human venous system

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The Human Fetal Venous SystemNormal Embryologic, Anatomic, and

Physiologic Characteristics andDevelopmental Abnormalities

Sozos J. Fasouliotis, MD, Reuven Achiron, MD,Zvi Kivilevitch, MD, Simcha Yagel, MD

Objective. The introduction of high-resolution ultrasonography combined with color-coded Doppler

imaging offered a breakthrough in the evaluation of the human fetal venous system, considerablyenhancing our understanding of fetal venous circulation in normal physiologic conditions, as well as

providing us the ability to study circulatory changes in abnormal circumstances. The purpose of this

study was to describe the normal anatomic development and complex of anomalies of the human

fetal venous system and to review recently published series of these anomalies. Methods. Normal

embryologic and anatomic development is described. An English language literature search of recent

MEDLINE listings was performed to glean data from recently published series reporting prenatal diag-

nosis of the various anomalies and their associated malformations. Results. Anomalies of the human

fetal venous system occur sporadically, often associated with cardiac or other malformations. The

pathophysiologic mechanisms leading to abnormal in utero development of the human venous sys-

tem remain largely undetermined. On the basis of the type of vein involved, embryologic precursor,

and etiologic correlation (primary or secondary), classification into 4 major groups is described.

Conclusions. Prenatal evaluation of fetuses found to have anomalies of the venous system shouldinclude a careful search for cardiac anomalies, including pulmonary venous drainage, and a detailed

anatomic survey of the umbilical, portal, hepatic, and ductal systems to determine aberrant commu-

nication and, if possible, to discover clues to systemic diseases or thromboembolic phenomena. Key

words: anomalies; fetal venous system; prenatal diagnosis.

Received March 28, 2002, from the Department of

Obstetrics and Gynecology, Hadassah UniversityHospital, Ein Kerem, Jerusalem, Israel (S.J.F.);Department of Obstetrics and Gynecology, ShebaMedical Center, Tel Hashomer, Jerusalem, Israel(R.A.); Macabbi Health Services, UltrasoundCenter, Beer Sheba, Israel (Z.K.); and Departmentof Obstetrics and Gynecology, Hadassah UniversityHospital, Mount Scopus, Jerusalem, Israel (S.Y.).Revision requested April 9, 2002. Revised manu-

script accepted for publication July 1, 2002.Address correspondence and reprint requests

to Simcha Yagel, MD, Department of Obstetricsand Gynecology, Hadassah University Hospital,Mount Scopus, PO Box 24035, Mount Scopus,

Jerusalem, Israel.

AbbreviationsPAPVC, partial anomalous pulmonary venous connec-tion; TAPVC, total anomalous pulmonary venous con-nection

ecent developments in ultrasonographicimaging, including the development of high-resolution ultrasonography combined withcolor-coded Doppler imaging, facilitate pre-

natal diagnosis of fetal malformations of varyingseverity. This in turn enables caregivers to provide aprognosis to the parents depending on the malforma-tion detected. Furthermore, prenatal diagnosis of fetalmalformations, especially of the heart, has been foundto improve morbidity and mortality rates during post-natal treatment.13

Although the fetal venous system was describedalmost 20 years ago,4,5 it was the introduction of high-resolution ultrasonography combined with color-coded Doppler imaging that offered a breakthrough inthe evaluation of this system,68 considerably enhanc-

2002 by the American Institute of Ultrasound in Medicine J Ultrasound Med 21:11451158, 2002 0278-4297/02/$3.50

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ing our understanding of fetal venous circula-tion in normal physiologic conditions as well asproviding us the ability to study circulatorychanges in abnormal circumstances. Never-theless, the pathophysiologic mechanisms lead-ing to in utero abnormal development remainlargely undetermined.6

The most commonly reported abnormalitiesinvolve the intrahepatic umbilical vein, but rarecases of agenesis of the ductus venosus have alsobeen reported.916 Improvement in imaging tech-nology led to a search for the in utero diagnosis ofother rare anomalies of the fetal venous inlet sys-tem.1320 Two recent relatively large series describ-ing fetal venous system malformations suggestedthat in a targeted fetal organ scan, the course ofthe umbilical vein, ductus venosus, portal and

hepatic veins, inferior vena cava, and pulmonaryveins, as well as associated anomalies, can beclearly visualized and accurately diagnosed withthe use of two-dimensional gray scale and colorDoppler imaging.16,18

