Pulmonary Venous Anomalies

Pulmonary venous anomalies span an enormous range — from a variant that’s essentially a normal finding to a life-threatening neonatal emergency — and the vast majority can now be diagnosed rapidly by echocardiography. The common thread across the whole spectrum is technique: identify every pulmonary vein, and follow each one by continuous 2D and color Doppler sweeps to its actual connection, rather than assuming a normal pattern from a partial view.

Normal Anatomy and Why the Anomalies Look the Way They Do

Understanding the anomalies starts with the embryology, because nearly every anomaly in this chapter is a variation on the same developmental step. The lungs and their vasculature form from the splanchnic plexus, and early in gestation the primitive lung drains into the systemic circulation via the umbilicovitelline and cardinal venous systems. At around 32 to 33 days of gestation, a common pulmonary vein establishes a connection with the pulmonary venous plexus and becomes incorporated into the posterior left atrium. Once this connection is established, the earlier pulmonary-to-systemic venous connections are no longer needed and typically regress. With normal incorporation, two right and two left pulmonary veins end up connecting directly and separately to the left atrium. Nearly every anomaly covered here reflects either an abnormal degree of incorporation of the common pulmonary vein, or persistence of an embryonic pulmonary-to-systemic connection that should have regressed.

Four Categories, Worth Keeping Conceptually Separate

• Abnormal numbers of pulmonary veins. Irregular incorporation of the common pulmonary vein — a single vein draining one lung, or occasionally a common vein accepting both sides.
• Normal connections with anomalous drainage. The common pulmonary vein incorporates into the left atrium normally, but interatrial anatomy — most often leftward malposition or malattachment of the septum primum — directs the pulmonary venous inflow into the morphologic right atrium instead.
• Stenotic connections. Individual pulmonary veins, anomalously connecting veins, or the common pulmonary vein itself (producing cor triatriatum) can be narrowed.
• Anomalous connections. One or more veins connect to the systemic venous circulation instead of the left atrium — partial (PAPVC) or total (TAPVC).

How to Image the Pulmonary Veins by Echocardiography

Any detailed assessment of pulmonary venous drainage has to include the systemic venous anatomy, both atria, and the atrial septum together — these structures are inseparable on echo, and a finding in one is often the first clue to an abnormality in another.

Views and Their Relative Strengths

• Subxiphoid. The single most useful window in infants and young children, and where the atrial septum lies most nearly perpendicular to the beam. In both long- and short-axis subxiphoid views, the right upper pulmonary vein can be seen entering the left atrium superiorly and just posterior to the right superior vena cava.
• Parasternal, subclavicular, and suprasternal windows. More useful in older patients, where subxiphoid and suprasternal windows may not adequately show the position of the septum primum. A low parasternal short-axis window is often the most helpful view in this age group.
• High right parasternal and subxiphoid windows. Together, these often give better imaging of the right upper pulmonary vein’s connection than the left parasternal view.
• Suprasternal notch — the “crab view.” Particularly helpful in infants: with the right superior vena cava and left atrial appendage as the “claws,” all four pulmonary veins can often be demonstrated as the “legs” of the crab in a single sweep.
• TEE. A helpful adjunct in older patients with poor transthoracic windows, and can image nearly every pulmonary venous anomaly — but a significant limitation is that connections high in the mediastinum or below the diaphragm may not be completely seen from the esophagus.
• Cardiac MRI or CT. Excellent alternatives for delineating both systemic and pulmonary venous anatomy when a complete diagnosis can’t be reached by echo.

