MR Imaging and CT Evaluation of Congenital Pulmonary Vein Abnormalities. Infants 1 PEDIATRIC IMAGING

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1 Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at PEDIATRIC IMAGING MR Imaging and CT Evaluation of Congenital Pulmonary Vein Abnormalities in Neonates and Infants 1 87 ONLINE-ONLY CME See /rg_cme.html LEARNING OBJECTIVES After completing this journal-based CME activity, participants will be able to: Identify common congenital anomalies of the pulmonary veins. Discuss use of MR imaging and CT in diagnosing these anomalies in neonates and infants. Describe the anatomic and physiologic information desired from imaging. Himesh V. Vyas, MD S. Bruce Greenberg, MD Rajesh Krishnamurthy, MD Magnetic resonance (MR) imaging and computed tomography (CT) are increasingly being used in diagnosis and follow-up of congenital pulmonary vein anomalies in neonates and infants. Such anomalies include total or partial anomalous pulmonary venous return, sinus venosus defect, malposition of the septum primum, cor triatriatum, pulmonary vein atresia or stenosis, and abnormal number or course of the pulmonary veins. MR imaging provides a wealth of anatomic and functional data that are valuable in case management and planning intervention. Gadolinium-enhanced MR angiography is the mainstay of anatomic evaluation. Ventricular volumetry with two-dimensional steady-state free-precession sequences and flow analysis with cine phase-contrast imaging provide physiologic information that may be used to calculate the degree of right heart enlargement and the shunt fraction, allowing the cardiologist to determine the functional importance of the lesion. CT provides superior spatial resolution and short imaging times but at the expense of exposure to ionizing radiation. RSNA, 2012 radiographics.rsna.org Abbreviations: CPV = common pulmonary vein, GRE = gradient-echo, IVC = inferior vena cava, PAPVR = partial anomalous pulmonary venous return, Qp = pulmonary blood flow, Qs = systemic blood flow, RUPV = right upper pulmonary vein, SSFP = steady-state free precession, SVC = superior vena cava, TAPVR = total anomalous pulmonary venous return, 3D = three-dimensional RadioGraphics 2012; 32:87 98 Published online /rg Content Codes: 1 From the Department of Pediatrics, Divisions of Cardiology (H.V.V.) and Radiology (S.B.G.), University of Arkansas for Medical Sciences and Arkansas Children s Hospital, 1 Children s Way, Slot 512-3, Little Rock, AR ; and E. B. Singleton Department of Pediatric Radiology, Texas Children s Hospital, Baylor College of Medicine, Houston, Tex (R.K.). Received December 23, 2010; revision requested January 3, 2011; final revision received September 30; accepted October 10. For this journal-based CME activity, the author (H.V.V.), editor, and reviewers have no relevant relationships to disclose. S.B.G. is a speaker for Toshiba and consults for Vital Images. R.K. consults for Eisai and receives research support from Philips. Use of gadolinium chelates for MR angiography in children is considered off-label use. Address correspondence to H.V.V. ( vyashimeshkumar@uams.edu). RSNA, 2012

2 88 January-February 2012 radiographics.rsna.org Table 1 Relative Advantages and Disadvantages of Commonly Used Modalities in Definition of Pulmonary Vein Anomalies Criteria Echocardiography MR Imaging CT Angiography Catheterization Availability Excellent Fair Excellent Fair Duration of study (not Long Long Short Long including anesthesia) Study limited by acoustic Yes No No No windows Exposure to radiation No No Yes Yes Capability for 3D No Yes Yes Usually not reformation Provision of physiologic information (flowvolume analysis) Limited Note. 3D = three-dimensional. Excellent (flow and volume analysis possible) Limited (volume analysis possible but requires increased radiation exposure, no flow analysis) Good (flow analysis and shunt calculation possible, volume analysis not easy) Introduction Abnormalities of the pulmonary veins are frequent in patients with congenital heart disease and are particularly common in patients with abnormalities of atrial and visceral situs such as heterotaxy (1). These abnormalities range across the entire spectrum from incidental findings to conditions that are lethal if untreated. Accurate definition of the nature and extent of these abnormalities is critical to decision making about treatment. Although any of these abnormalities may be suspected at echocardiography, definitive imaging of the pulmonary veins is a limitation of echocardiography owing to lack of acoustic windows. Complementary imaging in the form of cardiac magnetic resonance (MR) imaging or computed tomography (CT) is frequently used as an alternative to invasive cardiac catheterization. Table 1 lists the advantages and disadvantages of these four commonly used modalities in definition of pulmonary vein abnormalities. With its excellent safety profile and ability to provide anatomic and physiologic information, it is easy to see why MR imaging is the method of choice for delineation of pulmonary vein abnormalities (2). One exception is the case of a