The only information currently availableregarding the etiology, importance, and progno-sis of these abnormalities is derived fromneonates1921; however, fetal outcome cannot beextrapolated from data obtained from neonateswith similar abnormalities. As the number ofcase reports regarding various fetal vein abnor-

malities increases,14,2224

prenatal treatment ofthese patients may become problematic, andunderstanding the embryologic basis and patho-physiologic mechanisms of fetal venous inletsystem abnormalities becomes increasinglyimportant for accurate prenatal counseling.

In this review we provide a detailed descriptionof the embryologic, anatomic, and physiologiccharacteristics of the normal human fetal venoussystem. In addition, we describe a classificationsystem of associated developmental abnormali-ties of this system based on the type of veininvolved.

Normal Development of the Human FetalVenous System

Embryologic CharacteristicsA system of 3 paired veins is found in the 4-weekembryo, which includes the umbilical veins fromthe chorion, the vitelline veins from the yolk sac,and the cardinal veins from the body of theembryo itself, all of which open to the right andleft horns of the sinus venosus of the heart. Any

further development of the fetal venous systemrepresents changes occurring in these symmetricvenous systems (Fig. 1A).

The fetal liver and its development in the sep-tum transversus play an important role in modi-fying the primitive vitelline and umbilical systemsinto their final shape. First the developing hepat-ic sinusoids link to both vitelline veins and thentap the umbilical vein at day 32. Each vitellinevein is then interrupted by the sinusoidallabyrinth to a distal segment extending from theyolk sac to the liver, which is finally converted intothe portal vein and to a proximal segment extend-ing from the liver to the heart, in which the rightproximal stem represents the hepatic vein,whereas the left proximal and right distal vitellineveins atrophy and disappear (Fig. 1B).

The umbilical veins also undergo severalchanges. In the 5-mm embryo, the left umbilicalvein becomes the dominant conduit of bloodfrom the placenta, emptying into the left horn ofthe sinus venosus. Laterally expanding primitiveleft and right lobes of the liver contact the pairedumbilical veins coursing close by, thus formingan anastomotic system among liver sinusoids,vitelline veins, and umbilical veins, causing theloss of connection between both umbilical veinswith the fetal heart. Eventually, in the 6-mmembryo, the entire right umbilical vein and prox-

imal segment of the left umbilical vein atrophyand soon disappear. Thus all placental bloodenters the right atrium through the left distalumbilical vein, ductus venosus, and proximalright vitelline vein, which bypass the liver sinu-soids. As development continues, in the 9-mmembryo, the left and right portal veins are alreadypart of the left umbilical vein, whereas the hepat-ic vein and ductus venosus drain into the infra-cardiac portion of the inferior vena cava (Fig. 1C).

The cardinal veins form the main venousdrainage system of the embryo body, with theanterior and posterior cardinal veins draining theembryonic cranial and caudal parts of the body,respectively, which then empty into a commoncardinal vein, which is the third venous systementering the sinus venosus of the primitive heart.The left brachiocephalic vein is formed duringthe eighth week from the right anterior and rightcommon cardinal veins, through left-to-rightanastomosis, whereas the left anterior cardinalvein disappears. After the atrophy of the posteri-or cardinal veins, the subcardinal and supracar-dinal veins are formed. The latter, after division

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in the renal area, form the azygos and hemi-azygos veins above this level, whereas below thislevel the left supracardinal vein degenerates,and the right supracardinal vein becomes thecaudal part of the inferior vena cava. The uppersegments of the inferior vena cava are derivedfrom the subsupracardinal anastomosis at therenal area, the prerenal segment from the rightsubcardinal vein, and the hepatic segment fromthe proximal vitelline vein and the liver sinu-soids.