Preoperative Assessment: Key Elements

• Identify each pulmonary vein and its connection site by 2D and color Doppler. Do not assume two veins per lung — the number varies, and an additional vein with a separate connection to a systemic vein (the innominate vein, azygos vein, IVC, or SVC) should specifically be excluded.
• Follow each anomalously connecting vein from its origin to its connection, from multiple views, by continuous 2D and color Doppler sweeps — not a single static image.
• Interrogate every pulmonary vein by spectral Doppler and record the mean gradient, and specifically at any site where color Doppler shows flow acceleration and lumen narrowing.
• In TAPVC, measure the diameter of each pulmonary vein and the smallest diameter of the pulmonary venous confluence — individual vein size is an independent risk factor for recurrent obstruction after repair, so this is a genuine surgical planning requirement, not just descriptive anatomy.
• Image the relationship between the pulmonary venous confluence and the left atrium.
• Rule out mixed drainage — confirm no additional pulmonary vein enters a systemic vein separately — and rule out anomalous systemic venous connections.
• Assess the atrial septum: direction of shunt, and any restriction to flow, by color and spectral Doppler.
• Assess RV volume load (tricuspid annulus diameter, diastolic septal flattening, qualitative or 3D RV size) and RV pressure (tricuspid and pulmonary regurgitation jet velocities, systolic septal configuration).
• Measure LA and LV volumes, and exclude associated cardiovascular anomalies.

Postoperative Assessment: Key Elements

Identify each pulmonary vein and its connection site; interrogate each by spectral Doppler and record mean gradients; measure the left-to-right and superior-to-inferior diameters of the anastomosis between the pulmonary venous confluence and the left atrium; reassess the atrial septum and shunt direction; and reassess RV pressure and volume load exactly as before surgery, since recurrent obstruction is a real, ongoing risk.

Imaging Each Anomaly

Abnormal Number of Pulmonary Veins

The subxiphoid window is ideal in infants and young children; parasternal, subclavicular, and suprasternal windows become more useful in older patients. Careful sweeps are needed to establish the true number of veins and exclude an additional vein with a separate systemic connection — the suprasternal “crab view” is particularly efficient for this in infants.

Normal Connections With Anomalous Drainage

• Typical views: subxiphoid, apical, and high parasternal short-axis — all of which can show the pulmonary veins connecting normally to the posterior left atrium, establish the plane of the septum primum, and demonstrate any abnormal attachment. In older patients, a low parasternal short-axis window is often the most helpful, since subxiphoid and suprasternal views may not adequately show the septum primum’s position.
• Color Doppler is essential, not optional, to demonstrate anomalous drainage toward the anatomic right atrium — 2D alone can look deceptively normal.
• In polysplenia syndrome, the septum secundum is often absent, which removes a landmark otherwise used to identify the anatomic left atrium — establishing left atrial identity by other features becomes more important in this setting.
• Distinguish this from “ipsilateral” pulmonary veins, in which the right pulmonary veins truly connect anomalously to the anatomic right of the right horn of the sinus venosus — a genuinely different anatomic entity that can be confused with simple malposition of the septum primum.
• Spectral Doppler can show restriction to flow from an abnormally attached septum primum, though this is rarely clinically significant.

Pulmonary Vein Stenosis

• Best views: high parasternal windows in general; suprasternal and subxiphoid in younger patients. Evaluate all four veins and their orifices individually by 2D — this is genuinely a vein-by-vein exercise, not a single overview.
• The Doppler signature of obstruction: normal pulmonary venous flow is laminar, low-velocity, and phasic, with a brief retrograde A wave during atrial systole. With increasing obstruction, the A wave disappears, velocity rises, and phasicity is lost. This pattern — not a single velocity cutoff — is what confirms stenosis.
• Technical difficulty is the rule, not the exception: pulmonary vein inflow is rarely parallel to the beam from any standard view, so modified or off-axis views are frequently required for an accurate spectral trace.
• Echo’s real limitation: acoustic dropout from lung tissue means only the distal pulmonary veins and their orifices are reliably imaged. Longer-segment stenosis extending back toward the hilum is better assessed by cardiac MRI, CT, or catheter angiography.
• Indirect signs of significant obstruction: on parasternal short-axis, dilation of the right atrium, right ventricle, and pulmonary artery, with systolic septal flattening indicating RV hypertension.