pulmonary venous obstruction in a newborn infant with inconclusive findings at echocardiography. In this situation, a lengthy MR imaging examination is not desirable, and urgent definition of pulmonary venous anatomy is best achieved by means of ungated CT angiography without use of sedation. In this article, we describe various congenital pulmonary vein anomalies with an emphasis on embryology, morphology, appropriate indications for use of MR imaging and CT in neonates and infants, MR imaging and CT technique, and pertinent imaging manifestations. A typical MR imaging protocol used in evaluation of pulmonary vein anomalies in neonates and infants is given in Table 2. Embryology of the Pulmonary Veins The lung buds develop from the foregut and have systemic arterial supply and venous drainage to the cardinal system (1,3). The common pulmonary vein (CPV) develops from the primitive left atrium and grows toward the lungs, establishing connections with the pulmonary venous system. The primitive connections of the lungs to the cardinal venous system regress over time, with the pulmonary veins draining to the left atrium. As the left atrium expands, it incorporates both of the CPVs and eventually the four connecting pulmonary vessels. As the atrial wall expands, the smooth tissue of the pulmonary veins is incorporated into the atrial wall. The trabeculated tissue of the primitive atrium is displaced anteriorly and laterally, forming the left atrial appendage. Congenital Pulmonary Vein Anomalies Commonly encountered abnormalities of the pulmonary veins are as follows: (a) anomalous pulmonary venous drainage, which includes total

3 RG Volume 32 Number 1 Vyas et al 89 Table 2 Typical MR Imaging Protocol for Evaluation of Pulmonary Vein Anomalies in Neonates and Infants Sequence Parameters Advantages Limitations Black-blood T1W EPI TR = one R-R interval, TE = 20 msec, ETL of 5, three to four signals acquired, FOV and matrix size to keep voxel size <1.5 2 mm, no parallel imaging, free breathing Cine SSFP Retrospective ECG gating, TR = msec, TE = msec, FA = 45, views per segment = 10 20, reconstructed images per cardiac cycle = 20 30, FOV and matrix size adjusted so that spatial resolution is <2 mm; for short-axis stack imaging (volumetry), at least 12 contiguous short-axis slabs perpendicular to long axis of ventricles are obtained during brief periods of breath holding with section thickness = 5 6 mm and intersection gap = 0 2 mm; parallel imaging is generally used; usually one signal is acquired; if patient has difficulty holding breath, sequence may be performed as free-breathing acquisition with two to four signals acquired Segmented k-space cine GRE Cine phasecontrast GRE Gadoliniumenhanced MRA Retrospective ECG gating, TR = 6 7 msec, TE = 2 3 msec, FA = 40 50, segmented k-space, free breathing, three signals acquired, section thickness = 3 mm with 1-mm overlap, parallel imaging Retrospective ECG gating, TR = 8 20 msec, TE = 5 7 msec, FA = 15 30, voxel size = mm, section thickness = 6 10 mm, frames per cycle = 20 30, free breathing with three signals acquired, appropriate velocity encoding* for structure of interest Gadolinium dose = 0.2 mmol/kg, non ECG-gated 3D spoiled fast GRE sequence, TR = 5 9 msec, TE = msec, FA = 30 45, rectangular FOV and matrix size adjusted to produce nearisotropic voxels with spatial resolution of ~ mm; centric k-space filling may be used to reduce acquisition times; temporal undersampling techniques like keyhole imaging can provide dynamic information about pulmonary perfusion Anatomic imaging, less prone to artifacts Cine imaging, high SNR, excellent depiction of intracardiac anatomy Free-breathing acquisition, thinsection imaging, dephasing artifact from stenosis used as diagnostic aid Used for flow and velocity mapping Method of choice for visualizing pulmonary veins Static images, longer imaging time Highly prone to artifacts, thus use limited in neonates and infants due to flow artifacts Longer imaging time than SSFP sequence with lower temporal resolution Turbulent flow makes measurements unreliable, very small vessels are not adequately studied, prone to artifacts, errors if performed obliquely to vessel of interest... Note. ECG = electrocardiographic, EPI = echo-planar imaging, ETL = echo train length, FA = flip angle, FOV = field of view, GRE = gradient-echo, MRA = MR angiography, SNR = signal-to-noise ratio, SSFP = steady-state free precession, TE = echo time, T1W = T1-weighted, TR = repetition time. *Appropriate velocity encoding = cm/sec for normal great vessels and cm/sec for normal veins. anomalous pulmonary venous return (TAPVR), partial anomalous pulmonary venous return (PAPVR), sinus venosus defect, and malposition of the septum primum; (b) pulmonary vein stenosis or atresia, which includes cor triatriatum, congenital pulmonary vein atresia or stenosis, and recurrent pulmonary vein stenosis after repair of anomalous pulmonary venous return; and (c) miscellaneous or