The common pulmonary vein can be identi-fied in a 4-mm embryo as an invagination of thedorsal wall of the left atrium. As the atrial cavitydevelops, the stem of the pulmonary vein isgradually incorporated into the left atrial wall,until finally the 2 right and left branches of the

pulmonary stem enter the atrial cavity. In thehuman embryonic venous system, the leftumbilical vein eventually remains the only veinfrom the placenta to the fetal heart, and thedevelopment of its connection and the ductusvenosus (the critical anastomosis) is of pri-mary importance in the development of thevenous drainage system and supply of oxygenat-ed blood to the fetus. The ductus venosus isunique to fetal life, arising from the vitelline veinwithin the liver (hepatic sinusoids). From thisvessel arise the portal vein, the superior mesen-

teric vein, and the intrathoracic inferior venacava, which joins the ductus venosus to theheart (the hepatocardiac portion; Fig. 1C).

Anatomic CharacteristicsBy the end of the first trimester, the umbilicalvein transfers blood from the placenta to thefetus. Its intrafetal portion ascends by way of thefalciform ligament to join the umbilical segmentof the left portal vein. The umbilical vein and theleft portal vein maintain the same diameter,larger than the right portal vein, which receivesblood primarily recycled through the main por-tal vein. There is therefore a marked preferencein both the quality and quantity of blood flowingthrough the left lobe of the liver, which is notice-ably larger than the right. This situation isreversed in the adult after atrophy of the umbili-cal vein and the ductus venosus.

The left portal vein joins the anterior and pos-terior branches of the right portal vein throughan almost 90 right turn. From this same twist,known as the pars transversa, arises the ductusvenosus, which joins distally with the left hepat-

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Figure 1. A, Posterior view of the paired vitelline veins (VV), umbilical veins (UV),sinus venosus (SV), truncus arteriosus (TA), and bulbus cordis (BC). B, Posteriorview of the changes formed with the goal of introducing right-sided asymmetry in

the adult. C, Posterior view of the mature venous system. indicates atrophied ves-sels. Modified with permission from the McGill Molson Medical Informatics Project

(http://sprojects.mmi.mcgill.ca/embryology/cvs/default.html). IVC indicates inferior

vena cava; PA, pulmonary artery; and SVC, superior vena cava.


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ic vein and the inferior vena cava just proximalto the entrance into the right atrium (Fig. 2).14

The existence of a sphincter that regulatesblood flow through the ductus venosus to theheart remains a subject of debate,2527 as doesthe question of oxygen concentrationdepen-dent anatomic nervous control of the activity ofthis sphincter. Table 1 summarizes the correla-tion of embryonic structures in the venous andarterial systems with the equivalent adultanatomy.

Physiologic CharacteristicsPrincipal vessels such as the ductus venosus,hepatic veins, and inferior vena cava facilitate thetransfer of blood with the highest possible oxy-gen concentration to the fetal heart. However,

the pathophysiologic mechanisms controllingthe function of the human fetal venous circula-tory system are only partially elucidated.

Low placental resistance and improved cardiaccontraction aid in the creation of a pressure gra-dient between the atria and ventricles thatreduces the preload in the venous circulatory sys-tem and allows blood to flow toward the heart.This intimate link between the function of thevenous vascular system and the other elements ofthe fetal circulation is shown physiologically dur-ing fetal breathing movements, which have adirect effect on venous return to the heart.Examination of the effect of fetal breathing move-ments on the circulation in the venous systemrevealed that changes in the pressure gradientbetween the intraabdominal and intrathoraciccavities during breathing movements causedsubsequent changes in blood flow in the venoussystem. Specifically, during inspiration the pres-

sure gradient rose from approximately 0 to 3 toapproximately 22 mm Hg, causing an increase inthe pressure gradient between the umbilical veinand the thoracic part of the ductus venosus andleading to a rise in flow velocity in the umbilicalvein, whereas during expiration the oppositeevents occur.28,29 Other studies showed thatchanges in intrathoracic pressure caused by fetalbreathing movements affect both venous returnto the heart and the arterial system.30

Changes in venous return to the fetal heart canalso influence emptying of the placental bed, as

well as systolic and diastolic blood flow in thearteries. A decrease in venous return causes a dropin placental bed drainage and filling of the heartventricles, resulting in a drop in the end-diastolicvolume of the arteries on the one hand and corre-sponding decline (through the Frank-Starlingmechanism) in stroke volume of the heart on theother side of the system. As a result, these changesmay cause an additional negative effect on venousreturn and flow in the umbilical vein.

