Introduction
Anomalies of the Systemic Veins
Anomalies of the Pulmonary Veins
Anomalies of the Coronary Sinus
In the normal heart, the superior and inferior vena cavea, along with the coronary
sinus, have a characteristic arrangement within the right atrium. It is therefore
appropriate to consider abnormalities of each channel separately, recognizing that, in
rare cases, these anomalies may coexist. Anomalies of the systemic veins are not uncommon,
examples of which include a persistent left superior vena cava connected to the coronary
sinus, interrupted inferior vena cava, and absent right superior vena cava. Anomalies of
the systemic veins are associated with atrial isomerism, an understanding of which is
important in sorting out the various lesions involved. These so-called heterotaxic
syndromes are characterized by failure of many "right-left" differentiation,
leading to ambiguity in viscero-atrial situs, along with anomalies of systemic or
pulmonary venous return. In patients with left atrial isomerism, the infrahepatic portion
of the inferior vena cava is frequently absent, and the venous return from the lower part
of the body enters the superior vena cava via the azygos vein. In patients with right
atrial isomerism, the right and left hepatic veins may enter the ipsilateral sides of the
common atrium, remaining separate from the inferior vena caval entrance.
Abnormalities of the pulmonary veins are also common in both left and right
atrial isomerism; direct connection to the superior or inferior vena cava is more frequent
in right atrial isomerism, whereas anomalous pulmonary venous drainage into the same side
of the atrium as the systemic venous drainage is more frequent in left atrial isomerism.
Frequently there is outflow obstruction to pulmonary arterial blood flow at either the
valvar or subvalvar level. Pulmonary atresia is more common with right atrial isomerism,
whereas pulmonary stenosis is more common in left atrial isomerism. Pulmonary artery
anomalies are not rare, particularly when there is pulmonary atresia with the ductus
arteriosus as the only source of pulmonary blood flow. After the ductus closes, a
"coarctation" commonly develops in the pulmonary artery just at the insertion of
the ductus. The branching pattern of the pulmonary arteries generally assumes one of two
forms, depending on whether left or right atrial isomerism is present. In right atrial
isomerism, both right and left pulmonary arteries tend to look like a normal right
pulmonary artery, with the bronchus for the upper lobe being above the first segmental
artery for the right upper lobe (eparterial bronchus). In contrast, in left atrial
isomerism, the bronchi are below the pulmonary artery at the hilum (hyparterial bronchi),
as is the case for a normal left pulmonary artery. In right atrial isomerism, both lungs
tend to be trilobed, whereas in left atrial isomerism both lungs tend to be bilobed.
Finally, asplenia is more commonly present in right atrial isomerism, whereas polysplenia
is more frequently associated with left atrial isomerism. These features have contributed
to the general rule (which has many exceptions) that patients with right atrial isomerism
tend to have bilateral "right-sidedness", whereas those with left atrial
isomerism tend to have bilateral "left-sidedness".
This discussion in limited to anomalies of the great systemic veins, which
include the superior and inferior vena cava, along with the coronary sinus.[727, 400, 399]
A persistent left superior vena cava is the most common form of anomalous venous
drainage involving the superior vena cava and represents persistence of the left horn
of the embryonic sinus venosus, which normally involutes during normal development to
become the coronary sinus. Almost always, a persistent left superior vena cava enters the
right atrium through the orifice of an enlarged coronary sinus. To this extent, therefore,
the lesion is considered to be an anomaly of the coronary sinus. It characteristically
reaches the heart in the angle between the left atrial appendage and the left pulmonary
veins. The left superior vena cava then runs down the back of the left atrium to enter the
left atrioventricular groove and channel draining blood from the head and both arms. This
is the site in the normal heart of the oblique ligament and vein of Marshall.
A persistent left superior vena cava is of no clinical significance since the systemic
venous blood continues to return to the right atrium, but may be troublesome in keeping
blood out of the field during cardiopulmonary bypass. It may be ligated only in the
presence of a communicating vein between the right and left superior vena cavea. In some
circumstances, the left vena cava may be the only channel draining the head and both arms,
and the usual right superior vena cava is absent.
Rarely, a persistent left superior vena cava can be connected to the roof of the left
atrium between the left atrial appendage and pulmonary veins rather than to the coronary
sinus. This anomaly is termed complete unroofing of the coronary sinus. The orifice
of the coronary sinus then persists as an interatrial communication. A levo-atrial
cardinal vein is a rare venous structure that is found in association with the
hypoplastic left heart syndrome. It provides the only route of exit for pulmonary venous
return, and typically runs along the roof of the left atrium, from the anticipated site of
a left superior vena cava, to the left brachiocephalic vein, and the superior vena cava.
Other rare anomalies of the superior vena cava include a right superior vena cava
connected to left atrium, and a right superior vena cava connecting with both the right
and left atria through separate orifices in the presence of an intact atrial septum.
Aneurysmal dilatation of the superior vena cava is recognized as being an acquired lesion
of the heart and is rarely seen in children.
Anomalies of the inferior vena cava are most commonly an integral constituent of atrial
isomerism, and only rarely is found in patients with usual or mirror-image atrial
arrangements. The most common lesion of the inferior vena cava is that of interruption of
the abdominal portion, with continuation through either the azygos or the hemiazygos
veins. Described simply as ‘azygos continuation’, it is important to always
exclude the existence of left atrial isomerism, which is performed through the
identification of the bronchial morphology and determination of the presence of
polysplenia. When there is interruption of the inferior vena cava with azygos
continuation, all the systemic venous return reaches the morphologically right atrium
through a superior vena cava. With azygos continuation, this is the right-sided vein,
whereas with hemiazygos continuation, the inferior caval blood is returned through a
persistent left superior vena cava.