4 90 January-February 2012 radiographics.rsna.org incidental abnormalities, which include abnormal number of pulmonary veins and abnormal course of the pulmonary veins. In the remainder of this article, we discuss some of these pulmonary vein abnormalities individually. Total Anomalous Pulmonary Venous Return Embryologically, TAPVR is thought to result from failure of the CPV to connect to the left atrium, with persistence of the primitive splanchnic connections of the pulmonary veins to the cardinal systemic veins and thence to the right atrium. This defect is usually isolated but may be a component of complex heart disease such as heterotaxy. Four broad categories of TAPVR are recognized according to where the anomalous veins drain: supracardiac, cardiac, infracardiac, and mixed. The supracardiac type is the most common form of TAPVR. The pulmonary veins drain to a confluence (usually oriented horizontally) posterior to the left atrium. An ascending vertical vein originates from this confluence and travels behind the left atrial appendage and, usually, anterior to the left pulmonary artery (Fig 1). However, occasionally this vein may travel posterior to the left pulmonary artery and may become trapped in a vice between the dilated artery and the left bronchus, leading to pulmonary venous obstruction (Fig 2). The vertical vein finally drains into the innominate vein. Occasionally, the site of entrance to the innominate vein may also be narrowed, leading to obstruction. The innominate vein and SVC are dilated. The right heart is usually dilated due to the volume overload. There is always an atrial septal defect or patent foramen ovale, which is the only source of flow to the left heart. In the cardiac type of TAPVR, the pulmonary venous confluence connects directly to the right atrium, usually through the coronary sinus. The pulmonary veins and coronary sinus are significantly dilated, and echocardiography shows a characteristic whale s tail appearance. Obstruction is unusual in this form of TAPVR. Less common forms of intracardiac TAPVR include TAPVR to the right SVC, TAPVR directly to the right atrium, and TAPVR to the azygos vein, which is often obstructed. In the infracardiac type of TAPVR, the pulmonary venous confluence drains to systemic veins below the diaphragm. The confluence is usually posterior to the left atrium and vertically oriented (sometimes described as an inverted fir tree ). Figure 1. Nonobstructive supracardiac TAPVR. CT angiogram shows that all the pulmonary veins return to a confluence, from where an ascending vertical vein (*) arises and drains to the innominate vein (INNV). The innominate vein and superior vena cava (SVC) are dilated. RA = right atrium. From here, a descending vein arises and passes through the esophageal hiatus. Most commonly, this vein connects to the portal vein (at the confluence of the splenic and superior mesenteric veins) (Fig 3). Less often, the connection is to the ductus venosus, hepatic veins, or inferior vena cava (IVC). Patients with infracardiac TAPVR have a high prevalence (>90%) of obstruction. Such patients typically present as neonates with severe respiratory distress. Patients with mixed TAPVR have varying combinations of the three types described earlier. An example includes connection of the right pulmonary veins to the coronary sinus and connection of the left pulmonary veins to the innominate vein (Fig 4). In most neonates with TAPVR, complete anatomic delineation of the defect is possible with echocardiography alone. However, in certain situations patients may need more advanced imaging with MR imaging or CT. These circumstances include the presence of poor echocardiographic acoustic windows; uncertainty about the presence of mixed TAPVR; and cases of TAPVR associated with complex heart disease, such as heterotaxy syndromes, in which complete delineation of arterial and venous anomalies is critical and imaging with echocardiography alone may not be adequate. The MR imaging protocol for TAPVR is primarily focused on evaluation of the status of the pulmonary and systemic vasculatures. An important point is that patients with TAPVR are usually

5 RG Volume 32 Number 1 Vyas et al 91 Figure 2. Obstructive supracardiac TAPVR in a neonate with heterotaxy. (a) Coronal black-blood echoplanar T1-weighted MR image shows bilaterally symmetric morphologic right bronchi (arrows) with early takeoff of the upper lobe branch, a finding consistent with asplenia. (b) Coronal black-blood echo-planar T1-weighted MR image shows severe narrowing (arrow) of a right-sided ascending vertical vein (*) as it passes between the right pulmonary artery and right bronchus (anatomic vice). Figures 3, 4. (3) Infracardiac TAPVR. Volume-rendered MR angiogram (posterior projection) shows all the pulmonary veins returning to a vertically oriented confluence. A descending vein (*) passes through the diaphragm to terminate in the hepatic or portal veins. (4) Mixed TAPVR. (a) Volume-rendered MR angiogram (posterior projection) shows the left lower pulmonary vein and both right pulmonary veins (*) draining into the coronary sinus (CS). (b) Volume-rendered MR angiogram (left anterior oblique projection) shows the left upper pulmonary vein draining via an ascending vertical vein (arrow) to the innominate vein (INNV).