Developmental Abnormalities of theHuman Fetal Venous System

We speculate that the normal development ofthe fetal venous system may be disturbed byeither of 2 different events: (1) primary failure totransform or to form the critical anastomosis and(2) secondary occlusion of an already trans-formed system. Thus, on the basis of the type ofvein involved, embryologic precursor, and etio-logic correlation (primary or secondary), we haveclassified them into 4 major groups. Table 2 sum-marizes this classification system.16

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Figure 2. Schematic representation of the fetal umbilical, portal, and hepaticvenous circulations. The arrows indicate the direction of blood flow, and the color

indicates the degree of oxygen content (red, high; purple, medium; and blue, low).

DV indicates ductus venosus; EPV, extrahepatic portal vein; FO, foramen ovale; GB,

gallbladder; HV, hepatic veins; IVC, inferior vena cava; LPV, left portal vein; PS, por-

tal sinus; RA, right atrium; RPV, right portal vein; and UV, umbilical vein. Reprinted

by permission from Ultrasound in Obstetrics and Gynecology.14


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Abnormal Connection of the Cardinal VeinsHeterotaxy syndromes represent a pure exampleof abnormal primary development of thevenous system, with a mouse model existingthat explains the transmission of situs abnor-malities in polysplenia-asplenia syndromes.31,32

Most of these syndromes are associated withcomplex anomalies, especially cardiac malfor-mations that influence the prognosis apprecia-bly; however, cases without notable cardiac

involvement in which fetuses may survive havebeen reported.33 It is in these cases that accu-rate prenatal diagnosis is essential to provideappropriate counseling to the parents. Apartfrom the complex heterotaxy syndromes, iso-lated anomalies of the cardinal veins have alsobeen reported.Absence of the inferior vena cava with azygos

continuation results from primary failure of theright subcardinal vein to connect with the hep-atic segment of the inferior vena cava. Instead, itshunts its blood directly into the right supracar-dinal vein. Hence, the bloodstream that formsthe caudal part of the body reaches the heart byway of the azygos vein and superior vena cava.The persistent left superior vena cava is anotherexample of primary failure to create anastomo-sis and to form the left brachiocephalic vein.

Abnormalities of the Umbilical VeinsAbnormalities of the portal and umbilical veinsform the major group of fetal venous anomalies.These mainly result from primary failure to formthe critical anastomosis, with an aberrant vessel

shunted between the placenta and the systemicveins.13,21,22,34 Several of these cases with anabnormal umbilical vein connection werereported to be associated with Noonan syn-drome. Hydrops fetalis was a common finding inthese fetuses, although the severity of the edemawas out of proportion to the vascular anomaly.This raised the possibility that the finding waslargely attributable to some other cause, per-haps a congenital generalized lymphangiectasia

as manifested in Noonan syndrome.White et al35 offered probably the most con-

vincing explanation of an embryologic basis forthis rare anomaly, introducing the term criticalanastomosis. According to this theory, throughunidentified causes of embryologic maldevel-opment, anastomosis between the umbilicaland vitelline veins fails, and degeneration ofboth umbilical veins occurs in early embryoniclife. As a result, venous blood flow from the pla-centa is blocked, which leads to the opening ofvascular channels through anastomosis to thesupracardinal components of the inferior venacava. Another study showed that in a 7-mm pigembryo there was a connection between theprimitive pelvic venous plexus that drains thelower limb bud and the embryonic umbilicalvein.36

Summarizing the results of these studies, itmay be concluded that in a case of primary fail-ure to form these critical anastomoses, the pla-centa venous return is rerouted to the systemicveins. Primary failure to form the critical anasto-mosis may involve the iliac vein, the superior

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Table 1. Fetal Venous Structures and Their Adult Equivalent Vessels

Embryologic Structure Adult Equivalent

Left anterior cardinal vein Disappears proximally; distal portion contributes to left superiorintercostal vein; anastomoses with right anterior cardinal vein distally

to form left brachiocephalic veinLeft common cardinal vein Oblique vein of left atriumLeft posterior cardinal vein DisappearsLeft horn of sinus venosus Coronary sinusRight anterior cardinal vein Superior vena cavaRight common cardinal vein Superior vena cavaRight posterior cardinal vein Azygos veinDuctus venosus Ligamentum venosumLeft umbilical vein Ligamentum teres distally; degenerates proximally; portion within septum

transversum contributes to hepatic portal systemRight umbilical vein Degenerates proximally and distally; portion within septum transversum contributes

to hepatic portal systemLeft vitelline vein Fuses with right vitelline vein to form portal vein

Modified with permission from the McGill Molson Medical Informatics Project (http://sprojects.mmi.mcgill.ca/embryology/cvs/default.html).


