Systemic Venous Anomalies

Systemic venous anomalies — variations in the superior vena cava (SVC), inferior vena cava (IVC), azygos and hemiazygos veins, hepatic veins, coronary sinus, and innominate vein — usually carry little hemodynamic weight on their own. What makes them genuinely important is procedural: identifying them precisely changes how cardiopulmonary bypass is cannulated, how single-ventricle palliation is staged, and whether a catheter intervention is safe to perform at all. A systematic, segment-by-segment description is the only reliable way to capture the real variability this category contains.

Atrial Situs Predicts the Pattern

Understanding why a given anomaly is likely — or unlikely — starts with situs, because the systemic venous pattern follows it closely.

• Lateralized situs (solitus or situs inversus totalis). The coronary sinus is usually present, and systemic venous anomalies are infrequent and fairly predictable. The single most common anomaly by far is a persistent left SVC connecting to the coronary sinus. In situs inversus totalis, the whole pattern is typically a mirror image of normal.
• Heterotaxy (right or left isomerism). Complex systemic venous anomalies are common — occurring in more than half of all heterotaxy cases — and follow the isomerism type specifically:
  • Asplenia-type (right isomerism): the coronary sinus is often absent, with bilateral SVCs draining directly to the roof of the atria.
  • Polysplenia-type (left isomerism): the coronary sinus is usually present, bilateral SVCs can occur with the left SVC draining to it, and this is also where an interrupted IVC with azygos continuation is most often found.
  • Many additional abnormalities can coexist in heterotaxy, including anomalous hepatic venous connections — so finding one anomaly should prompt a deliberate search for others, not a sense that the workup is complete.

Why the Embryology Is Worth Knowing

Nearly every anomaly in this chapter reflects the persistence of an embryonic connection that should have regressed, or the failure of one that should have formed. The systemic veins develop from three embryonic systems — the umbilical, vitelline, and cardinal veins — with paired anterior and posterior cardinal veins converging into common cardinal veins that drain into the right and left horns of the sinus venosus. Rightward lateralization then commits the venous return to the right atrium, and the individual systemic veins take shape from there.

Systemic vein	Embryologic origin
Superior vena cava	Right anterior cardinal vein
Left innominate vein	Persistent connection between the anterior cardinal veins, after the left anterior cardinal vein regresses
Coronary sinus	Left common cardinal vein (left sinus horn)
Inferior vena cava	Right vitelline vein, right hepatocardiac vein, right subcardinal vein, and the caudal segment of the right supracardinal vein
Hepatic veins	Vitelline and omphalomesenteric veins
Azygos vein	Right supracardinal vein
Hemiazygos vein	Left supracardinal vein

Anomaly	What fails or persists
Left SVC (persistent)	Persistence of the left anterior cardinal vein
Connecting (bridging) vein between bilateral SVCs	A connection forms between the anterior cardinal veins
Atretic right SVC	Regression of the right anterior cardinal vein
Left SVC directly to the LA	Persistent left anterior cardinal vein, with absence or extensive unroofing of the coronary sinus
Levoatrial cardinal vein	Persistent connection between the primordial common pulmonary vein and the cardinal veins
Right SVC to the LA, or to both atria	Leftward, superior displacement of the right sinus horn, or unroofed right pulmonary veins near the SVC–RA junction
Interrupted IVC	Failure of connection between the right hepatocardiac and right subcardinal veins, with the right (or left) supracardinal vein becoming an azygos (or hemiazygos) continuation
Bilateral IVCs	Persistence of the caudal left supracardinal vein
Left IVC to the RA	Persistence of the left supracardinal vein, with regression of the right
Retroaortic innominate vein	An alternate connection forms between the anterior cardinal veins

How to Image the Systemic Veins by Echocardiography

The same discipline applies across every segment: use multiple windows, sweep continuously rather than relying on a single static frame, and add color Doppler to confirm flow direction — 2D alone frequently cannot distinguish a genuine anomaly from a normal variant.