6 92 January-February 2012 radiographics.rsna.org Figure 5. Scimitar syndrome in a pregnant patient. Because of the pregnancy, gadolinium contrast material was not used. Complete anatomic and physiologic diagnosis was achieved with a combination of black-blood and cine SSFP imaging. (a) Axial black-blood T1-weighted MR image shows dextroposition of the heart and a small right pulmonary artery (*) relative to the left pulmonary artery, findings suggestive of scimitar syndrome. (b) Cine SSFP image shows a descending anomalous vein (arrow) draining below the diaphragm. In this patient, the IVC was interrupted and the descending right pulmonary veins drained to the hepatic veins. neonates, who are potentially clinically unstable and require a short and efficient MR imaging study. The MR imaging protocol includes axial cine GRE imaging with 3- to 4-mm section thickness and with overlap to diminish errors related to volume averaging, thin-section black-blood imaging in the axial or coronal plane (or both) through the chest, and high-resolution gadolinium-enhanced 3D MR angiography (4). CT may be particularly advantageous in critically ill neonates with obstructive TAPVR. Nongated CT allows accurate diagnosis with very short imaging times, avoiding the need for sedation, and may be the modality of choice in such critically ill neonates. Partial Anomalous Pulmonary Venous Return Embryologically, PAPVR occurs when some but not all segments of a developing lung fail to establish connections with the CPV and instead retain their connections to the primitive splanchnic system of the cardinal veins. The most common form of PAPVR is drainage of the right pulmonary veins to the SVC, with or without a sinus venosus defect (5). (Sinus venosus defect is discussed in the next section.) Other common forms of PAPVR are drainage of the left pulmonary veins to the innominate vein, drainage of the right or left pulmonary veins to the coronary sinus, and drainage of the right pulmonary veins to the IVC; the latter is termed scimitar syndrome (1,3,6). Scimitar syndrome may be associated with hypoplasia of the right lung. In turn, right lung hypoplasia results in hypoplasia of the right pulmonary artery, dextroposition of the heart, pseudosequestration of the affected right lower lobe, and development of aortopulmonary collateral arteries. The aortopulmonary collateral arteries may occasionally be large enough to cause pulmonary arterial hypertension (Fig 5). Except for patients with scimitar syndrome, most patients with PAPVR are relatively older at presentation and do not have cyanosis. The primary physiologic process is a large left-to-right shunt, similar to that in cases of atrial septal defect. Patients with PAPVR present with heart murmurs, fatigue, dyspnea, and arrhythmias. Many patients are asymptomatic, particularly in childhood. Uses of MR imaging include gadolinium-enhanced MR angiography for precise anatomic delineation of the number and drainage of involved veins with a resolution not achieved with echocardiography. Furthermore, MR imaging allows quantification of the left-to-right shunt and right heart size with flow analysis and volumetry. These functional data can be important in decision making in borderline cases, since the indications for intervention include the presence of right heart dilatation (from volume overload) in the presence of a hemodynamically significant shunt (ratio of pulmonary blood flow [Qp] to systemic blood flow [Qs] 1.5:1).

