375 Partial Anomalous Pulmonary Venous Drainage of the Left Upper Lobe vs Duplication of the Superior Vena Cava: Distinction Based on CT Findings Evan H. Dillon1 OBJECTIVE. Partial lobe Catharine Camputaro2 and duplication of the superior vena cava have similar appearances on CT scans. The purpose of this study was to review their appearances and provide guidelines for difterentiating between them. MATERIALS AND METHODS. A review of the CT reports for the preceding 4 years disclosed seven patients whose original diagnosis was duplication of the superior vena cava and one patient whose diagnosis was partial anomalous pulmonary venous drainage of the left upper lobe. The 14 CT examinations of these eight patients were reviewed in order to observe the CT findings in each anomaly. RESULTS. In only five of the seven patients whose original diagnosis was duplication of the superior vena cava were CT findings compatible with that diagnosis. In the other two, CT findings were compatible with partial anomalous pulmonary venous drainage of the left upper lobe, as they were in the one patient with that as his original diagnosis. Two CT findings allow consistent differentiation. In duplication of the superior vena cava, two vessels can be seen anterior to the left main bronchus, whereas no vessels are present in this location in partial anomalous pulmonary venous drainage of the left upper lobe. Additionally, careful inspection reveals that the intraparenchymal veins in the left upper lobe drain to the normally positioned left superior pulmonary vein in duplication of the superior vena cava, whereas they drain to the anomalous vessel in upper lobe. CONCLUSION. Careful analysis of the CT scans with particular attention to these two features allows difterentiation between partial anomalous pulmonary venous drainage of the left upper lobe and duplication of the superior vena cava. AJR 1993;160:375-379 Congenital abnormalities of the major mediastinal venous structures occur in less than 2% of persons who have no other abnormalities [1-5]. Although many congenital anomalies have been described, three occur with sufficient frequency that they will be encountered in routine clinical practice: azygos or hemiazygos continuation of an interrupted inferior vena cava, persistence of a left superior vena cava with on without a coexisting right superior vena cava, and partial anomalous pulmonary venous drainage. Although they may occur in adults who have... no other abnormalities, these three abnormalities also may be associated with a Received July 6, 1992; accepted after revision... August25, 1992. wide variety of vascular anomalies and cardiac defects [5-10]. If no other abnor- 1Centrum Radiodiagnostiek, Academisch Ziek- malities are present, only partial anomalous pulmonary venous drainage is, in enhuis Utrecht, Heidelberglaan 100, 3584 cx itself, a pathologic finding. In this anomaly, blood from the anomalously drained Utrecht, the Netherlands. portion of the lung is recirculated to the right side of the heart, creating a left-to- 2Department of Radiology, Yale University night shunt. Significant overlap exists in the CT findings in duplication of the supe- School of Medicine, 333 Cedar St., 2-NF, New.. Haven, CT 06510. nor vena cava and partial 0361-803X/93/1602-0375 lobe, which is reported to be one of the more common types of partial anomalous American Roentgen Ray Society pulmonary venous drainage [2, 6]. This article describes the CT findings in partial
376 DILLON AND CAMPUTARO AJA:160, February 1993 lobe and duplication of the superior vena cava and provides guidelines for differentiating these anomalies. Materials and Methods The CT reports for the preceding 4 years were reviewed. The original diagnosis based on CT findings was duplication of the supenon vena cava in seven patients and partial anomalous pulmonary venous drainage in one patient. A total of 14 chest CT examinations were performed in these eight patients. Eleven were performed with a General Electric 9800 scanner and three with a Philips LX scannen. Bolus injection of IV contrast material was used for all scans. The injection was via the left arm in nine of the 14 examinations. All the CT scans of these eight patients were reviewed. Particular attention was paid to these features: presence of a left innominate vein crossing the mediastinum, presence of an azygos and/or hemiazygos arch, course of the intrapanenchymal veins in the left upper lobe, appearance of the left hilum, size of the coronary sinus, and CT evidence of right ventricular hypertrophy or dilatation. All the CT scans had been obtained for reasons other than the evaluation of any suspected venous abnormality. One patient had CT for evaluation of a cervical aortic arch, and that examination did not include the area below the left hilum. Three-dimensional (3D) reconstruction of the major mediastinal vascular structures of two patients was performed by using the taped CT data in order to provide an easily recognizable projection of the vascular anomalies. An independent 3D system (ISG Technologies, Toronto, Ontario) and a combination of automatic and manual segmentation were used. Results Review of the CT scans in the seven patients whose original diagnosis was duplication of the superior vena cava showed that only five had CT findings compatible with that diagnosis [1, 3, 4] (Fig. 1). In these cases, the right subclavian and jugular veins drained normally to a night superior vena cava, and the left subclavian and jugular veins drained to a left superior vena cava. The left superior vena cava could be seen coursing vertically in the mediastinum lateral to the aortic arch. Three of the five patients with duplication of the superior vena cava had no left innominate vein crossing the mediastinum; two had small left innominate veins (0.4 and 0.6 cm in diameter) (Fig. 2). All five patients had an azygos arch, and one also had a hemiazygos arch. Two vessels were visualized anterior to the left main bronchus at the level of the left hilum. When the lung window settings were used, it was clear that the left upper lobe pulmonary venous tributaries drained to the normally positioned left Superior pulmonary vein, which was located lateral and slightly posterior to the left superior vena cava at this level. Infeniorly, the left superior pulmonary vein entered the left atrium, and the left superior vena cava generally became obscured as it descended posterolateral to the left atrium. In one patient, dynamic contrast-enhanced CT scanning allowed opacification and visualization of the left superior vena cava at this level. Finally, at the lowest level, the coronary sinus was enlarged in all four of the patients in whom this level was Fig. 1.-Dupllcation of superior vena cava. A, Dynamic CT scans obtained to opacity superior vena cava on left side (solid arrows) show persistent superior vena cava lateral to aortlc arch on left side. Anterior to left main bronchus, opacified aberrant vessel can be seen anterior to left superior pulmonary vein (open arrow). Coronary sinus is abnormally large and Is opacified by contrast material (arrowhead). B, 3D reconstruction of CT scans shows course of two superior venae cavae.
