Ultrasound Obstet Gynecol 2010; 36: 93–111
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/uog.7622
The fetal venous system, Part II: ultrasound evaluation
of the fetus with congenital venous system malformation
or developing circulatory compromise
S. YAGEL*#, Z. KIVILEVITCH†#, S. M. COHEN*, D. V. VALSKY*, B. MESSING*, O. SHEN*
and R. ACHIRON‡
*Obstetrics and Gynecology Ultrasound Center, Hadassah-Hebrew University Medical Centers, Mt Scopus, Jerusalem, †Ultrasound Unit,
Negev Medical Center, Macabbi Health Services, Beer Sheba and ‡Ultrasound Unit, Department of Obstetrics and Gynecology, Chaim
Sheba Medical Center, Tel Hashomer and Sackler School of Medicine, Tel Aviv, Israel
K E Y W O R D S: 3D/4DUS; fetal physiology; fetal venous system; IUGR; prenatal diagnosis; venous Doppler; venous
malformations
ABSTRACT
The human fetal venous system is well-recognized as a
target for investigation in cases of circulatory compromise,
and a broad spectrum of malformations affecting this
system has been described. In Part I of this review,
we described the normal embryology, anatomy and
physiology of this system, essential to the understanding
of structural anomalies and the sequential changes
encountered in intrauterine growth restriction and other
developmental disorders. In Part II we review the etiology
and sonographic appearance of malformations of the
human fetal venous system, discuss the pathophysiology
of the system and describe venous Doppler investigation
in the fetus with circulatory compromise. Copyright 
2010 ISUOG. Published by John Wiley & Sons, Ltd.
CONGENITAL ANOMALIES
O F T H E F E T A L V E N O U S S Y S T E M:
ETIOLOGY AND SONOGRAPHIC
APPEARANCE
Abnormal development of the fetal venous system can
stem from any of its four embryonic systems: the
umbilical, vitelline, cardinal and pulmonary systems. We
speculate that the normal developmental course of the
fetal venous system may be disturbed in two ways: (a) by
primary failure of a system or part of a system to form or to
create critical anastomoses, or (b) by secondary occlusion
of an already transformed system. We1,2 have proposed
a classification of fetal venous system anomalies that
expands on the four major embryonic groups mentioned
above.
Classification system of fetal venous system anomalies
A. Cardinal veins
a. Complex malformations: heterotaxy syndromes.
b. Isolated malformations: e.g. persistent left superior
vena cava (PLSVC) or double superior vena cava
(SVC), interrupted inferior vena cava, persistent
left inferior vena cava, double inferior vena cava.
B. Umbilical veins
a. Primary failure to create critical anastomoses:
abnormal connection of umbilical vein (UV) with
agenesis of ductus venosus (DV) (with intra- or
extrahepatic systemic shunt of the UV).
b. Persistent right UV with or without left UV
and/or DV.
c. UV varix.
C. Vitelline veins
a. Primary failure to create critical anastomoses
i. Complete agenesis of portal system (portosystemic shunt)
ii. Partial agenesis of right or left or both portal
branches (portohepatosystemic shunt)
D. Anomalous pulmonary venous connection
a. Total anomalous pulmonary venous connection
b. Partial anomalous pulmonary venous connection
Correspondence to: Prof. S. Yagel, Hadassah University Hospital, Mt Scopus - Obstetrics and Gynecology, PO Box 24035, Jerusalem,
Mt. Scopus 91240, Israel (e-mail: [email protected])
#S.Y. and Z.K. contributed equally to this article.
Accepted: 5 February 2010
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
REVIEW
94
Yagel et al.
Cardinal veins
Heterotaxy syndromes
Heterotaxy syndromes, or incomplete errors of lateralization, involve abnormal placement of some organs due
to a failure to establish normal left–right patterning. It
is important to differentiate these anomalies from complete situs inversus, in which all organs (visceral and
thoracic) are rotated to the opposite side, and which is
usually asymptomatic. Therefore, the first step in evaluating venous system malformations is to determine the fetal
visceral and thoracic situs.
The incidence of heterotaxy syndromes in newborns is
approximately 1 : 10003,4 , and they constitute 2–4% of
all congenital heart diseases (CHD)5 . These syndromes
present in two main forms: asplenia and polysplenia
syndromes. Asplenia is characterized by predominant
right-sidedness and right atrial isomerism, resulting in
a fetus whose left side is a mirror image of its right side.
Congenital heart malformations are frequent (occurring
in 50–100% of cases) and severe and represent the most
important prognostic factors. The most frequent venous
system malformations associated with asplenia include:
PLSVC, anomalous pulmonary venous return and left
sided inferior vena cava (IVC), resulting in a characteristic
juxtaposition of the abdominal aorta and IVC.
Polysplenia is characterized by predominant leftsidedness and left atrial isomerism, resulting in a fetus
whose right side is a mirror image of its left side.
Associated cardiac malformations are rare and less severe
than in asplenia, the most common being atrioventricular
septal defect with complete heart block. The characteristic
venous malformation is an interrupted IVC with azygos
continuation to the SVC. This anomaly arises from a
failure to form the right subcardinal–hepatic anastomosis,
resulting in absence of the hepatic segment of the IVC.
The sonographic landmark is a dilated azygos vein
alongside the aorta on the abdominal circumference
plane and four-chamber view plane, and atrioventricular
block bradycardia. In the sagittal abdominal plane the
descending aorta and azygos vein run side-by-side with
opposite directions of flow (Figure 1).
Interrupted IVC has also been reported as an isolated
entity6 – 10 . In such cases it is usually clinically silent.
Persistent left superior vena cava (PLSVC)
PLSVC is a known variant of venous return observed
in 0.3% of adults without cardiac malformation and in
approximately 4% of adults with CHD11 . Galindo et al.12
found a prevalence of 0.2% in fetuses with normal hearts,
and 9% of fetuses with cardiac anomalies, in a population
referred for echocardiographic examination in a tertiary
center, calculating an odds ratio for CHD of 49.9 for a
fetus with PLSVC.