7 RG Volume 32 Number 1 Vyas et al 93 Figure 6. Sinus venosus defect. (a) Volume-rendered MR angiogram (right anterior oblique projection) shows PAPVR of the right upper and middle pulmonary veins to the SVC (arrow). (b) Volume-rendered MR angiogram (left posterior oblique projection) shows communication of the left atrium with the SVC and right atrium through the defect (arrow). (c) Axial bright-blood MR image shows entrance of the RUPV into the SVC (arrow). AA = ascending aorta, DA = descending aorta, RPA = right pulmonary artery. (d) Axial bright-blood MR image obtained caudal to c shows the defect (*), which is actually the dilated ostium of the normally connected RUPV. LA = left atrium, RA = right atrium. Previously, the standard of reference for making these measurements was invasive cardiac catheterization; however, MR imaging has been validated as an accurate method for noninvasive quantification of intracardiac shunting (7). Right ventricular volumes derived with MR imaging have also been shown to have excellent reproducibility, and MR imaging is now considered the standard of reference for assessment of right ventricular size (8). In patients with scimitar syndrome, demonstration of aortopulmonary collateral vessels with MR angiography is essential (9). The imaging protocol includes cine twodimensional SSFP or segmented k-space cine GRE image stacks in the axial plane to track the course of the extracardiac vasculature, followed by gadolinium-enhanced 3D MR angiography (10). Ventricular volumes are assessed with a cine SSFP image stack in the short-axis plane. The amount of left-to-right shunting is quantified with cine phase-contrast flow analysis of the aorta and main pulmonary artery to estimate the Qp/Qs ratio. CT does not offer any specific advantages in evaluation of this anomaly and does not provide some of the physiologic information provided by MR imaging. In addition, CT involves exposure to ionizing radiation. Sinus Venosus Defect Embryologically, sinus venosus defect is considered to represent unroofing of the right pulmonary veins into the SVC or IVC (11). Thus, unroofing of the right upper pulmonary vein (RUPV) into the SVC is called sinus venosus defect of the SVC type, while unroofing of the right lower pulmonary vein into the IVC is called sinus venosus defect of the IVC type. Involvement of the right middle pulmonary vein is variable and can occur with either type of sinus venosus defect. The term sinus venosus atrial septal defect is a misnomer, since the true atrial septum is not involved in these defects. Sinus venosus defect is a defect in the wall that separates the SVC right atrial junction from the posterior and superior aspect of the left atrium and is extraseptal in location. In addition, owing to unroofing of the RUPV into the SVC, the RUPV drains anomalously into the SVC, while the SVC overrides the sinus venosus defect and is committed to both atria (Fig 6).

8 94 January-February 2012 radiographics.rsna.org Figure 7. Malposition of the septum primum. LA = left atrium, RA = right atrium, arrow = expected normal position of the atrial septum. (a) Bright-blood MR image of the atria shows leftward curvature of the atrial septum posteriorly, causing the normally connected RUPV (*) to drain anomalously into the right atrium. (b) Bright-blood MR image obtained caudal to a shows the same findings and anomalous drainage of the normally connected right lower pulmonary vein (*) to the right atrium. LV = left ventricle, RV = right ventricle. Functionally, the behavior of sinus venosus defect is like that of a large atrial septal defect, producing a left-to-right shunt (RUPV to SVC). Patients with sinus venosus defect present with symptoms of right ventricular volume overload, including fatigue, dyspnea, and arrhythmias. Younger individuals are often asymptomatic and may present with a heart murmur. Indications for MR imaging include an unclear diagnosis or incomplete definition of involved pulmonary veins at echocardiography. In most cases, acquisition of functional information such as shunting and volumes typically is not clinically necessary, since the defect is almost always large and unrestrictive and the diagnosis alone is an indication for intervention. The imaging protocol includes axial cine SSFP imaging (12), 3D SSFP imaging (13,14), or both. Anomalous right pulmonary veins, which are a constant feature of this diagnosis, are best demonstrated with gadolinium-enhanced 3D MR angiography. Volumetric analysis of the degree of right heart dilatation and estimation of the Qp/Qs ratio complete the MR imaging protocol. As in patients with PAPVR, CT does not offer any specific advantages in patients with sinus venosus defect and does not provide some of the physiologic information provided by MR imaging. Hence, MR imaging is the technique of choice when advanced imaging is required in patients with sinus venosus defect. Malposition of the Septum Primum The septum primum develops as a thin partition in the primitive atrium, dividing it into the right and left atria. This structure ultimately forms the thin flap valve of the fossa ovalis, while the stiffer septum secundum grows from the roof of the right atrium to the right of the septum primum. The septum secundum ultimately forms the thicker limbus of the fossa ovalis. The right pulmonary veins drain just to the left of the cephalic attachment of the septum primum. Rarely, the septum primum may be deviated leftward such that the normally connected right pulmonary veins drain anomalously to the right atrium (Fig 7) (15). With extreme degrees of malposition, even the left pulmonary veins may drain anomalously. Thus, malposition of the septum primum results in anomalous drainage of normally connected right pulmonary veins (15,16). With extreme degrees of malposition, left heart hypoplasia may also result due to lack of left heart filling. Malposition of the septum primum is typically associated with heterotaxy and polysplenia. The clinical picture is dominated by the presence of associated complex cardiac anomalies, which are frequent in patients with heterotaxy. This defect is typically diagnosed with highquality echocardiography; MR imaging and CT are usually not necessary to make the diagnosis. However, malposition of the septum primum may be encountered during imaging of complex cardiac defects and must be distinguished from