AJA:160, February 1993 PARTIAL ANOMALOUS PULMONARY VENOUS DRAINAGE 377 Fig. 2.-Duplication of superior vena cava. CT scan shows small opacified left Innominate vein (arrows) anterior to major arterial structures. scanned. In these four patients, the diameters of the coronary sinus measured 1.1, 1.3, 2.1, and 1.8 cm. No obvious signs of right ventricular abnormality were visible on any of the scans. The CT scans showed a total of three other major congenital vascular abnormalities in two of these five patients. One patient had an interrupted inferior vena cava with azygos continuation as well as a prepancreatic portal vein, and one had a cervical aortic arch with pseudocoanctation. Two of the seven patients whose original diagnosis was duplication of the superior vena cava actually had CT findings compatible with partial anomalous pulmonary venous drainage of the left upper lobe [11] (Fig. 3). In addition, the one patient whose original diagnosis was partial anomalous pulmonary venous drainage of the left upper lobe had findings compatible with that diagnosis. In these three cases, a vertically oriented venous structure was visible in the left side of the mediastinum lateral to the aortic arch. This vessel was, at the level of the arch, identical in size and appearance to that seen in the cases of superior vena cava duplication. However, just below this level, careful inspection showed that the pulmonary veins of the left upper lobe drained to this anomalous vessel. Visualization of this confluence was easier when lung window settings were used (Fig. 4). The anomalous vessel was connected at its cephalic end to a left innominate vein of normal to large size, which drained to the right superior vena cava. More infeniorly, at the level of the left hilum and in obvious contrast to the findings in cases of superior vena cava duplication, neither the normal left superior pulmonary vein nor the aberrant vessel could be seen anterior to the left main bronchus. In two patients, no structure was visible anterior to the bronchus; in the other patient, the left atnial appendage could be seen in this region. In contrast to the findings in duplication of the superior vena cava, the coronary sinus was normal in size: 4, 9, and 8 mm in diameter in these three patients. A normal azygos arch was present in all three patients, and no hemiazygos arch was seen in any of them. Fig. 3.-Partial anomalous pulmonary venous drainage of left upper lobe. A, CT scans show that large left innominate vein (containing a central venous catheter) receives anomalous vessel (solid arrows). Note absence of vessels anterior to left main bronchus and normal size of coronary sinus (open arrow). B, 3D reconstruction of CT scans shows course of aberrant pulmonary vein in left upper lobe draining into left Innominate vein.
