Congenital Anomalies of the Superior Vena Cava: A CT Study

By Mary G. Cormier, Joseph W. Yedlicka, Richard J. Gray, and Rogelio Moncada

T HE PRECISE and elegant rendering of the human anatomy achieved by CT has, for

over a decade, provided a novel perspective to the medical diagnostic armamentarium. CT has had a significant impact on almost every avenue in the daily practice of medicine and has gained broad acceptance by our clinical colleagues.

A wide variety of congenital vascular anoma- lies of the upper mediastinum exist. Since most of these are clinically silent, they are often unsus- pected and discovered incidentally on radio- graphic studies done for other reasons. Familiar- ity with the CT appearance of such anomalies may aid in the interpretation of otherwise poten- tially confusing CT images.

Innovative techniques for solving clinical prob- lems have been designed. Some have improved our diagnostic capabilities, while others have introduced interventional techniques that offer therapeutic and palliative alternatives to surgery. CT has had a significant impact on just about every avenue in the daily practice of medicine. Its broad acceptance by our clinical colleagues and the documented direct benefit to the patient crown a historical decade of medical imaging progress.

ANATOMIC CONSIDERATIONS

The normal SVC is devoid of venous valves; it drains the returning blood flow of the head and upper half of the trunk. The vessel measures approximately 7 cm in length. Its cross-sectional shape varies in proportion to its intraluminal flow or pressure, and generally exhibits an oblong, flat, or rounded contour; the latter more often seen when the patient is examined during a Valsalva maneuver. The caliber of the SVC varies, but generally is 1.5 cm and rarely as much as 2.0 cm at its greatest diameter.

The short and vertically oriented right bra- chiocephalic vein and its longer oblique counter- part on the left form the origin of the SVC at the level of the first right costal cartilage. From this point, the SVC descends vertically along the right side of the mediastinum to end in the upper part of the right atrium at the level of the right third costal cartilage. In its descent it describes a minimal convexity to the right. Its lower half is covered by the parietal pericardium and its wall

is partially composed of visceral pericardium. The major tributary of the SVC, the azygos vein, enters the dorsal aspect of the mid-SVC.

Ventrally, the SVC is related to the mediasti- nal fat, pleura, thymus, and adjacent right lung. Caudally, it is overlapped at the left margin of its intrapericardial portion by the ascending aorta. The SVC is related posteriorly to the innominate artery, trachea, right main bronchus, right main pulmonary artery, right superior pulmonary vein, and vagus nerve. In addition, the SVC is flanked by a large number of adjacent lymph nodes; most of these occur along the dorsal aspect.

EMBRYOLOGY

The embryo has a closed blood circuit by the end of the second week of fetal development. By the third or fourth week, two paired venous trunks are formed: the anterior cardinal veins, arising from the cranial part of the body, and the posterior cardinal veins, arising from the caudal part of the body. On each side of the heart the ipsilateral anterior and posterior cardinal veins unite into a short main trunk called the common cardinal vein or duct of Cuvier. Each duct of Cuvier in turn empties into the sinus venosus.’

ABBREVlATlONS

ASD, atrial septal defect

IVC, inferior vena cava PDA, patent ductus arteriosus

RA, right atrium SVC, superior vena cava

VSD, ventricular septal defect

From the Department of Radiology. Loyola University

Medical Center, Maywood, IL and the Department of Radi- ology. University of Minnesota, Minneapolis.

Mary G. Cormier: Assistant Professor, Department of Radiology, Dartmouth-Hitchcock Medical Center, Hanov- er. NH; Joseph W. Yedlicka: Fellow, Department of Radiol-

ogy, University of Minnesota; Richard J. Gray; Rogelio Moncada: Professor and Chairman, Department of Radiolo-

gy, Loyola University Medical Center. Address reprint requests to Mary G. Cormier, MD,

Department of Radiology, Dartmouth-Hitchcock Medical

Center. Hanover, NH 03756. o I989 by W.B. Saunders Company. 0037- I98X/89/2402-0003$5.00/O

Seminars in Roentgenolow. Vol XXIV, No 2 (April), 1989: pp 77-83 77

CORMIER ET AL

Normally, as the heart descends caudally, a wide transverse anastomosis forms between the two anterior cardinal veins; this channel becomes the left innominate vein, presumably derived from the union of smaller thyroid or thymic branches of the primitive jugular veins.2 The segment of the right anterior cardinal vein that lies caudal to this anastomosis, together with the right common cardinal vein (right duct of Cuvier), forms the primitive SVC.’