Morphology
The most frequent morphological anomaly of the coronary sinus is persistence of a left
superior vena cava which drains through the orifice of the coronary sinus. Under these
circumstances, the coronary sinus is enlarged, and the lesion is of no clinical
importance. An unroofed coronary sinus, however, can produce windows into the left
atrium and provide right-to-left intraatrial shunting. The extreme form of this lesion is completely
unroofed coronary sinus, in which the interatrial communication is at the mouth of the
sinus. Isolated coronary sinus windows can occur, however, when there is no
persistent left superior vena cava and when the atrial septum is intact. Other rare
reported anomalies of the coronary sinus include connection of hepatic veins to the
coronary sinus, fistulous connections between the coronary sinus and the coronary
arteries, and connection of the coronary sinus to the inferior vena cava.
The unroofed coronary sinus syndrome consists of total absence of the coronary
sinus, as there is absence of the partition between the coronary sinus and the left
atrium. Individual coronary veins drain separately into both the right and left atria. The
unroofed coronary sinus syndrome with persistent left superior vena cava occurs
when part or all of the common wall between the coronary sinus and the left atrium is
absent, and there is a persistent left superior vena cava. The persistent superior vena
cava usually connects to the left upper corner of the left atrium between the attachment
of the left atrial appendage and the left pulmonary veins. There is often an associated
coronary sinus ASD, which may be further complicated by a confluent partial or complete
atrioventricular septal defect. Other associated lesions include a patent foramen ovale,
ostium secundum ASD, tricuspid atresia, tetralogy of Fallot, and atrial isomerism. Of
considerable importance is that the innominate vein is absent in the great majority of
cases, and the right superior vena cava is frequently small or absent. The inferior vena
cava may cross to the left side below the diaphragm and enters the left hemiazygos vein,
which subsequently drains into the left superior vena cava. The hepatic veins usually
enter the inferior aspect of the right atrium, but they too may connect anomalously to the
inferior left atrial wall.
Hemodynamics
Isolated completely unroofed coronary sinus is associated with a small right-to-left
shunt and is usually of no hemodynamic consequence. In the presence of a persistent left
superior vena cava, however, cyanosis may be mild or severe depending on the degree of
right-to-left shunting.
Clinical Findings & Management
Patients with completely unroofed coronary sinus and persistent left superior vena cava
present with cyanosis. Cerebral embolization and cerebral abscess may also complicate the
clinical picture. The diagnosis of unroofed coronary sinus syndrome is usually made by
echocardiography. Cineangiography may be useful in defining a persistent left superior
vena cava and/or inferior vena cava drainage to the left atrium, in addition to defining
commonly associated abnormalities.
Medical management is usually expectant, and operative correction is usually indicated.
Isolated coronary sinus ASD (isolated unroofed coronary sinus without persistent left
superior vena cava) is treated the same as other types of ASD. Unroofed coronary sinus with
persistent left superior vena cava is approached with the goal of separating the
systemic from pulmonary venous drainage[398]. The most direct method is to resect much of
the atrial septum, leaving a rim of limbus to preserve the conduction system, then
separate the three systemic veins from the four pulmonary veins by means of a pericardial
patch. Left superior vena cava ligation can be safely done if there is a patent crossing
vein connecting the right and left superior vena cavea. A final alternative is to
anastomose the left superior vena cava directly to the left pulmonary artery, although the
experience with this method is limited. When unroofed coronary sinus is associated with
other major cardiac anomalies, the associated anomaly usually presents a clear indication
for operation.
Partial and total anomalous pulmonary venous connections are discussed in the section
on venoatrial malconnections. Discussion in this section is
limited to abnormalities in the structure and function of the pulmonary veins themselves.
Atresia of the common pulmonary vein is a severe malformation which is incompatible
with life unless relieved by urgent surgery. In the absence of coexisting anomalous
pathways (which would be comparable, if present, to the levo-atrial cardinal vein) the
pulmonary venous return is through bronchopulmonary venous anastomoses. Cyanosis and
severe cardiac failure occurring immediately after birth harrowed this defect, which can
be delineated from TAPVR only by failure to demonstrate communicating vein at cardiac
catheterization. Post-natal survivorship depends on small veins connecting the confluence
of the pulmonary veins with the systemic veins or atria. Immediate recognition in
emergency operation are necessary for any chance of survivorship. The operative approach
is the same as for TAPVR, in which the confluence of veins is anastomosed to the left
atrium, thereby restoring pulmonary venous to left atrial continuity. There have been
fewer than 25 cases of atresia of the common pulmonary vein reported and fewer than 10
have been operated upon. Only two known survivors are reported.
Stenosis of the pulmonary veins has a very poor prognosis. Individual veins can be
stenosed but more usually the condition affects all veins. The stenoses can be tubular,
usually with extension into the lung, or discrete. Discrete stenoses tend to be formed at
the point of junction of the veins with the left atrium. The morphology of these various
stenoses suggests that only the discrete variant is amenable to surgical correction. In
such stenoses, the only example of this operable type are in infants with the hypoplastic
left heart syndrome. Obstruction of individual pulmonary veins can also complicate cases
with totally anomalous pulmonary venous connection.
Aneurysmal dilatation of pulmonary veins also occurs (pulmonary varix) and usually
affects individual veins, most often the upper right one. It has been seen in a child of 7
years; it can rupture and cause death. |