PLSVC is a remnant of the proximal segment of the
left anterior cardinal vein (LACV), resulting from failure
of the LACV to atrophy following formation of the
oblique anastomosis with the right cardinal vein (the
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
Figure 1 Interrupted inferior vena cava with azygos continuation
imaged in high-definition power flow Doppler (HDPD) (a) and in
B-flow (b). Note the dilated azygos vein (Az) draining into the
superior vena cava (SVC), with flow in the opposite direction to the
flow in the aorta (Ao). Compare with insets showing HDPD and
B-flow images of the normal heart and great vessels. DV, ductus
venosus; LHV, left hepatic vein. (Insets reproduced with permission
from Yagel et al.75 ).
innominate vein) (Figure 2). The vessel most often drains
into the coronary sinus13,14 . It is diagnosed by fetal
echocardiography on observation of a dilated coronary
sinus (though this may not always be present) and an
extraneous vessel identified to the left of the ductal arch in
the three-vessels and trachea (3VT) view of the fetal heart.
In very rare instances, PLSVC may be seen with absent
right SVC15 ; in this case the 3VT view shows three vessels:
the LSVC, ductal arch and aortic arch16 . Multiplanar
Ultrasound Obstet Gynecol 2010; 36: 93–111.
The fetal venous system, Part II
95
Figure 2 Persistent left superior vena cava imaged in gray-scale (a) and with color Doppler (b). In (c) the dilated coronary sinus is visible (CS
and arrows), where the persistent left superior vena cava (LSVC) drains into it. Ao, aorta; MPA, main pulmonary artery; RSVC, right
superior vena cava; Tr, trachea.
reconstruction mode in 4D ultrasound has been shown to
be useful in diagnosis of the PLSVC anomaly17 .
When isolated, PLSVC usually has no clinical significance; however, it has been reported to occur in
isolation in only 9% of cases. It is more often seen in
association with other anomalies: both cardiac (23% of
PLSVC cases), including atrioventricular septal defect,
double-outlet right ventricle, left outflow tract obstructive
anomalies, conotruncal anomalies and ventricular septal
defect, and other extracardiac malformations, including heterotaxy syndrome (41–45%), esophageal atresia,
diaphragmatic hernia, IVC malformations, complex malformation syndromes and chromosomal anomalies. There
may be significant morbidity and mortality, arising from
the associated anomalies rather than the lesion itself12,18 .
Other very rare anomalies of the vena cava have
been reported in the pediatric literature and extensively
reviewed19 .
Umbilical veins
Anomalies of the umbilical and portal veins constitute
the largest group of congenital venous anomalies detected
in-utero. They include three main entities: agenesis of
the DV with extrahepatic umbilicosystemic shunt or with
intrahepatic umbilicohepatic shunt; persistent right UV
(PRUV) with or without intact DV; UV varix.
Agenesis of the ductus venosus
Agenesis of the DV results from failure to form the ‘critical anastomosis’: no connection is established between the
UV and DV, and this in turn leads to shunting of umbilical
blood through an aberrant vessel that may flow either into
extrahepatic veins such as the iliac vein, IVC, SVC, right
atrium20 – 27 or coronary sinus28 , or via an intrahepatic
venous network (umbilicohepatic shunt), through the portal sinus to the hepatic sinusoid (umbilicoportal–hepatic
shunt) or even directly into the right atrium (Figure 3). The
prevalence of the anomaly has been estimated at 6 : 1000
fetal examinations29 . It is often (in 24–65% of cases)
associated with cardiac, extracardiac and chromosomal
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
anomalies, and syndromes such as Noonan syndrome. It
is associated with agenesis of the portal vein in as many as
50% of cases, and may be associated in other cases with
partial or total agenesis of the portal system. Hydrops
and generalized edema occur in 33–52% of cases30,31 ,
and may require postnatal device occlusion29 . DV agenesis presents as an isolated finding in only 35–59% of
cases. In such cases, however, 80–100% have normal
outcome30 – 32 . While only sporadic cases were reported in
neonates before the advent of ultrasound, prenatal sonographic diagnosis of DV agenesis is feasible and many case
series have appeared in the literature2 . Among fetuses with
no or minor associated anomalies, location of the umbilical drainage site seems to impact on prognosis, with a better outcome expected in cases without liver bypass22,31 – 34 .
Jaeggi et al.22 reported 12 cases of agenesis of the DV
with extrahepatic shunt and reviewed a further 17 from
the literature. They reported a mortality rate of 17% from
congestive heart failure in cases with extrahepatic shunt.
Associated malformations were reported in 87% of the
cases, single umbilical artery being the most common.
Berg et al.31 reported 23 cases of agenesis of the DV,
four with extrahepatic drainage and 19 with drainage
of the umbilical vein into the portal sinus. Fifteen of
the 23 fetuses had associated chromosomal or structural
anomalies that impacted outcome. Among the subgroup
of fetuses (8/23) with no or minor associated malformations, outcome was significantly better among those
without liver bypass. They reported a total of 19 cases
with intrahepatic drainage and no or minor associated
anomalies, all of which survived, while only 20/29 with
extrahepatic drainage and no or minor associated anomalies survived. Fetuses with extrahepatic drainage have
a higher risk of congestive heart failure, even in the
absence of cardiovascular anomaly. In reviewing their and
published cases the authors determined that findings of
cardiac malformations, complex non-chromosomal malformation syndromes and hydrops were predictive of
in-utero or neonatal demise, whether drainage was intraor extrahepatic31 .
From our observations we suggest that the parameter
that most influences outcome in cases of agenesis of the
DV is the development of the portal system. We recently
Ultrasound Obstet Gynecol 2010; 36: 93–111.
96
presented data that support the notion that if the shunt
is a narrower, ductus-like connection, some or all of the
portal system will have developed. This in turn impacts
on prognosis35 .
Persistent right umbilical vein (PRUV)
In the course of normal embryonic development, the
right UV degenerates and the left UV is left to carry
blood from the placenta to the fetus. Failure of right UV
involution results in the PRUV anomaly1,36 – 39 (Figure 4).
PRUV is the most frequently detected fetal venous system
anomaly. Its prevalence has been estimated to range
Yagel et al.
from 1 : 250 to 1 : 57037,39 – 42 . It may replace the left
UV, or be found as an intrahepatic supernumerary
vein, connecting to the right portal vein. It may also
bypass the liver, causing aberrant drainage of blood into
the IVC or right atrium40,43,44 . It has been suggested
that primary or secondary occlusion by thromboembolic
events arising from the placenta may lead to early
streaming of blood through the right UV to cause this
anomaly45 . Teratogenic agents such as retinoic acid or
deficient folate induced the PRUV anomaly in rats46 .