At this stage a left SVC also exists, similarly formed by the corresponding segment of the left anterior cardinal vein that lies caudal to the primitive left innominate vein, and the left com- mon cardinal vein (left duct of Cuvier). A major portion of this left SVC undergoes atrophy dur- ing the following few weeks. Its cranial remnant forms the trunk of the first left intercostal vein, and its caudal remnant becomes the oblique vein of the left atrium.’ In some cases the involuted vessel remains as a few fibrous strands or as a fibrous cord that attaches to the posterolateral aspect of the pericardium and coronary sinus, referred to as the oblique ligament of Marshall.2

The sinus venosus is oriented transversely, lies dorsal to the undivided atria1 part of the heart, and communicates with the single common atria1 chamber through an oval opening. Its lateral portions, known as horns, become directed upward and posteriorly as the heart descends into the thorax. By approximately 4 to 5 weeks the symmetric arrangement is lost. The sinoatrial opening migrates to the right, and an atria1 septum is formed in such a manner that the sinus venosus communicates only with the right atria1 chamber. Eventually the left horn of the sinus venosus becomes the coronary sinus. The right horn expands, receiving blood from the SVC and future IVC, and ultimately is totally absorbed into the wall of the right atrium.‘*3v4

Many anomalies of the SVC are known, each representing some form of developmental arrest. The basic abnormality is failure of the left ante- rior cardinal vein to involute normally, resulting in persistence of a left SVC.

LEFT SUPERIOR VENA CAVA

The sign of a left SVC, either alone or in conjunction with a right SVC, depends upon resultant hemodynamic effects. Approximately 75% of both double SVC and single left SVC are asymptomatic and have no circulatory distur-

bance. However, in the remainder significant dysfunction may exist, possibly severe enough to be incompatible with life.4

Incidence

The true overall incidence of this condition is difficult to establish. Estimates ranging from 1 per 330 to 1 per 750 normal individuals, and 1 per 25 patients with congenital heart disease are reported.4 Among these, a coexisting right SVC is present in about 85%.5

Anatomic Relations

When a double SVC exists, the left SVC descends vertically, anterior and to the left of the aortic arch and main pulmonary artery, slightly lateral to the left vagus nerve. It has been said by some to course between the left pulmonary artery and pulmonary veins, and by others to lie ante- rior to all of the left pulmonary vessels. The latter position corresponds to that of the right SVC relative to the right pulmonary vessels.

The left SVC then swings medially, pierces the pericardium to run in the posterior atrioventricu- lar groove, and enters the coronary sinus. In this case, the coronary sinus is often abnormally large, perhaps due in part to an increased volume flowing through it, and partially to regurgitant enlargement during atria1 contraction. In approximately 25% of 174 cases of left SVC, Winter2 found the left hemiazygos vein looping over the left main bronchus to enter the left SVC posteriorly, at the same level that the azygos vein enters the right SVC.

When a double SVC exists, the caliber of the right vessel is often normal; however, it may be smaller than usual because of reduced blood volume. The diameter of the left cava rarely exceeds that of the right; it is frequently equal to it or smaller.

Specific Entities

Figure 1 schematically depicts the major pat- terns and types of developmental anomalies of the SVC. The most frequent is a double vena cava, with normal right SVC anatomy and a left SVC entering the coronary sinus, and subse- quently draining into the right ,atrium. There may or may not be a transverse anastomosis between the paired cavas. When there is none, the right and left halves of the head and upper truck drain back to the heart independently, and

CONGENITAL ANOMALIES OF THE SVC: CT STUDY

WC

Normal anatomy

A

-1 : > B

0 rl : :

0 ‘;‘ c :

C

0 0 b-b c : : )

I Vertical Vein Anomalous pulmonary D 1 I Absent Right SVC: Absent Right SVC; venous drainage

to svc. Fusiform aneurysm

of svc. Saccular aneurysm

Of svc.