9 RG Volume 32 Number 1 Vyas et al 95 Figure 8. Cor triatriatum. (a) Frontal plain radiograph shows evidence of pulmonary venous congestion. (b) Maximum intensity projection MR angiogram shows the cor triatriatum membrane (arrow) in the left atrium (LA). LV = left ventricle, RA = right atrium, RV = right ventricle. other forms of PAPVR or TAPVR because the treatment is different, involving resection and repositioning of the atrial septum in a more normal position. Furthermore, when this anomaly occurs in the setting of heterotaxy syndromes, complex congenital heart defects are frequently associated and accurate definition of venous and arterial anomalies is necessary. The MR imaging protocol consists of axial and four-chamber cine SSFP or cine GRE imaging, which shows the anomaly well. Gadolinium-enhanced MR angiography is important to demonstrate other associated venous and great arterial abnormalities that frequently coexist. In clinically stable patients who can tolerate the longer imaging time of MR imaging, this technique is preferable when echocardiography alone is not sufficient. CT may be preferable in acutely ill patients with heterotaxy syndromes, in whom the short imaging duration is advantageous. However, visualization of intracardiac anatomy requires cardiac gating and therefore carries a significantly higher radiation exposure. Cor Triatriatum Embryologically, cor triatriatum is thought to result from defective resorption of the CPV into the left atrium, with associated stenosis of the CPV orifice. As a result, primitive splanchnic connections may persist, depending on the stage of development during which the abnormality occurs. These primitive splanchnic connections provide alternative routes of egress for pulmonary venous return. In classic cor triatriatum, there is an accessory chamber within the left atrium that represents the CPV. This accessory chamber communicates with the left atrium through an opening that demonstrates varying degrees of stenosis. The accessory chamber is always above the level of the left atrial appendage, a finding that allows differentiation of the membrane of cor triatriatum from a supravalvular mitral ring. However, many different variations of this entity may occur. For example, the proximal pulmonary venous chamber may communicate with both the left atrium and the right atrium. Furthermore, some patients have partial cor triatriatum, in which unilateral pulmonary veins drain to the pulmonary venous chamber and thence to the left atrium, while the contralateral pulmonary veins drain anomalously to a systemic vein. Clinical features depend on the exact nature of the communication and the number of involved pulmonary veins. In classic cor triatriatum, features of pulmonary venous obstruction predominate. These include pulmonary hypertension, pulmonary edema, frequent pulmonary infections, failure to thrive, and hemoptysis (Fig 8). Advanced cardiac imaging with CT or MR imaging may be necessary in atypical forms of cor triatriatum in which drainage of all individual pulmonary veins cannot be completely defined with echocardiography. The MR imaging protocol consists of cine SSFP or GRE sequences to provide excellent visualization of intracardiac

10 96 January-February 2012 radiographics.rsna.org Figure 9. Idiopathic pulmonary vein stenosis in a patient with associated congenital heart disease in the form of a double-outlet right ventricle. Volume-rendered MR angiogram (posterior oblique projection) shows severe proximal stenosis (arrows) of both the left and right lower pulmonary veins. Stenosis of the RUPV was also present but is not clearly evident on this projection. LA = left atrium, * = left atrial appendage. Figure 10. Postnatal de novo pulmonary vein atresia in a patient with complex congenital heart disease. (a) Time-resolved gadolinium-enhanced MR angiogram shows contrast material entering the right heart from a left arm injection. There is flow into the right lung (*) but no flow into the left pulmonary artery (arrow). (b) Cine SSFP image shows atresia of the left pulmonary vein (arrow). anatomy, including the cor triatriatum membrane. Gadolinium-enhanced MR angiography is necessary for complete definition of all pulmonary veins. Since shunts are not involved in the typical cor triatriatum, flow analysis and volumetry are generally not useful. The most important piece of information needed for management is the degree of pulmonary venous obstruction, which is determined by the flow gradient across the stenosis and by right ventricular pressures. The former may be estimated with MR imaging by using cine phase-contrast velocity flow mapping, while echocardiography provides an estimate of right ventricular pressure. CT does not provide any additional advantage except in the sick neonate or infant with severe pulmonary venous obstruction, in whom the short imaging time is advantageous. Again, cardiac gating is required to clearly visualize the cor triatriatum membrane and hence radiation exposure increases significantly. Atresia of the CPV Atresia of the CPV is a rare anomaly thought to be due to failure of the CPV to establish connection to the left atrium or to regression of this connection after its establishment. However, this occurs at a later developmental stage than in patients who have TAPVR (after connections to the splanchnic circulation have already regressed). As in TAPVR, there is no connection of the pulmonary veins to the left atrium; however, unlike in TAPVR, the veins do not have a major channel returning to the systemic veins and right atrium.