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vena cava, or a direct communication with theright atrium or the left horn of the sinus venosus(coronary sinus; Fig. 3). Noteworthy is a commonfeature of all the aforementioned cases: agenesisof the ductus venosus, a fundamental embryo-logic maldevelopment. Diagnosis of this entity isfeasible today with the widespread use of prena-tal ultrasonography. Although agenesis of theductus venosus was first described more than100 years ago, several cases of neonates with thisanomaly have since been reported.37,38

According to the findings, 2 subgroups may bedistinguished. The first includes fetuses in whichthe umbilical flow entirely bypasses the liver,connecting to the systemic venous circulation asdescribed above, and the second includes fetus-es in whom the umbilical vein drains into theportal vein, thus causing all the umbilical bloodto pass through the hepatic sinusoids. In the for-mer group, many reported cases had an abnor-mal connection of the umbilical vein to the iliacvein, or to the inferior vena cava in its infra-cardiac segment, and some were associated withpleural effusion, hydrops, and Noonan syn-drome.21,22,34 In the latter, an adequate connec-tion between the umbilical vein and the vitellinevenous system was established. The umbilicalvein drains properly into the portal vein but failsto establish a communication with the persistentproximal part of the right vitelline vein. In suchcases, prolonged hyperperfusion of fetal liversinusoids may induce prenatal portal hyperten-sion.22,39

Although complete primary failure to form thecritical anastomoses in both the left and right

umbilical veins is very rare, partial failure to formthe critical anastomosis may be more common.In these cases, in which partial anastomosisbetween the hepatic sinusoids and umbilicalvein fails to develop, blood is then divertedthrough other channels. Two main paths havebeen described, the most common of which isthe persistent right umbilical vein anomaly(Fig. 4).10,16,40 This anomaly is characterized byfailure of the right umbilical vein to form anasto-mosis with the right vitelline vein and degenera-

tion of the left umbilical vein,9,41,42

whereas thesecond, much less common path involves thedirect entry of the umbilical vein into the rightatrium.15,16,43,44

Several pathophysiologic explanations forthese aberrations have been proposed. Jeanty9

suggested that streaming of early flow throughthe right umbilical vein, primary or secondary toocclusion by thromboembolic events arisingfrom the placenta, might cause this anomaly. Inaddition, in experiments involving rats, terato-genic agents such as retinoic acid and folate defi-ciency were found to induce primary failure toform anastomosis and consequently the rightumbilical vein to remain patent.45 Echogenic focifound within the fetal liver suggest a thrombo-embolism occluding the ductus venosus or otherveins, possibly a secondary formation of such ananomaly. In such cases of portal-ductal occlu-sion, oxygenated blood coming from the placen-ta is diverted into the already closed proximal leftumbilical vein, causing reopening of this part ofthe umbilical vein and resulting in a persistentproximal left umbilical vein.46

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Table 2. Proposed Classification System for Abnormal Connections of the Fetal Venous System With the Heart

A. Cardinal veina. Complex malformations, heterotaxic syndromeb. Isolated malformation

B. Umbilical veins

a. Primary failure to create critical anastomosesi. Complete: abnormal connection of umbilical vein (venous shunt) into iliac vein, inferior vena cava, superior vena

cava, and right atriumii. Partial: persistent right umbilical vein with or without ductus venosus

b. Secondary occlusionC. Vitelline veinsa. Primary failure to create critical anastomoses

i. Complete agenesis of portal systemii. Partial agenesis of right or left portal branch (portosystemic shunt)

D. Anomalous pulmonary venous connectiona. Totalb. Partial

Reprinted (order modified) by permission from Ultrasound in Obstetrics and Gynecology.16


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Anomalies of the Vitelline VeinsAbnormalities of the vitelline veins are extreme-ly rare, and only a few have been reported duringfetal life.13,16 Primary failure to form the criticalanastomosis may lead to complete agenesis of

the portal system or partial agenesis of the rightor left portal branch.