Cor Triatriatum Sinister

• Best seen from apical views as a curvilinear membrane in the mid-left atrium, separating the pulmonary venous portion from the true anatomic left atrium — often thin, and mobile with changes in filling pressure and flow through the cardiac cycle.
• Parasternal short-axis and subxiphoid views show the membrane’s relationship to the left atrial appendage and the position of the septum primum.
• The diagnostic rule that separates it from a malpositioned septum primum: the left atrial appendage is invariably on the distal (low-pressure) side of the cor triatriatum membrane, and the septum primum position is usually normal. A malpositioned septum primum, by contrast, can be confused with cor triatriatum from some views but doesn’t follow this rule.
• The diagnostic rule that separates it from a supramitral ring: a supramitral ring sits directly on the atrial side of the mitral annulus, does not encompass the left atrial appendage, is often more immobile, and can restrict mitral leaflet excursion through direct valvar attachments — none of which is true of cor triatriatum.
• Assess the atrial septum specifically for the nature of any interatrial communication, and trace each pulmonary vein individually, since partial (“subtotal”) cor triatriatum — involving only one side — and anomalous pulmonary venous connection can both occur alongside it.
• Confirming obstruction: best done from the apical view, even in older patients, since the flow jet across the membrane is often directed toward the mitral valve. Color, pulsed-wave, and continuous-wave Doppler give flow direction and the peak and mean gradient across the orifice.

Partial Anomalous Pulmonary Venous Connection (PAPVC)

• The first clue is often not the anomalous vein itself, but the dilated systemic vein it drains into. Look for this dilation deliberately, rather than waiting to trace the vein directly.
• To the innominate vein or SVC: best evaluated from high parasternal views (both short- and long-axis) and the suprasternal notch; in infants and young children, even the subxiphoid window can show it. Distinguish it from normal systemic venous structures (the azygos or superior intercostal vein) using the same clues — absence of a normally connecting vein to the left atrium, dilation of the innominate vein and SVC, and diastolic septal flattening from RV volume overload.
• To the coronary sinus: best imaged from subxiphoid (particularly in infants and children), parasternal, and apical views. The coronary sinus is typically severely dilated — this should prompt a specific evaluation for a persistent left SVC as well, since that’s the other common cause of coronary sinus dilation. See Systemic Venous Anomalies for the full differential of a dilated coronary sinus and how to image the left SVC.
• To the IVC (scimitar syndrome): most easily imaged from the subxiphoid window, where both short- and long-axis imaging of the IVC are naturally best performed. The anomalously connecting vein can often be seen by 2D and color Doppler joining the IVC just proximal to its junction with the right atrium. A “blunted” contour of the rightward border of the left atrium is a characteristic associated clue. Abnormal cardiac position (mesocardia or dextrocardia) and right pulmonary artery hypoplasia are further clues. When scimitar syndrome is suspected, specifically evaluate the descending thoracic and abdominal aorta for aortopulmonary arterial supply to a sequestered lung segment.

Total Anomalous Pulmonary Venous Connection (TAPVC)

The first clues are a large right-to-left shunt across the atrial septum, inability to image any pulmonary vein draining into the left atrium, and a hypoplastic left atrial chamber — with the pulmonary venous confluence appearing as an echo-free space behind the left atrium. The right heart is typically dilated, with the atrial septum bowing into the left atrium and (with RV hypertension) the ventricular septum bowing into the left ventricle; left-sided structures are often mildly hypoplastic, though rarely too hypoplastic to support a two-ventricle circulation in isolated TAPVC.