Secondary formation of UV anomalies may result from
thromboembolic events occluding the DV or other veins.
Figure 3 (Continued over).
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
Ultrasound Obstet Gynecol 2010; 36: 93–111.
The fetal venous system, Part II
97
Figure 3 (Continued) Variations of agenesis of the ductus venosus (DV).
(a–c) Case of agenesis of the DV with narrow extrahepatic shunt from the
umbilical vein (UV) to the inferior vena cava (IVC), imaged with highdefinition power flow Doppler (HDPD) (a,c) and B-flow (b). In (c) the
appropriately developed portal system is shown. (Az, azygos vein; LHV,
left hepatic vein; LPV, left portal vein; MHV, main hepatic vein; RPVa and
p, anterior and posterior branches of right portal vein; St, stomach.) (d–g)
Complex case of agenesis of the DV with extrahepatic shunt, complicated
with interrupted IVC. (d) HDPD image showing the UV draining into the
shunt, between the IVC and Az. Note the Az is behind the aorta (red)
Int-I, internal iliac vein. (e) B-flow image which helps to demonstrate the
interrupted IVC with Az continuation, and the point of communication
of the UV to the IVC at this connection. Note that there are almost no
blood vessels in the area of the liver, which further suggests agenesis of
the portal system. (f,g) Tomographic ultrasound imaging showing
sequential sagittal planes, confirming the agenesis of the DV and interrupted IVC. The image in (f) is slightly lateral to the left of that in (g).
AoA, aortic arch; dAo, descending aorta; Az, azygos; CT, celiac trunk;
DA, ductus arteriosus; MPA, main pulmonary artery. (h,i) Another case of agenesis of the DV with intrahepatic shunt of the UV to the right
hepatic vein (RHV), imaged in HDPD and B-flow. (j) 4D ultrasound B-flow image of absent DV, with UV drainage to the right atrium (RA).
Ao, aorta; HV, hepatic veins; UC, umbilical cord. (Reproduced with permission from Yagel et al.134.) (k) Agenesis of the DV with partial
agenesis of the portal system. Inversion mode in three-dimensional rendering demonstrating the umbilicoiliac shunt (carets). UA, umbilical
artery. (Reproduced with permission from Achiron et al.55).
Figure 4 Typical appearance of persistent right umbilical vein (UV). (a) The UV is seen passing laterally right of the gall bladder (GB).
(b) The portal vein presents a mirror image of its normal anatomical configuration. The left portal vein (LPV) assumes the right portal vein
(RPV) bifurcation, and its lateral branches change sides, the right side having the inferior (LPVi) and superior (LPVs) branches, and the left
side having only one lateral branch. The ductus venosus (DV) has its origin to the left of the UV axis. (c) The main portal vein (MPV) is
connected to the RPV in a more inferior plane relative to its normal position. LPVm, left portal vein medial branch; ST, stomach; SP, spine;
Ao, aorta.
Echogenic foci situated within the fetal liver suggest this
etiology.
Two of the 74 cases of PRUV reviewed by De Catte
et al. had Noonan syndrome, and one had trisomy 18, all
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
with multiple associated anomalies47 . While early reports
seemed to indicate that PRUV was a worrisome finding
in prenatal ultrasound43,45 , accumulated experience has
shown that in the absence of other anomalies intrahepatic
Ultrasound Obstet Gynecol 2010; 36: 93–111.
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Yagel et al.
PRUV with normal DV connection is usually a normal
anatomical variant with no clinical significance37,39,40,42 .
Ultrasound identification of PRUV is made by visualizing
the aberrant vein passing laterally to the right of the gall
bladder in the plane of measurement of the abdominal
circumference (Figure 4a).
Fetal intra-abdominal umbilical vein varix
Umbilical vein varix is a focal dilatation of vein. It is an
uncommon finding, with an estimated intrauterine incidence of about 1 : 100048 . Most reported UV varices are of
the intra-abdominal UV, but extra-abdominal UV varices
have been reported49 . Fetal intra-abdominal UV (FIUV)
varix is diagnosed when a sonographically anechoic cystic
mass is seen between the abdominal wall and lower liver
edge. Color Doppler ultrasonography helps to distinguish
this vascular anomaly from other cystic lesions in this area
(Figure 5). The diameter of most varices ranges between 8
and 14 mm50 and FIUV varix has been variously defined
as an intra-abdominal UV diameter at least 1.5 times
greater than the diameter of the intrahepatic UV51 , or as
an intra-abdominal UV diameter exceeding 9 mm52 .
In a review of 91 cases, Fung et al.53 reported that
68% presented as an isolated finding, and of these 74%
had a normal outcome. However, 8.1% (5/62) resulted
in intrauterine death in which no specific cause could
be identified and one (1.6%) case had trisomy 21. In
the group with associated sonographic findings, only
27.6% had normal outcome. Congenital abnormalities
and syndromes were confirmed after birth in 20.7%
(6/29), while 27.6% had chromosomal abnormalities.
The overall incidence of aneuploidy was 9.9%, the
majority being trisomy 21 or 18. The incidence of sudden
intrauterine demise was 5.5%, occurring between 29 and
38 weeks of gestation.
The diameter of the UV at first diagnosis and the maximum diameter of the UV over the course of pregnancy
were not found to be related to the occurrence of obstetric complications53 . Diagnosis of FIUV varix warrants a
detailed anatomical search for additional anomalies, karyotyping, echocardiography, and close monitoring of the
fetus for sonographic signs of hemodynamic disturbance.
Fetal heart monitoring is advised from 28 weeks of gestation. The optimal timing for delivery remains the subject
of debate. In light of the apparent high risk of unfavorable outcome, including sudden intrauterine demise even
in isolated FIUV varix, the option of induction of labor
when lung maturity is ascertained may be considered54 .