Complete absence of the portal system pre-sents an extreme example of total failure of thevitelline veins to transform into the portal sys-tem, stemming from a primary failure to formcritical anastomosis with hepatic sinusoids orumbilical veins. As a result, the enterohepaticcirculation is disturbed, and the portal venousblood is shunted systemically. Mesenteric andsplenic venous blood may drain into the renalveins, hepatic veins, or directly into the inferiorvena cava.4749 To our knowledge, ultrasono-graphic prenatal diagnosis of congenitalabsence of the portal system is rare and has onlybeen described in a single case in which the inutero ultrasonographic appearance of total age-

nesis of the portal system included an intrahep-atic aberrant vessel, absence of the portalsystem, and marked dilatation of the inferiorvena cava.50

Incomplete absence of the portal system orpartial failure to form critical anastomosis mayrepresent a more benign form of vitelline veinabnormalities. Partial primary failure to formcritical anastomosis may result in agenesis of theright portal system, with a persistent left vitellinevein connected directly to the hepatic vein (por-tohepatic shunt) and an absence of the ductus

venosus, with neonatal spontaneous resolution

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Figure 3. Images from a patient referred at 22 gestationalweeks for investigation of cardiomegaly. Fetal echocardiogra-

phy revealed cardiomegaly with dextrocardia and anomalous

venous return to the coronary sinus with agenesis of the ductus

venosus. The diagnosis was confirmed postnatally. A, The solidarrow indicates an aberrant vessel; and dotted arrow, coronary

sinus. B, The arrow indicates the right portal vein; and asterisk,stomach. C, The arrow indicates the dilated umbilical vein.

A

B

C

Figure 4. Persistent right umbilical vein anomaly. AO indicates aorta; GB, gall-bladder; IVC, inferior vena cava; and UV, umbilical vein.


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occurring later in some of these cases.16,51 Inaddition, to our knowledge, only 1 case withagenesis of the right and left portal veins asso-ciated with a portosystemic shunt has been

reported prenatally.

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Anomalous Pulmonary Venous ConnectionAnomalous pulmonary venous connectionmay be separated into 2 subgroups: partial andtotal.

Partial anomalous pulmonary venous con-nection (PAPVC) involves 1 or more, but not all,of the pulmonary veins connecting to the rightatrium or a tributary (Fig. 5). Usually these mal-formations are also accompanied by an atrialseptal defect. Several variant manifestations ofthis anomaly have been reported and includeabnormal insertions of the right pulmonaryveins into the superior or inferior vena cavaand the right atrium and entry of the left pul-monary veins into the left innominate vein.

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Figure 5. Common forms of PAPVC. A, Anomalous connection of the right pulmonary veins (R.P.V.) to the superior vena cava (S.V.C.).A high or sinus venous defect is usual in this anomaly. B, Anomalous connections of the right pulmonary veins to the inferior vena cava(I.V.C.). The right lung commonly drains by 1 pulmonary vein without its usual anatomic 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 leftinnominate vein (L.Inn.V.) by way of a vertical vein (V.V.). An additional left-to-right shunt may occur through the atrial septal defect.

D, Anomalous connection of the left pulmonary veins to the coronary sinus (C.S.). L.A. indicates left atrium; L.V., left ventricle; R.A.,right atrium; and R.V. right ventricle. Reprinted by permission from Heart Disease in Infants, Children, and Adolescents.1


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Visualization of pulmonary veins connecting tothe right-sided cardiac structure involved, whichmay be the superior vena cava, left innominatevein, or coronary sinus, is the basis of echocar-diographic diagnosis of PAPVC. Also, a finding ofright ventricular volume overload with an intactatrial septum may mean that a PAPVC anomalyis present. Doppler flow studies and color map-ping are indispensable in identification andclassification of this group of anomalies.

