitted because
of severe congestive dilatative cardiomyopathy with an ejection fraction of
less than 20%. He had no history or clinical signs of an inferior vena cava
obstruction. However, during workup for cardiac transplantation, a right-heart
catheterization using the femoral access failed because of an obstructed
inferior vena cava. MR angiography revealed that the hepatic portion of the
inferior vena cava was absent (Figs.
1A,1B,1C,1D)
and suggested the presence of a cavoportal shunt. The venacavogram confirmed
this hypothesis (Fig. 1E). In
the same angiographic run, all three hepatic veins were well depicted after
the hepatic parenchymatous phase (Fig.
1F). The hepatic veins drained into a normal suprahepatic inferior
vena cava. The infrarenal inferior vena cava pressure was 3.5 cm
H2O. The portal venous pressure was 3 cm H2O. Arterial
portographic findings were unremarkable except for an outpouching at the
portal bifurcation corresponding to the cul-de-sac of the inferior vena cava
(Fig. 1G). Arterial portography
showed portal hepatopetal flow. Liver biopsy findings showed evidence of fatty
liver. No fibrotic changes were seen.
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Fig. 1A. —47-year-old man with congestive dilatative cardiomyopathy.
Axial two-dimensional time-of-flight MR images. Four contiguous levels show
agenesis of hepatic portion of inferior vena cava. In retrospect, cavoportal
shunt (arrow, C) is also observable.
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Fig. 1B. —47-year-old man with congestive dilatative cardiomyopathy.
Axial two-dimensional time-of-flight MR images. Four contiguous levels show
agenesis of hepatic portion of inferior vena cava. In retrospect, cavoportal
shunt (arrow, C) is also observable.
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Fig. 1C. —47-year-old man with congestive dilatative cardiomyopathy.
Axial two-dimensional time-of-flight MR images. Four contiguous levels show
agenesis of hepatic portion of inferior vena cava. In retrospect, cavoportal
shunt (arrow, C) is also observable.
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Fig. 1D. —47-year-old man with congestive dilatative cardiomyopathy.
Axial two-dimensional time-of-flight MR images. Four contiguous levels show
agenesis of hepatic portion of inferior vena cava. In retrospect, cavoportal
shunt (arrow, C) is also observable.
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Fig. 1E. —47-year-old man with congestive dilatative cardiomyopathy.
Venacavogram reveals abnormal opacification of portal circulation and absence
of hepatic segment of inferior vena cava. Note missing collateral veins, as
seen in patients with acquired or congenital caval obstruction.
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Fig. 1G. —47-year-old man with congestive dilatative cardiomyopathy.
Superior mesenteric arteriogram obtained during portal phase shows opening to
inferior vena cava (arrow) with side-to-end communication.
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Discussion
To understand the association between a segmental inferior caval agenesis
and a cavoportal shunt, one must consider possible embryonic aberrations of
these singular conditions.
It is generally accepted that the proximal part of the inferior vena cava
is formed by a union between the right subcardinal vein (venous return from
the mesonephroma) and the right hepatocardiac channel (plexus between the
hepatic sinusoids and the heart). The failure of union between these two
vessels results in the so-called absence of the hepatic segment of the
inferior vena cava. In the absence of the inferior vena cava, the right
subcardinal vein fails to make its connection within the liver and shunts its
blood directly into the right supracardinal vein. Therefore, blood from the
lower extremities and abdomen is forced to reach the right heart via the
azygos system and superior vena cava.
Development of a cavoportal shunt may be explained by the fact that the
portal system and the inferior vena cava have common precursors. Connections
between the subcardinal venous system, the vitelline venous system, and the
foregut venous plexus are known to occur during an early stage of embryonic
development [1]. Development of
hepatic vascularization and of the hepatic segment of the inferior vena cava
are closely linked during this stage. The elaboration of hepatic sinusoids is
provoked by the growth of the liver bud into the vitelline plexus. Anterior to
the liver, the paired vitelline veins entering in the corresponding primitive
sinus venosus are called hepatocardiac channels. The right channel is destined
to enlarge and form the hepatic segment of the inferior vena cava. The portal
vein is formed by persisting parts of the right and left vitelline veins and
anastomoses between these two systems. Therefore, it seems reasonable that a
portocaval shunt develops from persisting embryonic vascular remnants of
anastomoses between the different venous plexuses involved in the formation of
both the hepatic segment of the inferior vena cava and the portal vein (e.g.,
the subcardinal and the vitelline venous system).
Examples of portocaval anastomoses are well recognized in patients who have
encephalopathy because the visceral venous return is diverted to the inferior
vena cava. Isolated congenital intrahepatic portocaval shunts have been
reported [2,
3]. Extrahepatic connections
between the portal and caval systems have also been observed in neonates
[4] or in adult patients having
no liver disease [5]. The
association of a congenital mesocaval shunt, azygos continuation of the
inferior vena cava, polysplenia, and dextrocardia, known as the Abernethy
malformation is an extreme variant of a portocaval shunt
[6]. In contrast, rare reports
have described these portocaval anastomoses acting as shunts diverting blood
from systemic to portal venous circulation. Patients with inferior vena cava
interruption and hepatic sinusoids bypassed by a shunt have been reported
infrequently in the literature
[7]. In our patient, the blood
from the inferior vena cava is not only shunted into the portal vein but also
reaches the heart through the liver. To our knowledge, such an anastomosis
associated with absence of the inferior vena cava has not been reported in
humans but is known to occur in animals
[8].
It is highly likely that the cavoportal anomaly in our patient developed
along the same pathway as those in the isolated cases in which there was no
associated absence of the hepatic vena cava. During early embryonic life, the
blood flow follows the shortest way, involving the least resistance, to reach
the right atrium. Because of this, and because of the lack of dilatation of
the azygos system in this stage, the cavoportal shunt in our patient is likely
to have formed before the hepatic segment of the inferior vena cava developed.
It is doubtful that agenesis of the hepatic segment of the inferior vena cava
was a hemodynamic consequence of the cavoportal shunt.
Because of the simultaneous coexistence of these two abnormalities, this
condition could be harmless. Our patient had no risk for portosystemic
encephalopathy or Budd-Chiari syndrome as observed in cases of portocaval
anastomosis or membranous obstruction of inferior vena cava. This patient was
asymptomatic and the discovery of this condition was incidental.
By analogy with the counterpart azygos continuation, the congenital anomaly
reported here might be termed "agenesis of the hepatic portion of the
inferior vena cava with portal continuation" because of the persisting
embryonic collateral pathway via the portal vein.
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Introduction
Case Report