The type is defined by the site of connection, and each has its own best views:

• Supracardiac (the most common type): the vertical vein is typically left-sided, ascending anterior to the left pulmonary artery and mainstem bronchus to join the innominate vein — with the innominate vein and SVC usually severely dilated. If the vertical vein instead passes between the left pulmonary artery and the bronchus, it is compressed there, producing obstruction. Best imaged from subxiphoid, high parasternal short-axis, and suprasternal notch views. Right-sided supracardiac connections (to the right SVC or azygos vein) occur too, with the same obstruction risk if the vertical vein passes between the right pulmonary artery and the trachea or bronchus.
• Cardiac: connection to a severely dilated coronary sinus, best imaged from subxiphoid (particularly in infants and children), parasternal, and even apical views in larger patients. As with PAPVC to the coronary sinus, a persistent left SVC needs to be specifically excluded as an alternative cause of the dilation.
• Infradiaphragmatic: a descending vertical vein passes through the esophageal hiatus (just anterior to the esophagus) to connect most often with the portal venous system, or less often the ductus venosus, hepatic vein, or IVC. Individual veins joining the confluence are seen from high parasternal and suprasternal notch views; subxiphoid imaging is crucial for demonstrating the vertical vein’s course and connection below the diaphragm. Obstruction typically occurs at the junction with the portal vein, ductus venosus, or hepatic vein, with the same loss-of-phasicity Doppler signature described above. A genuinely important point: connection to the portal vein is obstructed by definition, even without overt imaging findings of narrowing, because pulmonary venous blood must traverse the hepatic sinusoidal circulation to return to the heart — don’t be falsely reassured by the absence of a discrete narrowing on 2D or color.
• Mixed: the least common type, with variable combinations of the above — this is exactly why every individual vein needs to be traced to its own connection rather than assuming all four share one pathway.

The atrial septum is life-sustaining in every type of TAPVC and needs its own deliberate assessment: type and size of the communication, and presence or absence of restriction. Subxiphoid long- and short-axis views are most helpful, since the septal plane is typically en face to the beam here; parasternal short-axis views help too, with color and spectral Doppler used to size the jet and detect restriction.

Pulmonary hypertension is the rule with obstructed TAPVC, and can be severe — assessing the PDA, when present, by color and spectral Doppler is a useful adjunct for gauging its degree, since suprasystemic PA pressure in systole shows up directly in the ductal Doppler profile.

Physiology: Why the Anatomy Determines the Clinical Picture

• PAPVC behaves physiologically like an ASD — increased pulmonary blood flow from recirculation of oxygenated blood. With a single anomalous vein and an intact atrial septum, the anomalous flow is typically only 20–25% of total pulmonary blood flow, and is rarely clinically apparent. With an entire lung’s drainage anomalous, the fraction rises to about 66% (rather than the 50% one might expect), because the right atrium and ventricle are more compliant than the left-sided chambers. In scimitar syndrome specifically, the net shunt tends to be lower (24–32%), because of the associated right lung parenchymal and vascular abnormality. If a large ASD coexists with PAPVC, the left-to-right shunt increases substantially further, since some of the normally connecting lung’s blood also recirculates through the defect.
• TAPVC without obstruction produces complete mixing of systemic and pulmonary venous blood in the right atrium; because pulmonary resistance is far lower than systemic, pulmonary overcirculation is often 3 to 5 times normal, and systemic saturation can be 90% or higher — cyanosis that’s often clinically inapparent. With obstruction, pulmonary venous hypertension develops in the affected segment and, as more of the lung is affected, is transmitted back through the pulmonary vascular bed to produce pulmonary capillary and arterial hypertension, with acute pulmonary edema and reflex vasoconstriction giving way to chronic vascular remodeling — right heart compensatory hypertrophy, then dilation, then contractile dysfunction and failure. The size of the interatrial communication is critical: as it becomes more restrictive, pulmonary overcirculation and pulmonary hypertension both worsen and systemic output falls — a genuinely dangerous combination. Infants with obstructed TAPVC typically present within the first weeks of life with rapidly progressive dyspnea and cardiorespiratory failure.