Vitelline veins
Complete or incomplete agenesis of the portal system
Anomalies of the vitelline veins are extremely rare, and
few cases during fetal life have been reported55 – 59 . Morgan and Superina60 proposed classifying portal agenesis
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
Figure 5 Fetal intra-abdominal umbilical vein (UV) varix: an
anechoic cystic mass (calipers) is seen between the abdominal wall
and the lower liver edge in a longitudinal section (a) and imaged
with high-definition power flow Doppler (b). The varix is shown to
be 1.5 times the diameter of the UV. Bl, bladder.
into two types: Type I, in which there is complete diversion of the portal blood into the vena cava (portosystemic
shunt); and Type II, in which the portal veins are preserved but a portion of portal blood is diverted into the
systemic venous circulation through the liver (portohepatic shunt). Both types were further classified into two
subtypes: Subtype a, in which the splenic vein (SpV) and
superior mesenteric vein (SMV) do not join to form a
confluence, and thus there is no anatomical portal vein;
and Subtype b, in which the SpV and SMV do join to
form a confluence that may shunt to the IVC, renal vein,
iliac vein, azygos vein or right atrium60 .
Complete absence of the portal venous system (CAPVS)
is an extreme example of total failure of the vitelline
veins to transform into the portal system, i.e. there is
primary failure to form the critical anastomosis with the
hepatic sinusoids or UVs (Figures 6 and 7). As a result,
the enterohepatic circulation is disturbed and the portal
venous blood is shunted systemically. Liver development
is supplied by the hepatic arteries. Mesenteric and splenic
venous blood may drain directly into the IVC, renal veins
or hepatic veins, or via the caput medusa to the heart61 .
Associated anomalies are frequent. Northrup et al.62
Ultrasound Obstet Gynecol 2010; 36: 93–111.
The fetal venous system, Part II
99
reported heterotaxy–polysplenia in 25% of their cases,
CHD in 30% (most frequently atrial septal defect and/or
ventricular septal defect) and Goldenhar syndrome in
10%. Achiron et al.55 reported associated malformations,
including trisomy 21, in four of their five cases.
Incomplete absence of the portal venous system
(IAPVS) or partial failure to form critical anastomoses
may represent a more benign form of vitelline vein
abnormality, and may result in agenesis of the right
portal system, with a persistent left vitelline vein connected
directly to the hepatic vein (portohepatic shunt) and an
absent or preserved DV (Figure 8). Neonatal spontaneous
resolution may occur. Achiron et al.55 reported four
cases, none with associated malformations, in three of
which the shunts resolved spontaneously postnatally55 .
Prognosis of IAPVS depends on the presence of associated
malformations and the development of hemodynamic
imbalance with signs of heart failure, cardiomegaly
and hydrops. As opposed to CAPVS, IAPVS is rarely
associated with other malformations, and hemodynamic
compromise depends on the intrahepatic shunt ratio,
leading to IUGR63 .
Hepatic bypass of the portal circulation is known
to cause the so-called hepatic artery buffer effect,
which compensates for the decreased portal supply
by increasing blood flow in the hepatic artery. This
results in a prominent Doppler signal55 , increased blood
flow velocity, and decreased pulsatility index (PI) in
the hepatic artery64 . Long term metabolic sequelae
of portosystemic shunting have been reported in the
postnatal literature and include: hypergalactosemia65 ,
hyperbilirubinemia, hyperammonemia66 , liver masses
including focal nodular hyperplasia, adenoma, hepatoblastoma and hepatocellular carcinoma, and rarely
encephalopathy67,68 .
Anomalous pulmonary venous connection
Anomalous pulmonary venous connection is a group
of rare anomalies that may present in total or
partial form. The combined incidence of anomalous pulmonary venous connection (APVC) has been
reported as 6.8 : 100 000 livebirths69 or 4.9% of all
CHD70 .
Partial anomalous pulmonary venous connection
Figure 6 (a) Tomographic ultrasound imaging (TUI) of the normal
portal system. LPV, left portal vein; MPV, main portal vein; RAPV,
right anterior portal vein; RPPV, right posterior portal vein.
(b) TUI in a case of complete agenesis of the portal venous system.
The arrow indicates the only remnant of the portal system. St,
stomach. (c) High-definition power flow Doppler image of the
sagittal plane showing that the ductus venosus (DV) is present;
thus, the anomaly is not secondary to absent DV in this instance.
The circle indicates the umbilical cord. Ao, aorta; CT, celiac trunk;
IVC, inferior vena cava; LHV, left hepatic vein, UA, umbilical
artery; UV, umbilical vein.
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
Partial anomalous pulmonary venous connection
(PAPVC) is a group of anomalies involving one or more,
but not all, of the pulmonary veins connecting to the
right atrium or a tributary (Figure 9)71 . An atrial septal
defect is often present. There are several variations of this
anomaly70,72 – 74 .
(1) Right pulmonary veins to SVC (Figure 9a): usually
the right upper and middle lung lobes drain into the
SVC and atrial septal defect is present; occasionally
the atrial septum is intact.
Ultrasound Obstet Gynecol 2010; 36: 93–111.
100
Yagel et al.
Figure 7 A case of complete agenesis of the portal venous system. (a) Transverse view of the fetal abdomen showing, beyond the stomach
(St), the spleen (Sp), with the splenic vein coursing towards the right side of the body (blue) to form a confluence with the main portal vein.
Note absence of the afferent intrahepatic venous system and enlarged IVC when compared with the aorta (red, arrow). (b) Pulsed Doppler
insonation of the splenic vein–portal system junction depicting triphasic flow compatible with a systemic venous shunt. (c,d) Venography
performed post-termination. In (c), note the umbilico-IVC shunt (arrow); (d) was taken 1 min later: the splenic vein (long black arrow) is
shown to be confluent with the renal vein (short arrow) and with the superior mesenteric vein (double headed arrow), forming a conduit
(dotted arrow, c) which became enlarged (white arrow) before shunting into the IVC. (Reproduced with permission from Achiron et al.55 ).
(2) Right pulmonary veins to right atrium: veins from all
right lung lobes drain directly into the right atrium,
which can be dilated to as much as twice its normal
size; there is usually an atrial septal defect.
(3) Right pulmonary veins to IVC (Figure 9b): all or some
right lung lobes are drained into the IVC; right lung
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
veins form a characteristic ‘fir-tree’ pattern; the atrial
septum is intact. This variation is often seen with right
lung hypoplasia, bronchial system anomalies, cardiac
dextroposition, right pulmonary artery hypoplasia,
anomalous arterial connection between the aorta and
right lung and other cardiac anomalies.
Ultrasound Obstet Gynecol 2010; 36: 93–111.
The fetal venous system, Part II
101
Echocardiographic diagnosis of PAPVC is made by
visualizing pulmonary veins connecting to the structure
involved; Doppler studies are invaluable in identification
and classification of this group of anomalies, and threedimensional (3D)/4D ultrasound modalities may have
added value in their diagnosis74 – 76 .