In total anomalous pulmonary venous con-nection (TAPVC) there is no connection be-tween the pulmonary veins and the left atrium;thus the pulmonary veins drain into the rightatrium or the systemic veins (Fig. 6). About onethird of patients have an associated majoranomaly such as cor biloculare, single ventri-

cle, truncus arteriosus, transposition of thegreat arteries, pulmonary atresia, coarctation,hypoplastic left ventricle, and anomalies of thesystemic veins, whereas the remaining twothirds have isolated TAPVC. Although TAPVC isa rare lesion in its isolated form, occurring inonly about 1 per 17,000 live births, it is one ofthe few emergencies left in pediatric cardiolog-ic practice. This is because neonates withobstructed pulmonary venous return can havesevere decompensation soon after birth, andunlike other forms of congenital heart disease,

maintaining ductal patency by using prosta-glandins is of little help. On the other hand, thesubset of patients with an anomalous connec-tion to the coronary sinus does not tend to haveurgent symptoms, because the drainage to thissite is rarely obstructed.52

Several classification systems for TAPVC havebeen proposed, depending on the level of theanomalous connection. In one system, TAPVC isclassified into 4 types, whether the anomalousconnection is at the supracardiac level (I), car-diac level (II), infracardiac level (III), or 2 or moreof the above levels (IV). An alternate classifica-tion system divides this anomaly into 2 groups:supradiaphragmatic without pulmonary venousobstruction and infradiaphragmatic with pul-monary venous obstruction. An atrial septaldefect or patent foramen ovale is generally pres-ent. The presence of an obstructive lesion in thepulmonary venous channel influences thehemodynamic state and clinical manifestationof TAPVC. This obstruction may occur at theinteratrial septum or may be intrinsic or extrin-sic to the anomalous venous channel.

The aim of echocardiographic evaluation of sus-pected TAPVC lies in locating the site of the con-nection of the common pulmonary vein,evaluating any obstruction of the pulmonary veinsor vertical vein, and confirming or excluding asso-ciated cardiac lesions.53 All forms of TAPVC willhave right ventricle volume overload, an enlargedright atrium, and a bowing leftward of the interatri-al septum. Total anomalous pulmonary venousconnection should be suspected when no pul-monary veins can be visualized entering the leftatrium on the short-axis scan. In addition, thecommon pulmonary channel may be identifiedposterior to the left atrium, with the pulmonaryveins draining into it. The channel may be followedto the site of its connection. In supracardiac formsof TAPVC, the channel will usually drain into an

ascending vertical vein, which in turn may be fol-lowed to a dilated systemic venous structure, mostcommonly the left innominate vein or superiorvena cava. Doppler studies reveal flow in this verti-cal vessel to be cephalad, as opposed to the caudalflow found in the superior vena cava.

In infradiaphragmatic forms of TAPVC, the con-nection is usually at the portal venous system butmay also be to the hepatic veins. The pulmonaryveins converge into a common channel, small andinferior to the left atrium above the diaphragm, orit may appear as a discrete chamber. If untreated,

affected neonates will survive only a few days toapproximately 4 months.

Doppler examination is invaluable in the diagno-sis of all forms of TAPVC. The abnormal color flowsignal may be followed to identify the anomalousconnection as well as the direction and meanvelocity of flow. Turbulence from any obstructionwill produce a mosaic color jet that reveals its loca-tion, whereas pulsed or continuous wave Dopplerimaging allows for quantification of the degree ofobstruction.

The prognosis in cases of PAPVC and TAPVCdepends on the presence and size of the interatrialconnection, the presence of any obstructive lesionin the anomalous venous pathways, the overallstate of the pulmonary vascular bed, and the pres-ence of any cardiac or extracardiac malformations.In cases of TAPVC with obstruction in the anoma-lous venous channel, the neonate usually dies inthe first weeks of life.

The most common anomalies of the fetal sys-temic venous system diagnosed prenatally thathave been described recently are summarized inTable 3.5459

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Figure 6. Common forms of TAPVC. A, TAPVC to the left innominate vein (L.Inn.V.) by way of a vertical vein (V.V.). B, TAPVC to thecoronary sinus (C.S.). The pulmonary veins join to form a confluence designated the common pulmonary vein (C.P.V.), which connects

to the coronary sinus. C, TAPVC to the right atrium. The left and right pulmonary veins (L.P.V. and R.P.V.) usually enter the right atri-um separately. D, TAPVC to the portal vein (P.V.). The pulmonary veins form a confluence from which an anomalous channel arises.This connects to the portal vein, which communicates with the inferior vena cava (I.V.C.) by way of the ductus venosus (D.V.) or the

hepatic sinusoids. L.A. indicates left atrium; L.H., left hepatic vein; L.P., left portal vein; L.V., left ventricle; R.A., right atrium; R.H., right

hepatic vein; R.P., right portal vein; R.V., right ventricle; S.M.V., superior mesenteric vein; S.V., splenic vein; and S.V.C., superior vena

cava. Reprinted by permission from Heart Disease in Infants, Children, and Adolescents.1