11 RG Volume 32 Number 1 Vyas et al 97 Figure 11. Postoperative pulmonary vein stenosis after surgical repair of TAPVR. (a) Volume-rendered MR angiogram (posterior projection) shows severe diffuse stenosis of all left pulmonary veins (arrow). There is a focal stenosis of the right pulmonary veins at the entrance to the left atrium. The more peripheral branches of the right pulmonary veins are dilated due to obstruction. (b) Bright-blood MR image shows severe narrowing of the left lower pulmonary vein (arrow). The right lower pulmonary vein appears to be of normal caliber. LA = left atrium, LV = left ventricle, RA = right atrium, RV = right ventricle. Owing to lack of any effective egress of pulmonary venous blood, the pulmonary veins are usually underdeveloped. Often, true pulmonary veins may not be clearly demonstrated. Small collateral veins serve to decompress small amounts of pulmonary venous blood to other systemic venous channels. The condition generally manifests in the neonatal period as extreme cyanosis from pulmonary venous obstruction. The disorder is often fatal, and surgical palliation is difficult due to absence of well-developed pulmonary veins. Results of echocardiography are typically inconclusive because no pulmonary venous return (either to the left atrium or to systemic veins and the right atrium) can be demonstrated. Thus, advanced imaging may be needed. However, such imaging is difficult and hazardous because the neonate is usually in extremis. Diagnosis hinges on demonstration of absence of developed pulmonary venous structures. Given the rarity of this anomaly and the degree of cardiorespiratory compromise, it is unusual that MR imaging may be needed or clinically feasible. Nongated CT angiography may be the diagnostic modality of choice for confirming the diagnosis, if needed. Congenital Stenosis or Atresia of Individual Pulmonary Veins The embryologic basis of congenital stenosis or atresia of an individual pulmonary vein is unclear. Anatomically, there is localized or diffuse hypoplasia, focal stenosis, or atresia of one or more pulmonary veins. Three potential clinical settings in which this condition may be found are (a) in isolation, (b) in association with congenital heart disease (Figs 9, 10), and (c) after surgery for repair of anomalous pulmonary veins (Fig 11). The clinical presentation depends on the number of involved veins and the degree of pulmonary venous obstruction. Stenosis of a single pulmonary vein is generally well tolerated. With stenosis of all veins of one lung, there may be redirection of pulmonary arterial flow to the opposite lung. Pulmonary hypertension may occur. Bilateral pulmonary vein stenosis is poorly tolerated and is characterized by recurrent pulmonary infections, failure to thrive, hemoptysis, and pulmonary hypertension. It is difficult to definitively diagnose stenosis of individual pulmonary veins with echocardiography alone, particularly beyond the neonatal

12 98 January-February 2012 radiographics.rsna.org period. Thus, definitive imaging with MR imaging or CT is generally required. MR angiography and CT angiography both show pulmonary veins well, but CT does have better spatial resolution. However, gadolinium-enhanced MR angiography is usually diagnostic and MR imaging provides additional functional information, such as pulmonary vein flow dynamics and differential pulmonary arterial flow. Variation in the Number of Pulmonary Veins Most individuals have four pulmonary veins (two right, two left). Sometimes a single pulmonary vein may be present on one side (more commonly on the left than the right). Occasionally, there may be three or more pulmonary veins on one side. These variations may be incidentally seen at imaging performed for another reason and have no functional significance. Conclusions We have briefly reviewed common congenital pulmonary vein anomalies, their embryologic bases and clinical features, and information desired from advanced imaging study. MR imaging and CT are methods of choice for demonstration of congenital pulmonary vein anomalies when echocardiography does not provide the necessary data. In most patients, MR imaging provides precise anatomic and functional data without use of ionizing radiation. CT offers better spatial resolution at the expense of exposure to ionizing radiation. The rapid nature of CT is useful in critically ill neonates and infants with TAPVR. References 1. Geva T, Praagh SV. Anomalies of the pulmonary veins. In: Allen HD, Driscoll DJ, Shaddy RE, Feltes TF, eds. Moss and Adams heart disease in infants, children, and adolescents: including the fetus and young adults. 