Total anomalous pulmonary venous connection
Total anomalous pulmonary venous connection (TAPVC)
involves complete disconnection between the pulmonary
veins and the left atrium (Figure 10)71 . All the pulmonary
veins drain into the right atrium or systemic veins. Onethird of cases present with an associated anomaly, while
two thirds are isolated. TAPVC can be classified into four
types71 :
Type I: anomalous connection at the supracardiac level;
Type II: anomalous connection at the cardiac level;
Type III: anomalous connection at the infracardiac level;
Type IV: connections at two or more of supracardiac,
cardiac and infracardiac levels.
Alternatively, this anomaly can be classed into two
groups:
(1) supradiaphragmatic type: pulmonary veins are connected to: the left innominate vein by the characteristic
vertical vein, or the coronary sinus, the right atrium,
or the SVC, without pulmonary venous obstruction;
(2) infradiaphragmatic type: pulmonary veins drain into
the portal vein or hepatic veins, with pulmonary
venous obstruction.
Figure 8 Incomplete absence of the portal venous system (IAPVS).
Two different forms are shown: (a) absent right portal vein and
portal sinus, showing X-shaped configuration formed by the
umbilical vein (UV), left portal vein (LPV) branches and the ductus
venosus (DV), in the standard transverse plane for abdominal
circumference measurement; (b) dilated aberrant ‘horseshoe
shaped’ arrangement of vessels encircling the right hepatic lobe. Ao,
aorta; IVC, inferior vena cava; LPVi, left portal vein inferior
branch; LPVm, left portal vein medial branch; SP, spine;
St, stomach.
(4) Left pulmonary veins to left innominate vein
(Figure 9c): veins from only the upper left lobe, or
all of the left lung, drain into the left innominate
vein via an anomalous vertical vein; atrial septal
defect is usually present. Left pulmonary drainage
may alternately be to the coronary sinus, IVC, right
SVC, right atrium or left subclavian vein, and may be
associated with cardiac defects or polysplenia/asplenia
or Turner or Noonan syndromes.
(5) Left pulmonary veins to coronary sinus (Figure 9d),
IVC, right SVC, right atrium or left subclavian vein;
very rarely, the right pulmonary veins may connect to
the azygos vein or coronary sinus.
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
There is usually an atrial septal defect. An obstruction
in the pulmonary venous channel will impact the
prognosis of TAPVC. One third of patients have
an associated major anomaly, including cor bilocular,
single ventricle, truncus arteriosus, transposition of the
great arteries, pulmonary atresia, aortic coarctation,
hypoplastic left ventricle, or anomalies of the systemic
veins.
TAPVC should be suspected when pulmonary veins
cannot be visualized entering the left atrium in the
four-chamber apical view plane, with a wide gap
between the posterior wall of the left atrium and the
descending aorta. In the supracardiac type, the right
atrium volume overload causes enlargement of the
atrium and a bowing leftwards of the interatrial septum.
The common pulmonary channel may be visualized
posterior to the left atrium with color Doppler, and
this can be followed to the site of its connection.
The ascending vertical vein to the left innominate vein
can be seen in the 3VT view as an additional vessel
to the left of the pulmonary artery. Doppler studies
show the direction of blood flow in this vessel is
cephalad, opposite to that in the SVC. In the infracardiac
type, the descending vertical vein can be diagnosed
in a transverse plane of the abdomen as an extra
vessel in front of the descending aorta. In the sagittal
Ultrasound Obstet Gynecol 2010; 36: 93–111.
Yagel et al.
102
(a)
(b)
L. Inn. V.
S.V.C.
S.V.C.
R.P.V.
L.P.V.
L.P.V.
R.A.
R.A.
L.A.
C.S.
C.S.
L.A.
I.V.C.
L.V.
R.P.V.
R.V.
R.V.
L.V.
I.V.C.
(c)
(d)
S.V.C.
S.V.C.
V.
L. Inn.
R.P.V.
v.v.
L.P.V.
R.P.V.
L.P.V.
R.A.
C.S.
L.A.
R.A.
C.S.
L.A.
I.V.C.
R.V.
L.V.
I.V.C.
L.V.
R.V.
Figure 9 Common forms of partial anomalous pulmonary venous connection. (a) Anomalous connection of the right pulmonary veins
(R.P.V.) to the superior vena cava (S.V.C.). There is usually a high or sinus venous defect. (b) Anomalous connections of the right
pulmonary veins to the inferior vena cava (I.V.C.). The right lung commonly drains by one pulmonary vein without its usual anatomical
divisions. Parenchymal abnormalities of the right lung are common and the atrial septum is usually intact. (c) Anomalous connection of the
left pulmonary veins (L.P.V.) to the left innominate vein (L. Inn. V.) by way of a vertical vein (v.v.). There may be an additional left-to-right
shunt through the atrial septal defect. (d) Anomalous connection of the L.P.V. to the coronary sinus (C.S.). L.A., left atrium; L.V., left
ventricle; R.A., right atrium; R.V., right ventricle. (Reproduced with permission from Krabill and Lucas71 (Krabill KA, Lucas RV. In Heart
Disease in Infants, Children, and Adolescents (5th edn), Moss AJ, Adams FH, Emmanouilides GC (eds). Williams and Wilkins: Baltimore,
1995; 841–849).)
plane, the vertical vein courses cephalad between the
IVC and the descending aorta, crossing the diaphragm
(Figure 11).
Doppler evaluation is key to the characterization of TAPVC to identify the anomalous connection. Turbulent flow will reveal the location of any
obstruction and the degree of obstruction can be
quantified70 – 72 .
and the development of the pulmonary vascular bed.
Isolated TAPVC, if detected and corrected surgically
early in life, has an excellent outcome. Prognosis is
poor when it is associated with other cardiac lesions
and portal vein obstruction. In cases of TAPVC with
obstruction in the anomalous venous channel, the
neonate usually dies in the first weeks of postnatal
life71,77 .
Prognosis
THE FETAL VENOUS SYSTEM
IN PATHOLOGICAL CONDITIONS
Prognosis in cases of PAPVC and TAPVC is affected by the
presence of any cardiac or extracardiac malformations,
the presence and size of the interatrial connection and any
obstructive lesion in the anomalous connecting vessels,
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
In the physiology section of Part I of this review we
emphasized the unique role of the venous system in
maintaining a positive umbilicocaval pressure gradient.