The Superior Vena Cava and Coronary Sinus

• Suprasternal frontal (transverse) view. Shows both SVCs and their relationship to the ascending aorta in one plane, and — with low-scale color mapping — will usually show a connecting (bridging) vein between bilateral SVCs if one is present.
• High left parasternal (sagittal) view. The best view for delineating a left SVC and its continuity with the coronary sinus.
• Subxiphoid sagittal color sweeps. Can show flow from both SVCs and the IVC into the heart together.
• A dilated coronary sinus — the most common cause of which is a persistent left SVC — is seen during a posterior/inferior-to-anterior/superior sweep of a subxiphoid frontal or left anterior oblique (LAO) view, from an apical four-chamber view with posterior angulation, and in the posterior left AV groove on parasternal long-axis. Use a view where the coronary sinus roof is perpendicular to the beam — an apical view with posterior angulation, or a high left parasternal view in a near-sagittal orientation — for the clearest assessment.
• When 2D and color can’t settle the diagnosis, agitated saline injected into the left arm is genuinely useful: with a persistent left SVC to the coronary sinus, contrast appears in the dilated coronary sinus before it appears in the right atrium; with a left SVC draining directly to the left atrium, contrast appears in the left atrium first.

The Inferior Vena Cava, Azygos System, and Hepatic Veins

• Subxiphoid sagittal sweep. Traces the IVC’s full length through the liver, from the kidneys to the right atrium, in a normal heart. Confirming this full length matters specifically to avoid mistaking a prominent hepatic vein for the IVC — a genuine pitfall that can cause an interrupted IVC to be missed.
• Subxiphoid transverse (frontal) views with posterior/inferior angulation. In an interrupted IVC, these show the absence of an IVC-to-RA connection and hepatic veins draining directly to the right atrium instead, along with a dilated azygos vein in cross-section adjacent to the descending abdominal aorta.
• Subxiphoid sagittal views. Especially useful for showing a prominent azygos or hemiazygos vein running parallel to the descending aorta, with flow in opposite directions between the two vessels by color mapping — this opposite-direction flow pattern is the direct confirmatory sign of azygos or hemiazygos continuation.
• Hepatic veins are evaluated through the same subxiphoid frontal and sagittal sweeps, and also from suprasternal views — worth doing deliberately, since some or all hepatic veins can drain anomalously (to the coronary sinus, for instance) or connect separately rather than through a single confluence.

The Innominate Vein

• Suprasternal frontal (transverse) view. Shows the normal left innominate vein coursing anterior to the ascending aorta, typically just below the first aortic arch branch.
• Suprasternal sagittal view, for a retroaortic course. A retroaortic innominate vein appears as two circular structures in cross-section below the transverse arch — the superior one is the vein, the inferior one the right pulmonary artery. On 2D alone, the vein can be mistaken for the right pulmonary artery; a suprasternal frontal sweep confirming two genuinely separate vessels, with color and spectral Doppler, is what resolves the ambiguity.

After a Bidirectional Glenn Procedure

Intraoperative epicardial imaging near the SVC is the standard way to confirm the superior cavopulmonary connection is unobstructed. The Glenn pathway should show low-velocity, phasic flow — set the color Doppler Nyquist limit to around 50 cm/s to assess it appropriately, rather than a standard cardiac-flow setting that would be too high to show subtle narrowing. Even a mild mean gradient of 2 to 3 mmHg across this connection can produce clinically important consequences in single-ventricle physiology, so this deserves careful attention before leaving the operating room, not just a qualitative “looks patent” impression.

Anomalies of the Superior Vena Cava

Persistent Left SVC to the Coronary Sinus (Bilateral SVCs)

The most common systemic venous anomaly overall, and present in about 20% of patients with tetralogy of Fallot. It courses anterior to the left pulmonary artery and aortic arch, between the left atrial appendage and left pulmonary veins, then into the coronary sinus via the left AV groove. Rarely, it instead courses behind the left pulmonary artery, through a region sometimes called the “anatomic vise,” where it can be compressed between the artery and the left bronchus.