378 DILLON AND CAMPUTARO AJR:160, February 1993 These three had no other major vascular abnormalities and no CT evidence of right ventricular abnormality. Discussion A B Duplication of the superior vena cava and partial anomabus pulmonary venous drainage of the left upper lobe are two of the most common major congenital venous abnormalities of the mediastinum. A left superior vena cava occurs in approximately 0.3-0.5% of persons who have no other abnormalities [1, 3, 4, 8]. This left superior vena cava is part of a duplicated superior vena cava in 82-90% of cases [5, 7]. Partial anomalous pulmonary venous drainage of one or more lobes occurs in 0.4-0.7% of individuals who have no other abnormalities [2, 12, 13]. Although partial anomalous pulmonary venous drainage is reported in autopsy series to be slightly more common than duplication of the superior vena cava, the paucity of CT reports describing partial anomalous pulmonary venous drainage suggests that it may frequently be overlooked or misdiagnosed [11, 13]. This observation is supported by the fact that two of the three cases of partial anomalous pulmonary venous drainage of the left upper lobe reported here were initially misdiagnosed as examples of duplication of the superior vena cava. The diagnostic confusion between these two anomalies presumably results from their similar appearances on CT. Both anomalies are characterized by the presence of a vertically oriented anomalous vein lateral to the aortic arch. In duplication of the superior vena cava, this aberrant vein usually conducts blood caudally from the left subclavian and jugular veins to the night atrium via the coronary sinus. In partial lobe, the aberrant vein usually conducts blood cranially from the left upper lobe to the left innominate vein, which then drains into the normally positioned superior vena cava on the right side of the aortic arch. Embryologically, the aberrant vein in both anomalies probably represents a persistent left anterior cardinal vein. Nevertheless, in duplication of the superior vena cava, the vein should be termed a persistent left superior vena cava, whereas in partial anomalous pulmonary venous drainage of the left upper lobe, it should be called a vertical anomalous pulmonary vein, because unlike a persistent left superior vena cava, it does not drain caudally into the coronary sinus [10, 14-16]. Among the major CT findings in these two conditions, two deserve special emphasis: analysis of the course of the parahilar intraparenchymal veins in the left upper lobe and evaluation of the number of vessels anterior to the left main bronchus. The course of the parahilar intraparenchymal pulmonary veins in the left upper lobe can best be appreciated by evaluating images obtained with lung window settings. In upper lobe, these pulmonary veins enter the aberrant vessel at the level of the aorticopulmonary window. In duplication of the superior vena cava, the pulmonary veins in the left upper lobe enter the normally positioned left superior pulmonary vein anterior to the left main bronchus. The number of yessels anterior to the left main bronchus is easily appreciated by using soft-tissue window settings. In persons who have no other abnormalities, only one vessel, the left superior pulmonary vein, is present in this location. In duplication of the superior vena cava, two vessels are present anterior to the left main bronchus, specifically, the left superior pulmonary vein and the more medially located left superior vena cava. In contrast, no vessel is present in this location in patients with partial anomalous pulmonary venous drainage of the left upper lobe, although the left atnial appendage may project into this area as itdid in one of our three cases. Other CT findings may also aid in distinguishing between these two anomalies. A normal to large left innominate vein is seen in the expected position in partial anomalous pulmonary venous drainage of the left upper lobe [2, 6, 12, 16]. This vessel is usually absent or small in duplication of the superior vena cava, but a left innominate vein of normal size can occur in up to 20% of cases [5]. Therefore, although the absence of a left innominate vein is a reliable indicator of duplication of the superior vena cava, visualization of this vein does not aid in differentiation. The coronary sinus appears normal in partial anomalous pulmonary venous drainage of the left upper lobe but is usually enlarged in duplication of the superior vena cava, as it receives the Fig. 4.-Partial anomalous pulmonary venous drainage of left upper lobe. A, CT scan displayed with soft-tissue window settings shows aberrant vessel (arrow) anterior to left pulmonary artery. B, CT scan displayed with lung window settings shows small Intraparenchymal veins in left upper lobe (arrow) draining to aberrant vessel.
AJR:160, February 1993 PARTIAL ANOMALOUS PULMONARY VENOUS DRAINAGE 379 blood flow from the left subclavian and jugular veins [1, 4, 5]. However, if a left innominate vein is present in patients with duplication of the superior vena cava, a smaller volume of blood courses through the coronary sinus, and the sinus may be more normal in appearance. Additionally, in duplication of the superior vena cava, the coronary sinus can be opacified by injection of contrast material into the left arm. Visualization of this opacification can be accomplished by dynamic scanning of the chest, as was performed in one of our cases, or the opacification may be seen incidentally on the more cephalic scans in abdominal CT, as occurred in two of our other cases. Recognition of partial anomalous pulmonary venous drainage of the left upper lobe and differentiation from duplication of the superior vena cava is clinically important in sevenal situations. First, especially when associated with a septal defect, the left-to-right shunt of partial anomalous pulmonary venous drainage may be responsible for clinical symptoms [2, 9, 1 5]. In other situations, previously asymptomatic partial anomalous pulmonary venous drainage of the left upper lobe could become symptomatic if the right lung becomes functionally impaired as a result of lung disease or surgery [2]. A right pneumonectomy performed for other reasons could have disastrous results in a patient with partial lobe. In that situation, the shunt volume would dramatically increase to approximately 50% of total pulmonary blood flow, and only the left lower lobe would be contributing to the systemic oxygen supply. In such situations, surgical cornection of the anomalous drainage, as has been described in previous reports, would be necessary [9, 1 5, 16]. Recognition of either of these anomalies can also explain otherwise bizarre chest film appearances. Either may simulate a mediastinal mass or account for an unusual course of a central venous catheter. Because the anomalous vein in upper lobe terminates in small pulmonary veins, advancing a catheter into this vein could cause perforation or thrombosis of its smaller tributaries. Additionally, because the left upper lobe does not drain into the left atrium in partial anomalous pulmonary venous drainage of the left upper lobe, the congestion and edema of left-sided heart failure in such patients would spare the left upper lobe. Likewise, right-sided heart failure could cause otherwise unexplainable pulmonary edema isolated to the left upper lobe. In conclusion, duplication of the superior vena cava and upper lobe have somewhat similar appearances on CT scans, but their clinical significance is very different. Careful analysis of CT scans will allow differentiation between these two anomalies. REFERENCES 1. Cormien MG, Yedlicka JW, Gray AJ, Moncada A. 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