Ultrasound Obstet Gynecol 2010; 36: 93–111.
The fetal venous system, Part II
S.V.C.
(a)
103
L. Inn. V.
(b)
S.V.C.
v.v.
R.P.V.
C.P.V.
L.P.V.
C.P.V.
R.A.
R.A.
C.S.
L.A.
C.S.
L.A.
L.V.
I.V.C
I.V.C.
R.V.
R.V.
L.V.
(c)
(d)
S.V.C.
S.V.C.
C.P.V.
L.P.V.
R.A.
R.A.
R.P.V.
L.A.
C.S.
C.S.
I.V.C.
I.V.C.
R.V.
L.V.
L.V.
R.V.
I.V.C.
L.H.
R.H.
D.V.
L.P.
R.P.
P.V.
S.V.
S.M.V.
Figure 10 Common forms of total anomalous pulmonary venous connection. (a) Anomalous connection of the pulmonary veins to the left
innominate vein (L. Inn. V.) by way of a vertical vein (V.V.). (b) Anomalous connection to the coronary sinus (C.S.): the pulmonary veins
join to form a confluence designated as the common pulmonary vein (C.P.V.), which connects to the C.S. (c) Anomalous connection to the
right atrium (R.A.). The left and right pulmonary veins (L.P.V. and R.P.V.) usually enter the R.A. separately. (d) Anomalous connection to
the portal vein (P.V.). The pulmonary veins form a confluence, from which an anomalous channel arises. This connects to the P.V., which
communicates with the inferior vena cava (I.V.C.) by way of the ductus venosus (D.V.) or the hepatic sinusoids. L.A., left atrium; L.H., left
hepatic vein; L.P., left portal vein; L.V., left ventricle; R.H., right hepatic vein; R.P., right left portal vein; R.V., right ventricle; S.M.V,
superior mesenteric vein; S.V., splenic vein; S.V.C., superior vena cava. (Reproduced with permission from Krabill and Lucas71 (Krabill KA,
Lucas RV. In Heart Disease in Infants, Children, and Adolescents (5th edn), Moss AJ, Adams FH, Emmanouilides GC (eds). Williams and
Wilkins: Baltimore, 1995; 841–849).)
This assures a low preload index, which is essential for
optimal cardiac drainage. Cardiac output progressively
increases and resistance of the placental vascular bed
decreases while the umbilicocaval pressure gradient
is maintained steady during the third trimester of
pregnancy78 . Any situation hampering this hemodynamic
balance initiates compensatory mechanisms in the arterial
and venous systems. These compensatory mechanisms are
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
gradual and sequential, in correlation with the severity of
the hypoxic insult, hence creating an efficient monitoring
tool of evolving fetal distress.
The most frequent pathological condition affecting the
fetoplacental hemodynamic balance is placental dysfunction. Other etiologies are cardiac (malformations, arrhythmias, or increased preload blood volume) and conditions
resulting in elevation of ventricular end-diastolic pressure,
Ultrasound Obstet Gynecol 2010; 36: 93–111.
104
Yagel et al.
Figure 11 Total anomalous pulmonary venous connection (infracardiac type) imaged in the sagittal plane. Tomographic ultrasound imaging
was applied in post-processing and clearly shows the vertical vein draining into one of the hepatic veins. Ao, aorta; DV, ductus venosus;
LHV, left hepatic vein; VV, vertical vein.
atrial pressure and, consequently, precordial venous pressure. We focus here on uteroplacental insufficiency and
the gradual hemodynamic changes that accompany its
compromised vascular function.
Reduced placental supply to the fetus initiates multiple
compensatory vasodilatory mechanisms involving various
arterial and venous systems. In the arterial system, the
organ most widely studied and clinically evaluated is
the brain (brain-sparing effect)79,80 . Evaluation of various
parts of the arterial circulation in the fetus with circulatory
compromise has been widely performed and reviewed
elsewhere81 – 84 .
The cascade of evolving circulatory compromise
in uteroplacental insufficiency is characterized by hemodynamic changes in the placenta, heart and brain. The
fetal circulation may be viewed as comprising two compartments, with the division at the aortic isthmus: the right
ventricle/placenta, having high resistance, and the left ventricle/brain, having low resistance. The ratio between the
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
resistance indices (RI) of these two compartments has been
used clinically as a monitoring tool of fetal compensatory
mechanisms and the magnitude of hypoxic insult85 – 87 .
The implications for the venous system of these changes
in resistance in the different compartments are four-fold:
reduced blood supply from the placenta to the liver, an
increased proportion (also per unit of weight) of cardiac
output diverted to the fetal body and consequently to
the IVC, increased blood flow through the SVC resulting
from the brain-sparing effect, and an increased afterload
on the right ventricle. These hemodynamic changes lead
to increased preload indices that hamper the supply of
high-quality blood flow from the placenta.
Venous compensatory mechanisms aim to improve the
placental supply to the heart by increasing the proportion
of DV shunting from the portal sinus. Human Doppler
studies have reported variable results. Bellotti et al.88
found that the percentage of UV blood flow shunted
through the DV increased from 26.5% in normally
Ultrasound Obstet Gynecol 2010; 36: 93–111.
The fetal venous system, Part II
grown fetuses to 90.3% in growth-restricted fetuses, with
a consequent increased normalized blood flow volume
from 30.8 mL/min/kg to 41.3 mL/min/kg. Others showed
more moderate changes. Tchirikov et al.89 reported an
increase from 43% to 62%, and Kiserud et al.90 reported
an increase from 25% in normally grown to a mean of
39% in IUGR fetuses. They found that the degree of
shunting in IUGR fetuses is positively correlated with the
severity of placental insufficiency as reflected by the UA
diastolic flow. A significant increase in shunting to the DV
was found only in IUGR fetuses with UA-PI above the
97.5th percentile (35% blood shunted) and in those with
absent/reversed diastolic flow (57% shunted)90 .
Preferential flow through the DV results from reciprocal
hemodynamic changes inside the liver. The presence of a
sphincter in the isthmic portion of the DV has never been
confirmed91 .