• Hemodynamically silent when the coronary sinus is intact — systemic venous return still reaches the right atrium regardless of which SVC it travels through.
• Why it matters procedurally: identifying bilateral SVCs before surgery changes the cannulation approach for bypass, and — if a well-developed connecting vein is present — can allow surgical ligation of the left SVC when needed. Without a connecting vein, a bilateral bidirectional superior cavopulmonary anastomosis may be required instead of a single Glenn procedure, or occasional surgical ligation.
• A missed persistent left SVC in single-ventricle physiology results in a persistent right-to-left shunt and reduced oxygen saturation — a genuine consequence of an incomplete preoperative survey, not a minor omission.
• With an interrupted IVC and azygos continuation to one SVC, a Kawashima procedure is required instead of a standard Glenn, and this changes the timing of the next stage of palliation.

Left SVC to the Coronary Sinus With an Atretic Right SVC

Rare: the left SVC persists while the right anterior cardinal vein regresses, so right-sided head and neck drainage crosses via the innominate vein into the left SVC and then the (dilated) coronary sinus. Associated with an increased incidence of arrhythmias — sinus node dysfunction, WPW, third-degree AV block, AV nodal reentrant tachycardia, and atrial fibrillation. Diagnosed by confirming the absence of a right SVC connecting to the right atrium on subxiphoid LAO or sagittal views, alongside the dilated coronary sinus and left SVC by the techniques above.

Left SVC Directly to the Left Atrium

The vessel runs anterior to the left pulmonary artery and connects directly to the left atrium between the left upper pulmonary vein and the left atrial appendage — most commonly seen in heterotaxy (isomerism) with bilateral SVCs draining to both sides of the atrial mass.

• Without a connecting vein and without an interatrial communication, patients present with reduced oxygen saturation and typically no murmur.
• With a connecting vein and a small or absent interatrial communication, the connecting vein can decompress left atrial blood into the right SVC and right atrium instead (since the right atrium runs at lower pressure) — look for retrograde (cephalad) flow along the left SVC on color mapping as the sign of this decompression.
• In a partially unroofed coronary sinus, a connection persists between the left atrium, the left-SVC-to- coronary-sinus pathway, and the coronary sinus ostium in the right atrium — typically producing a left-to-right shunt (a “coronary sinus-type” ASD) through the dilated ostium. A dilated right heart with a dilated coronary sinus ostium of unclear cause should specifically raise suspicion of a partially or completely unroofed coronary sinus.
• A genuine safety point: a persistent left SVC to the left atrium can cause cyanosis after a Glenn or Fontan procedure, and catheter coil occlusion is often a good solution — but if the coronary sinus ostium is atretic, the left SVC may be the only way coronary venous blood can decompress, and occluding it can cause myocardial ischemia, ventricular dysfunction, or sudden cardiac arrest. Detailed imaging, and a test occlusion before permanent closure, are what prevent this.
• Diagnostic technique: the same high left parasternal and suprasternal frontal views as above, but now with antegrade (caudad) flow along the left SVC into the left atrium on color mapping. Agitated saline in the left arm is again valuable — contrast appears directly in the left atrium first.

Levoatrial Cardinal Vein

An embryologic connection between the pulmonary venous plexus and the cardinal venous system that normally regresses. It can persist as a decompressing pathway when there’s obstruction to pulmonary venous egress or left atrial outflow early in gestation — mitral or left AV valve stenosis/atresia (with or without hypoplastic left heart syndrome) and an intact or restrictive atrial septum, or cor triatriatum.

• Seen on the subxiphoid long-axis sweep as an abnormal vessel draining from a pulmonary vein (or the left atrium) superiorly, away from the heart.
• Suprasternal frontal views show cephalad flow within it, toward the left innominate vein or right SVC.
• Unlike a persistent left SVC, a levoatrial cardinal vein usually courses behind the left pulmonary artery — a genuinely useful distinguishing feature given how similarly the two can otherwise appear.
• A real look-alike: an accessory hemiazygos vein draining into the left innominate vein is a normal variant in a structurally normal heart with normal pulmonary venous connections, and needs to be distinguished from a true decompressing levoatrial cardinal vein by the clinical context — a levoatrial cardinal vein implies genuine upstream obstruction, an accessory hemiazygos vein does not.

