Download Third sector aberrant vessels of the liver: defenition

GI 11
I MARZOUK MOUSSA, A BEN TEKAYA , A FENNIRA , L BEN FARHAT, N DALI, L
HENDAOUI
MEDICAL IMAGING AND INTERVENTIONNAL DEPARTMENT MONGI SLIM LA
MARSA TUNISIA
Introduction
The third sector is defined by aberrant vessels,
mainly by veins entering directly into the liver
independently of the portal system.
 This contribution is constant, it leads eventually
to localized metabolic changes that create
pitfalls in imaging.
 The purpose of this work is to explain the
pathophysiology of this entity and illustrate
aspects of imaging through two new cases.
Materials and methods
Two patients, aged 62 and 51, were reffered
to our department for an acute intestinal
obstruction for the first and acute
pancreatitis for the second.
An ultrasonography and an abdominal
computed tomography (CT) were performed
for one, a CT scan for the other.
Observation 1
Observation 1
Mrs M.H 51 years old aged woman, without
previous medical history was hospitalized in
surgery for acute pancreatitis.
An abdominal ultrasonography was performed
(Fig. 1), that showed in addition of a gallbladder
lithiasis, a hyperechoic liver steatosis with an illdefined hypoechoic area of segment IV in relation
with an island of "healthy“ liver .
fig. 1: Ultrasound of the liver, gallbladder stones. Hypoechoic area of
segment IV of the liver (arrow) within an overall hyperechoic liver
parenchyma .
Observation 1
Anabdominal CT scan (Fig. 2 and 3) was
performed for the pancreatic grader and has
shown in addition of an edematous pancreas,
an ill-defined area of the segment IV of the liver
that enhanced in the arterial phase of injection
and became isodense to liver parenchyma
in portal time ; realizing a disorder of hepatic
perfusion.
Fig 2a
Fig 2b
Fig. 2 and 3: Axial abdominal CT after
injection of contrast during the arterial
phase (Fig. 2) and portal (Fig. 3): illdefined area of the posterior segment IV of
the liver with enhancement in the arterial
time and which disappeared at the portal
time.
fig3
Observation 1
There was no hepatic tumor mass and no
arterial, venous, or portal vascular hepatic
anomaly.
The semiology of the perfusion disorder was
compatible with the vascularization of segment
IV by an aberrant vessel.
Observation 2
Observation 2
Mr L. H. 62 years old aged man, was hospitalized
for a bowel obstruction. He was operated a year
ago for acute appendicitis.
The questioning and physical examination were in
favor of a high occlusion.
Observation 2
Computed tomography
was performed ,it showed in addition of small
bowel distension, a disorder of hepatic
perfusion of segment IV of the liver as a
parenchymal enhancement during the arterial
phase of injection becomes isodense to the
liver in portal phase.
Fig 4
Fig 5
Fig. 4 and 5: Axial abdominal CT after injection of contrast during the
arterial phase (Fig. 4) and portal (Fig. 5): ill-defined area around
the gallbladder bed (arrow) with enhancement in the arterial time
and which disappeared at the portal time.
Observation 2
There was no hepatic tumor mass and
no arterial, venous, or portal vascular hepatic
anomaly.
The patient was operated and the
occlusion was secondary to a flange.
The semiology of the perfusion disorder was
compatible with the vascularization of
segment IV by an aberrant vessel.
Discussion
Discussion
The liver has the particularity to have a dual
system of arterial and portal input.
 There is in normal state a communication
between these two systems at different anatomical
locations such as liver sinusoids and parabiliary
plexus.
These communication systems are brought into
play physiologically in normal state or in case of
abnormal delivery systems.
Discussion
Some hepatic areas have a third systemic origin
of vascular supply that is done through aberrant
veins , and which enter directly into the liver
independently of the portal system.
These veins anastomose
with the intrahepatic portal system at
various sites and are responsible for a focal
decrease of portal perfusion and a
small increase in arterial supply.
Discussion
These haemodynamic changes are also
responsible for metabolic changes in the
hepatocytes, including lipid metabolism which
may be the cause of healthy liver area in
steatosis or fatty accumulation zones.
 There are mainly three vascular networks: the
Cystic vein to the gallbladder bed, the parabiliary
venous system, the para-umbilical and epigastric
veins.
A single large cystic vein
does not exist . Small venous
channels on the hepatic side
of the gallbladder lead directly
into the liver. Other small
veins flow toward the cystic
duct and merge with channels
from
the
common
bile
duct before terminating in the
portal venous system.
Cystic venous system
Drawing shows the anatomy of the parabiliary venous system.
Diagram shows the anatomy of the paraumbilical vein.
Discussion
 Imaging this third sector is responsible for visible disorders
of hepatic perfusion CT or MRI after injection of contrast by
intravenous way.
 Indeed, the vascularized hepatic parenchyma by these
aberrant veins shows an enhancement more important than
the liver during the arterial time and becomes isodense to
the liver at the portal time.
 Aberrant drainage of the cystic vein in the liver gives the
pseudo- lesions around the gallbladder bed.
Discussion
 Aberrant drainage of the parabiliary venous system causes
artifacts typically localized to the posterior part (dorsum) of
segment IV.
 The epigastric venous system typically provides perfusion
trubles in subcapsular liver areas.
 In some situations this third sector is revealed by rounded or
oval perfusion disorders , making the differential diagnosis
of a tumor almost impossible.
Conclusion
The aberrant vessels are rare and responsible for
most pitfalls in CT image.
The differential diagnosis with a hypervascular
focal liver lesion can be difficult requiring a good
knowledge of their symptomatology.
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