Tchirikov et al.92 showed in vitro that rings derived
from portal venous branches developed more force
in reaction to catecholamines than did vascular rings
obtained from the isthmic portion of the DV. In hypoxia,
increased plasma catecholamine levels may evoke an
increase in the DV shunting rate through differential
contraction of the portal venous branches as compared to
the DV. This effect may come into play, in addition to the
active nitric oxide-mediated DV distension, which was
shown experimentally92 . This intrahepatic shift of blood
from the portal system to the DV during hypoxia was
supported by an in-vivo Doppler study. Kessler et al.93
demonstrated that in IUGR fetuses with UA-PI above
the 97.5th percentile, total liver perfusion is decreased
equally to the left and right lobes. However, as placental
insufficiency increased (as measured by the oxygen partial
pressure in the UA), the proportion of left portal vein
(LPV) contribution to the right lobe decreased, being
replaced by increased flow from the main portal vein.
In summary, placental vasculopathy leads to reduced
umbilical flow to the heart. This initiates an intrahepatic
compensatory mechanism, which consists of shifting
blood from the liver to the DV. The liver plays a central
role in regulating fetal growth. Reduced liver perfusion
may provide the first clinical evidence of placental
insufficiency, restricted fetal growth and decreased fetal
weight.
105
of adverse outcome among growth-restricted fetuses
are cardiomegaly, monophasic atrioventricular filling or
holosystolic tricuspid regurgitation, and pulsations in
the UV96 , while among hydropic fetuses they were
UV and DV Doppler94 . This concurs with previous studies showing that in the temporal sequence
of events prior to the appearance of abnormal fetal
heart rate pattern, atonia or fetal demise, the arterial Doppler changes precede those of the venous
system97 but are too early a sign to be used to
time the decision to deliver. This was particularly evident in cases of early-onset IUGR, before 32 weeks of
gestation84,98 .
Adverse perinatal outcome is related to gestational
age at delivery and the degree of placental insufficiency.
Decision-making concerning the time of delivery aims to
strike a balance between fetal injury related to prematurity, and that related to placental insufficiency99 . Results
of the GRIT study100 indicated no significant difference
in terms of stillbirth rate when delivery was immediate.
However, this was refuted by findings at the 2-year follow
up: the rate of cerebral palsy in the immediate delivery
group was as expected (10%), while in the delayed delivery group it was 0%, suggesting that deferred delivery
could be protective management101 . In a prospective multicenter study, Baschat et al.83 found that gestational age
at delivery is the best predictor for intact survival until
29 weeks or 800 g estimated fetal weight, with sensitivities
of 68% and 72%, respectively. Above these thresholds,
DV Doppler parameters were shown to be the primary cardiovascular factor in predicting intact survival, and as such
are the only parameters to use as a trigger for delivery.
Doppler parameters
Early
response
Decreased
fetal growth
Decreased
AFI
Decreased
MPV resistance
DOPPLER STUDIES OF THE FETAL
VENOUS SYSTEM
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
Hypoxia
Increased
UA resistance
Decision point
Doppler investigation is the only non-invasive in-utero
method for assessing fetoplacental hemodynamic status.
Each component of the fetomaternal circulation has
a different role in placental function and fetal wellbeing. Doppler evaluation of the venous system aims
to assess fetal cardiac function, which in severe cases may
deteriorate to an acute event of congestive heart failure.
The cardiovascular profile score94 – 96 combines sonographic markers of fetal cardiovascular status based
on parameters found to be correlated with perinatal mortality. The parameters most strongly predictive
Decreased UV
flow volume
Biophysical parameters
Decreased
fetal movement
Increased
venous pulsation
Decreased
fetal breathing
movements
DV A/RDF
UV pulsations
Late
response
FHR late
decelerations/STV
Acidosis
Reduced
fetal tone
Figure 12 Suggested cascade of fetal circulatory compromise.
Changes in Doppler and physiological parameters follow a
temporal sequence82 . The decision point regards the timing of
delivery. AFI, amniotic fluid index; A/RDF, absent or reversed
diastolic flow; DV, ductus venosus; FHR, fetal heart rate; MPV,
main portal vein; STV, short term variability; UA, umbilical artery;
UV, umbilical vein.
Ultrasound Obstet Gynecol 2010; 36: 93–111.
Yagel et al.
106
Turan et al.82 found a well-ordered sequence of
Doppler abnormalities in placental insufficiency (Figure
12), from early-onset ones, including increased UA
resistance and brain-sparing effect, to late-onset ones, such
as absent/reversed UA diastolic velocity, absent/reversed
DV A-wave, and UV pulsation. The rate of progression
through the sequence correlated significantly with
gestational age: when appearing as early as 26–27 weeks
of gestation, placental insufficiency was usually severe,
progressing from one Doppler abnormality to the next in
approximately 7–10 days. When Doppler abnormalities
emerged near 30 weeks’ gestation, progression intervals
were longer, up to 14 days, and clinically cases were
milder. Doppler changes were limited to the arterial
system, and the median age of delivery was 33 weeks.
These findings, however, were in contrast with those of
Arduini et al.85 , who showed that time intervals between
arterial Doppler changes and delivery for late fetal heart
rate decelerations were statistically significantly longer
when Doppler abnormalities appeared before 29 weeks
of gestation, compared with late-onset cases (mean
interval between Doppler changes and delivery, 13.5
(range, 3–26) vs. 3 (range, 1–9) days. Other studies84,102
have shown that venous Doppler abnormalities preceded
the appearance of late decelerations or reduced shortterm variability (< 2.2 ms) by 6–7 days. In conclusion,
there is a well-documented sequence of biophysical and
Doppler abnormalities that correspond with placental
insufficiency and fetal growth restriction (Figure 12).
Abnormalities in venous system Doppler waveforms are
sensitive tools for the assessment of fetal well-being
before 32 weeks’ gestation, and may help to fine-tune our
decision-making concerning time of delivery in affected
fetuses.
Venous Doppler patterns
Venous Doppler patterns in normal and IUGR fetuses
have been established in large longitudinal and crosssectional studies; normal Doppler patterns were discussed
in Part I of this review. Here we describe Doppler
abnormalities seen in the most commonly investigated
vessels (Figure 13).
Umbilical vein
Umbilical vein Doppler patterns are usually evaluated
in the intra-abdominal portion of the vein. The sample
volume should include the whole cross-section of the
vessel, with an angle of insonation at or as close as possible
to 0◦ . Since the IUGR state includes increased impedance
in the fetoplacental circulation, reduced UV flow volume
and velocity result. However, the considerable overlap
with normal ranges precludes the usefulness of UV flow
velocity as a measure of IUGR103 .