Other SVC Anomalies

Congenital SVC obstruction is extremely rare in isolation; acquired obstruction from external compression, thrombus, or — in the congenital heart disease population — after SVC cannulation, sinus venosus defect repair (a Warden procedure), or orthotopic heart transplant with bicaval anastomoses is more common. Diagnosis uses subxiphoid, right sternal border, and suprasternal views, with Doppler used to estimate the mean gradient across the obstruction; TEE is sometimes needed when prior surgery has degraded transthoracic windows.

Anomalies of the Inferior Vena Cava and Hepatic Veins

Interrupted IVC With Azygos or Hemiazygos Continuation

Most common in polysplenia-type heterotaxy, but can occur in situs solitus too. The hepatic segment of the IVC fails to connect, and the right (or, with a left SVC and no right SVC, the left) supracardinal vein enlarges to become an azygos (or hemiazygos) continuation instead — draining superiorly to one of the SVCs. Hepatic venous drainage to the atrial floor is typically preserved regardless.

• Why the diagnosis matters procedurally: vascular access for catheterization and venous cannulation can be genuinely difficult with azygos continuation, and polysplenia-type heterotaxy carries an increased risk of complete heart block, which can make pacemaker placement via an azygos route difficult too.
• In single-ventricle physiology, an interrupted IVC delays and alters the staging of palliation: a Kawashima procedure (bilateral bidirectional superior cavopulmonary anastomosis) connects essentially the entire systemic venous system, except the hepatic veins, to the pulmonary arteries, and Fontan completion later requires specific inclusion of the hepatic veins.
• Imaging: confirm the absence of the IVC-to-RA connection and direct hepatic-to-RA drainage on subxiphoid views, and the dilated azygos/hemiazygos vein running parallel to, with flow opposite to, the descending aorta.

Bilateral IVCs (Duplication)

Uncommon (0.2–0.3% of the general population), from persistence of both supracardinal veins. The clinical significance depends entirely on exactly where the two IVCs join — sometimes the left IVC crosses anterior to the descending aorta to join the right IVC at the renal vein level; connection can occur at other levels too, and each has different practical implications for catheter and surgical access.

Left IVC to the Right Atrium (Absent Right IVC)

Rare (0.2–0.5%): regression of the right supracardinal vein with persistence of the left. The hepatic segment (including the hepatic veins) keeps its normal connection to the right atrium; the caudally located left IVC drains via a prominent hemiazygos vein, or crosses anterior to the descending aorta to join the right hepatic IVC.

Right IVC to the Left Atrium

A genuinely rare, reported anomaly with an intact atrial septum. Preoperative recognition matters specifically to avoid inadvertently diverting IVC flow into the left atrium during surgical ASD closure — a real, avoidable surgical error if the anomaly isn’t identified beforehand. Without an interatrial communication, there’s an obligatory right-to-left shunt and reduced oxygen saturation.

Hepatic Vein Anomalies

Anomalous hepatic venous connection directly to the heart occurs in both heterotaxy types, and occasionally in situs solitus or inversus too. Recognizing anomalous hepatic drainage is critical before a Fontan procedure and before liver transplantation. Failing to identify a separately-connecting hepatic vein before Fontan completion can leave it excluded from the Fontan pathway — the vein then decompresses back into the atrial mass, producing a right-to-left shunt and significant, progressive cyanosis after the operation. Some or all hepatic veins can also drain anomalously into the coronary sinus, producing coronary sinus dilation (see below). Evaluate the IVC and hepatic veins together through subxiphoid frontal and sagittal sweeps, and from suprasternal views.