Prenatal and Adult Imaging

Prenatal Assessment Is Genuinely Difficult

Pulmonary venous return contributes only a small fraction of fetal combined ventricular output (roughly 7%), which makes pulmonary venous anomalies — particularly PAPVC — challenging to diagnose in utero and infrequently detected before birth. Pulmonary veins are best seen from the fetal four-chamber and short-axis views, with color and pulsed-wave Doppler used to confirm normal or abnormal drainage. Indirect clues — right heart dilation, great artery disproportion, or mild LA hypoplasia — should prompt as complete an evaluation as possible, but these signs are nonspecific and also occur with coarctation, other left-sided obstructive lesions, or an arteriovenous malformation, so they don’t confirm the diagnosis on their own. A visible venous confluence behind the left atrium, or a vertical vein, supports TAPVC; findings suggestive of scimitar syndrome include dextrocardia and right pulmonary artery hypoplasia. Malposition of the septum primum with anomalous drainage is especially hard to establish prenatally, since some leftward deviation of the septum primum into the left atrium is a normal fetal finding — heterotaxy features with polysplenia should raise suspicion when present.

Adult Imaging Has Its Own Pattern of Limitations

Technical limitations dominate: subxiphoid and suprasternal windows suffer from increased probe-to-structure distance. The high parasternal short-axis view is often the most useful in larger patients, showing the atrial septum, the lower pulmonary veins, and frequently the left upper pulmonary vein. The right upper pulmonary vein is difficult to image from this position in larger patients — the high right sternal border view helps here, and is also useful for excluding a sinus venosus defect. Indirect evidence — right heart chamber enlargement and diastolic septal flattening on parasternal short-axis — can be seen even in the largest patients when direct imaging fails. TEE is an excellent alternative, giving clear imaging of the atria, atrial septum, pulmonary veins, and venae cavae from multiple planes, and can diagnose nearly every pulmonary venous anomaly — cor triatriatum, sinus venosus defect, and PAPVC among them. Its real limitation is the same one noted above: it can’t completely image connections that are high in the mediastinum or below the diaphragm. Cardiac MRI or CT are excellent alternatives in this setting, with the added benefit of accurately quantifying RV size, function, and the pulmonary-to-systemic flow ratio.

Echocardiographic Guidance of Treatment

Treatment for the majority of pulmonary venous anomalies, where indicated, is surgical; transcatheter techniques (balloon dilation, cutting-balloon dilation, and stenting, including drug-eluting stents) exist for congenital or acquired pulmonary vein stenosis, but the underlying disease tends to be progressive and frequently recurs even after treatment — surveillance imaging genuinely matters here, not just at the index procedure. Surgical results for pulmonary vein stenosis have also historically been disappointing long-term, though the newer “sutureless” technique has improved recurrence rates, particularly combined with transcatheter and medical therapy.

• In the catheterization laboratory, angiography is typically used for intraprocedural guidance, with echo used afterward to follow pulmonary vein status and RV/PA pressure noninvasively.
• Intraoperative TEE is genuinely valuable for repair of sinus venosus defects, other forms of PAPVC, cor triatriatum, and TAPVC — including 3D TEE in older children and young adults. For PAPVC repairs involving complex venous baffling, TEE is excellent for confirming patency of both venous pathways and detecting residual leaks.
• TEE evaluation of TAPVC repair specifically is more challenging: the surgical anastomosis often sits directly anterior to the esophagus, sometimes too close to the probe for complete color and pulsed Doppler interrogation. In small infants, probe-related distortion or compression of the pulmonary venous pathway is a real risk to keep in mind. Epicardial imaging is a good alternative in this situation, avoiding both limitations.

Clinical Importance

The pulmonary venous anomalies share one discipline: trace every vein individually, from origin to connection, by continuous sweeps and color Doppler rather than a single static view — because the number of veins varies, the connection can be anomalous while still “looking normal” until color Doppler is added, and a dilated systemic vein is often the first and only clue before the anomalous vein itself is directly seen. See Atrial Septal Defect for the broader atrial-septal framework that PAPVC and TAPVC both depend on, and Coarctation of the Aorta for another lesion whose indirect echo clues (right heart enlargement, chamber disproportion) can overlap with those described here.