The appearance of pulsatile flow in the UV is a
simple and reliable marker of circulatory compromise,
long recognized as a marker of asphyxia in small-forgestational age fetuses and in cases of non-immune
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
Figure 13 Abnormal Doppler waveforms in the umbilical vein (UV)
(a), ductus venosus (b) and inferior vena cava (IVC) (c).
(a) Abnormal UV waveform in hemodynamically compromised
fetuses is characterized by the appearance of pulsations. (b) The DV
normally has forward blood flow throughout the cardiac cycle. In
compromised fetuses a drop in atrial systolic forward velocities is
observed. As central venous pressure increases, blood flow may be
reversed during atrial systole. (c) Abnormal IVC waveforms in
intrauterine growth restriction show a decrease in forward flow
during the S-wave (S) and D-wave (D) and accentuation of reversed
flow in the A-wave (annotated ‘a’). As the condition deteriorates
the D-wave may be reversed.
hydrops104,105 . Pulsatility in the UV can result from two
main sources of pressure waves: atrial contraction can
cause a sharp deflection (notch) in UV flow, or a wave
from the neighboring arterial flow, which will be traveling
in the same direction, can cause an increment in the UV
flow. The resulting pulsatile UV Doppler pattern may
be only an A-wave notch or, in some severe cases, a
triphasic waveform that mirrors the whole cardiac cycle
may appear103 (Figure 13a).
Ductus venosus
Changes in DV flow are seen in hypoxia and hypovolemia in experimental animal models and in human
fetuses106 – 110 . The DV is sampled at its inlet, with a large
sample volume in a near-sagittal plane, at a low angle of
insonation111,112 . Alternatively, DV flow can be sampled
Ultrasound Obstet Gynecol 2010; 36: 93–111.
The fetal venous system, Part II
in an oblique transverse section of the fetal abdomen.
Normally at 20 weeks’ gestation about 30% of blood is
shunted through the DV, while at 30 weeks about 20%
of blood is shunted103,112 – 114 . In small-for-gestational
age fetuses a much higher proportion of blood is shunted
through the DV, and earlier placental compromise will
show a more pronounced shunt and distension of the
DV103 .
Cardiac events are apparent in the DV waveform.
Reversed or zero flow in the A-wave is a simple sign of
disordered cardiac function. There is reduced velocity in
the A-wave in IUGR, and as the situation worsens it is further deflected owing to increased afterload and preload,
as well as increased end-diastolic pressure, the direct
effects of hypoxia and increased adrenergic drive. Taken
together, these effects produce an augmented atrial contraction and strong deflection during the A-wave in the DV
waveform97,115,116 (Figure 13b). The combination of this
and the DV distension, which lessens wave reflection at
the junction with the UV by lessening the difference in the
vessels’ diameters, produces a considerable effect on UV
flow, and further deterioration leads to decreased velocity
between the systolic and diastolic peaks. These waveform
changes are most apparent in the second trimester and
usually result from chromosomal aberration as opposed
to cardiac decompensation115,117 – 120. Such changes are
rarely observed in the third trimester, when improved
endocrine control operates to attenuate them121 – 123 .
Inferior vena cava
The IVC is usually sampled in the fetal abdomen, caudal to
the hepatic confluence and DV outlet, to avoid interference
from neighboring vessels. Reference ranges for normal
IVC flow parameters have been established124 – 126 . The
IVC is the preferred vessel for postnatal evaluation of
small-for-gestational age neonates and is familiar to
pediatricians, so it is often sampled in the fetus. It is
normal to observe a negative A-wave in the IVC because
of the vessel’s normally relatively low velocities124 – 128 .
In compromised fetuses, an abnormal IVC flow velocity
waveform will show a decrease in forward flow during
the S- and D-waves, and an accentuated reversed flow in
the A-wave (Figure 13c). In severe cases the D-wave may
be reversed.
Hepatic and portal veins
The hepatic vein, while easy to sample, is employed only
infrequently as a parameter in IUGR studies. The signs
of cardiac compromise observed in the hepatic vein are
similar to those apparent in the DV and IVC129,130 .
The left portal vein as the watershed of the fetal venous
circulation. The LPV has been suggested as a simple
marker of circulatory compromise131 – 133 . It is sampled
in the left portal branch between the DV inlet and the
junction with the main portal stem. Disturbed blood flow
in the UA is indicative of increased resistance to blood
flow in the right heart and right liver lobe. Under these
Copyright  2010 ISUOG. Published by John Wiley & Sons, Ltd.
107
pressures, flow in the LPV is reduced and may become pulsatile, bidirectional or reversed. If reversed, oxygen-poor
blood from the spleen and gut will mix with oxygenated
blood from the UV as it courses to the DV, supplying
oxygen-poor blood to the fetal organs. Ultimately during
reversal, more blood could be flowing through the DV
than through the UV that supplies it, possibly creating
suction on the LPV132 . Kilavuz et al.132 showed, in IUGR
fetuses with absent or reversed end-diastolic flow in the
UA, that while UV flow remained normal, LPV flow was
normal in mildly affected fetuses, pulsatile in fetuses with
increased RI or absent flow in the UA, and reversed in
fetuses with reversed flow in the UA. There was a significant correlation between reversed flow in the LPV and
increased RI in the UA.
The normal distribution of blood flow between the
left and right liver lobes is approximately 60%/40%. As
described above, most UV blood (70–80%) perfuses the
fetal liver, while 20–30% is shunted to the DV. Blood
flow in the UV is directed to the left liver lobe and the
DV, with only a minority diverted to the LPV and right
liver lobe. Low or reversed flow in the left portal branch
is an expression of prioritized umbilical perfusion of the
left liver lobe at the expense of the right114 .
CONCLUSION
Congenital malformations of the venous system are a
complex and varied group of lesions. There is much that
we do not know about this system and its anomalies,
but it is clear that knowledge of the embryonic development of affected vessels is key to understanding the
in-utero progress and prognosis of these cases. Whenever
anomalies of the cardinal, vitelline or umbilical system are
diagnosed, they should prompt thorough investigation of
the other segments of the cardiovascular system. It would
appear that anomalies of the venous system are not as
rare as formerly believed, and that more will be diagnosed if practitioners are cognizant of their sonographic
appearance and associated anomalies.
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