Coronary Sinus Anomalies

The coronary sinus represents the left horn of the sinus venosus, and — although it drains into the right atrium — is functionally associated with the left atrium, since it runs along the posterior left AV groove. It is characteristically absent in asplenia-type heterotaxy, where the left sinus horn is completely incorporated into the left atrium instead.

Dilated Coronary Sinus

A dilated coronary sinus results from abnormally increased flow or pressure, and has more than one possible cause:

• Persistent left SVC to the coronary sinus
• A coronary sinus-type ASD (partial or complete unroofing)
• Partial or total anomalous pulmonary venous drainage to the coronary sinus
• Partial or total anomalous hepatic venous drainage to the coronary sinus

The correct response to a dilated coronary sinus is a systematic evaluation of the individual pulmonary veins, the hepatic veins, and the left innominate vein — not an assumption that a persistent left SVC is present just because the sinus is large. See Pulmonary Venous Anomalies for the pulmonary-venous causes of coronary sinus dilation in more detail.

Coronary Sinus Ostial Atresia or Stenosis

Extremely rare. Coronary venous blood usually decompresses via a persistent left SVC when this is present, or occasionally via a prominent Thebesian vein, a coronary sinus-type ASD, or a connection with the IVC. Where adequate decompression exists, the clinical course is benign; where it doesn’t, outcomes are poor — which is precisely why even a small left SVC matters so much in this specific setting, and why it must never be ligated, coiled, or occluded without first confirming the coronary sinus ostium is patent. Suprasternal frontal views with color mapping can show retrograde flow from the left SVC into the connecting vein in this situation. Distinguish this from the normal drainage of a prominent superior intercostal, internal thoracic, or left accessory hemiazygos vein into the left innominate vein in the setting of an unrelated small coronary sinus — the clinical stakes of this distinction are genuinely high, since ligating a left SVC under the false assumption that the coronary sinus is independently adequate can cause the same catastrophic consequences described above.

Innominate Vein Anomalies

The normal left innominate vein drains the left subclavian and jugular veins across the front of the aortic arch and ascending aorta into the right SVC. True anomalies (duplication, or absence of the left innominate vein) are exceedingly rare on their own — absence of the innominate vein most often simply reflects bilateral SVCs without a connecting vein.

Retroaortic Innominate Vein

The innominate vein instead courses behind the ascending aorta and below the arch, draining into the right SVC below the azygos connection. Seen in about 1% of congenital heart disease, most often with tetralogy of Fallot or truncus arteriosus and a right aortic arch. No hemodynamic significance on its own, but it affects venous cannulation and the technique of a bidirectional superior cavopulmonary anastomosis, so it needs to be identified before either procedure.

• The look-alike problem: on suprasternal sagittal imaging, a retroaortic innominate vein appears as a second circular structure below the arch, directly resembling the right pulmonary artery in cross-section — 2D imaging alone can genuinely confuse the two.
• Resolving it: a suprasternal frontal sweep demonstrating two truly separate vessels coursing behind the ascending aorta, confirmed with color and spectral Doppler, distinguishes the vein from the artery reliably.

Prenatal Diagnosis

A dilated coronary sinus, seen during the same posterior-to-anterior sweeps used postnatally, is often the first prenatal clue to a persistent left SVC; the vessel itself can also be directly identified in the fetal three-vessel tracheal view, as an additional vessel to the left of the main pulmonary artery in cross-section. For an interrupted IVC, identifying a prominent azygos vein adjacent to the descending aorta during sagittal sweeps of the fetal chest and abdomen is frequently the first clue in utero.

Clinical Importance

Systemic venous anomalies are, individually, rarely dangerous — but the discipline of identifying them precisely, segment by segment, is what prevents real procedural harm: the wrong cannulation site, an excluded hepatic vein after Fontan, an inadvertently diverted IVC during ASD closure, or a coronary sinus ligated without a safe decompression route. See Atrial Septal Defect for the coronary sinus-type defect these anomalies frequently accompany, and Pediatric Transthoracic Echocardiography for the segmental approach to situs and connections that this systematic venous survey builds directly on.