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Table 3. Common Anomalies of the Venous System

Anomaly No. of Cases Sonographic Findings/Associated Abnormalities Outcome

Cardinal veinsRight and left isomerism

Atkinson and Drant54

13 7, abnormalities of viscerocardiac status 3, TOP8, RI 7, complete atrioventricular septal defect 10, delivered with all

associated abnormalities5, LI 5, interrupted inferior vena cava;

4, dysrhythmiasHeterotaxy syndromesMarton et al55 13 Congenital heart disease NA

9, SA 10, AV canal4, SIT 10, great vessel anomaly

Cesko et al56 2 None NA1, SI Transposition of the great vessels

1, PSS Cardiovascular malformationOztunc et al57 1, SIT Transposition of the great vessels NA

Umbilical veinsAgenesis of ductus venosus

Hofstaetter et al13 5 2, cardiomegaly; 3, hydrops; 1, 45,X 4, A&W; 1, IUFDAchiron et al16 4 3, cardiomegaly; 1, hydrops 1, neonatal death; 1, TOP;

2, aliveContratti et al38 10 2, increased nuchal translucency; 5, cardiomegaly; 2, neonatal death; 5, alive;

2, chromosomal abnormality; 1, hydrops; 1, TOP; 1, IUFD;3, polyhydramnios; 1, oligohydramnios, IUGR 1, lost to follow-up

Persistent right umbilical veinBlazer et al58 69 60, without additional findings; 68, healthy after birth

4, transient nuchal findings;4, minor anomalies; 1, died after surgery1, diaphragmatic hernia;

Shen et al10 8 7, without additional findings; Healthy after birth1, dextrocardia and right-sided descending aorta

Vitelline veinsComplete agenesis of portal system

Laverdiere et al50 1 Unusual C-shaped vessel between the umbilical vein A&Wand dilated inferior vena cava; no portal vein

Venhat-Raman et al59 1 Liver hyperechoic foci; dilated inferior vena cava; A&Wdilated intraabdominal segment of umbilical vein

Partial agenesis of portal systemAchiron et al16 1 Portohepatic shunt; no portal vein; right cardiomegaly; A&W

partial agenesis of portal system1 Umbilical right atrial shunt; liver hyperechoic foci; A&W

no ductus venosus; partial agenesis of the portalsystem

Pulmonary VeinsTAPVCsAchiron et al16 4 2, asplenia syndrome; 2, asymmetry of cardiac 4, neonatal death

chambers: right > leftAllan and Sharland53 4 2, drainage to the coronary sinus; 3, neonatal death;

1, drainage to the right superior vena cava; 1, alive after successful1, drainage to the inferior vena cava; surgical repair4, asymmetry of cardiac chambers: right > left

A&W indicates alive and well; AV, atrioventricular; IUFD, intrauterine fetal death; IUGR, intrauterine growth restriction; LI, left isomerism; NA,not available; PSS, polysplenia syndrome; RI, right isomerism; SI, situs inversus; SIT, situs inversus totalis; and TOP, termination of pregnancy.


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Conclusions

On the basis of limited clinical experience and atour present state of knowledge, it is difficult to

delineate the fetal and neonatal prognosis whenan anomaly of the fetal veins is detected. How-ever, a few conclusions may be drawn from thecurrent published data. Prenatal evaluation offetuses found to have anomalies of the venoussystem should include a careful search for car-diac anomalies and a detailed anatomic surveyof the umbilical, portal, hepatic, and ductal sys-tems to determine aberrant communicationand, if possible, to delineate hints for systemicdiseases or a thromboembolic phenomenon. Incases with agenesis of the ductus venosus, care-ful follow-up is mandatory, because its absence

may induce the appearance of hydrops fetaliswith an unfavorable prognosis.

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