7th ed. Philadelphia, Pa: Lippincott Williams & Wilkins, 2008; Tsai-Goodman B, Geva T, Odegard KC, Sena LM, Powell AJ. Clinical role, accuracy, and technical aspects of cardiovascular magnetic resonance imaging in infants. Am J Cardiol 2004;94(1): Edwards JE. Pathologic and developmental considerations in anomalous pulmonary venous connection. Proc Staff Meet Mayo Clin 1953;28(17): Greil GF, Powell AJ, Gildein HP, Geva T. Gadolinium-enhanced three-dimensional magnetic resonance angiography of pulmonary and systemic venous anomalies. J Am Coll Cardiol 2002;39(2): Alsoufi B, Cai S, Van Arsdell GS, Williams WG, Caldarone CA, Coles JG. Outcomes after surgical treatment of children with partial anomalous pulmonary venous connection. Ann Thorac Surg 2007; 84(6): ; discussion Neill CA, Ferencz C, Sabiston DC, Sheldon H. The familial occurrence of hypoplastic right lung with systemic arterial supply and venous drainage scimitar syndrome. Bull Johns Hopkins Hosp 1960;107: Beerbaum P, Körperich H, Barth P, Esdorn H, Gieseke J, Meyer H. Noninvasive quantification of left-to-right shunt in pediatric patients: phasecontrast cine magnetic resonance imaging compared with invasive oximetry. Circulation 2001;103(20): Mooij CF, de Wit CJ, Graham DA, Powell AJ, Geva T. Reproducibility of MRI measurements of right ventricular size and function in patients with normal and dilated ventricles. J Magn Reson Imaging 2008; 28(1): Khan MA, Torres AJ, Printz BF, Prakash A. Usefulness of magnetic resonance angiography for diagnosis of scimitar syndrome in early infancy. Am J Cardiol 2005;96(9): Riesenkampff EM, Schmitt B, Schnackenburg B, et al. Partial anomalous pulmonary venous drainage in young pediatric patients: the role of magnetic resonance imaging. Pediatr Cardiol 2009;30(4): Van Praagh S, Carrera ME, Sanders SP, Mayer JE, Van Praagh R. Sinus venosus defects: unroofing of the right pulmonary veins anatomic and echocardiographic findings and surgical treatment. Am Heart J 1994;128(2): Valente AM, Sena L, Powell AJ, Del Nido PJ, Geva T. Cardiac magnetic resonance imaging evaluation of sinus venosus defects: comparison to surgical findings. Pediatr Cardiol 2007;28(1): Fenchel M, Greil GF, Martirosian P, et al. Threedimensional morphological magnetic resonance imaging in infants and children with congenital heart disease. Pediatr Radiol 2006;36(12): Sørensen TS, Körperich H, Greil GF, et al. Operator-independent isotropic three-dimensional magnetic resonance imaging for morphology in congenital heart disease: a validation study. Circulation 2004;110(2): Van Praagh S, Carrera ME, Sanders S, Mayer JE Jr, Van Praagh R. Partial or total direct pulmonary venous drainage to right atrium due to malposition of septum primum: anatomic and echocardiographic findings and surgical treatment a study based on 36 cases. Chest 1995;107(6): Tomar M, Radhakrishnan S, Shrivastava S. Partial or total anomalous pulmonary venous drainage caused by malposition of septum primum: echocardiographic description of a rare variant of anomalous pulmonary venous drainage. J Am Soc Echocardiogr 2005;18(8):884. This journal-based CME activity has been approved for AMA PRA Category 1 Credit TM. See

13 Teaching Points January-February Issue 2012 MR Imaging and CT Evaluation of Congenital Pulmonary Vein Abnormalities in Neonates and Infants Himesh V. Vyas, MD S. Bruce Greenberg, MD Rajesh Krishnamurthy, MD RadioGraphics 2012; 32:87 98 Published online /rg Content Codes: Page 88 With its excellent safety profile and ability to provide anatomic and physiologic information, it is easy to see why MR imaging is the method of choice for delineation of pulmonary vein abnormalities (2). Page 88 One exception is the case of a pulmonary venous obstruction in a newborn infant with inconclusive findings at echocardiography. In this situation, a lengthy MR imaging examination is not desirable, and urgent definition of pulmonary venous anatomy is best achieved by means of ungated CT angiography without use of sedation. Page 90 In most neonates with TAPVR, complete anatomic delineation of the defect is possible with echocardiography alone. However, in certain situations patients may need more advanced imaging with MR imaging or CT. Page 93 The amount of left-to-right shunting is quantified with cine phase-contrast flow analysis of the aorta and main pulmonary artery to estimate the Qp/Qs ratio. Page 94 Indications for MR imaging include an unclear diagnosis or incomplete definition of involved pulmonary veins at echocardiography. In most cases, acquisition of functional information such as shunting and volumes typically is not clinically necessary, since the defect is almost always large and unrestrictive and the diagnosis alone is an indication for intervention.