Fig 1. Schematic depiction of SVC anomalies. SVC, su-

Double SVC; Double SVC; Left SVC to C-S. Len svc to cs.

No venous Venous intercommunication intercommunication

Double SVC; perior vena cava; WC, inferior

Len svc to u. vena cava: CS. coronary sinus; LA, left atrium; RA. right atrium.

Left svCt0 cs.. Left SVC to LA.

the coronary sinus is large, approaching the caliber of the cava entering it (Fig 2).6

When an anastomosis does exist between the two cavas, it may be oriented inferiorly toward the right, inferiorly toward the left, or directed transversely. The relative size of the two cavas and of the coronary sinus depends on the amount of blood each carries as routed above. In some cases, additional cross-communication exists in the form of several small, slender, irregularly branching veins, a plexiform arrangement that Papez7 suggests probably represents the persis- tence of vessels that normally contribute to the formation of the left innominate vein.7

The most frequent cardiac anomaly associated with a left SVC that drains into the RA is an ASD. Gensini et al* noted that a left-to-right shunt at the atria1 level is often present in conjunction with anomalous pulmonary venous drainage into either a left or right SVC. The anomalous drainage in the majority of cases is total. Septal defects always coexist.

Infrequently the left SVC enters the left atrium or the left side of a common atrium. In this case other cardiac anomalies are almost always associated.’

The true incidence of a persistent left SVC with absence of a right SVC is not known, but it

is rare. Functionally, this arrangement results in no circulatory disturbance if the left SVC drains directly or indirectly into the right atrium (Fig 3).

lo-12

A left SVC may be associated with a wide variety of cardiac defects, including single atrium, VSD, PDA, tetralogy of Fallot, truncus arteriosus, pulmonary stenosis or atresia, Ebstein malformation, atrioventricular canal defects, Taussig-Bing complex, mitral atresia, tricuspid atresia, transposition, anomalous pulmonary venous return, and coarctation of the aorta.“2*‘3

There is a higher incidence of left SVC in cases of transposition of the viscera. Campbell and Deuchar’ found a left SVC in 40% of 46 cases of congenital heart disease in which there was also some degree of visceral transposition. A double SVC is more common when visceral transposition is partial than when it is complete. Finally, left SVC is frequently described with asplenia.3,4,‘3

VERTICAL VEIN

Careful distinction should be made between a persistent left SVC and an anomalous left verti- cal vein. The left vertical pulmonary vein that receives partial or total left pulmonary venous drainage, ascends superiorly, usually anterior to

Fig 2. Double SVC with normal right SVC anatomy and the left SVC draining into en enlarged coronary sinus. This patient also had an unrelated incidental finding: hemiazy- gos continuation of a left inferior vena cave. SVC. superior vena ceva; Ao. aorta: MPA. main pulmonary ertery: LPA, left Pulmonary artery; CS, coronary sinus: R. right: L. left: h. hemiazygos vein.

80

Fig 3. Left WC in the absence of a right SVC. The right suparior pulmonary vein should not be mistaken for a right SVC. R In V, right innominate vein: I. In V. left innominate vain: SVC, superior vena cava: Ao, aorta: LPA, left pulmonary arte- ry: RPA, right pulmonary artery: PA. main pulmonary artery: Ft. right: L. left.

82 CORMIER ET AL

the aorta, and drains into the left innominate vein. It is now generally accepted that a true left SVC drains into the heart.13*14

ANOMALIES OF THE RIGHT SUi’ERIOR VENA CAVA

Relatively few intrinsic right SVC anomalies occur. The right SVC rarely drains into the left atrium without any coexisting defects. This cre- ates a right-to-left shunt with cyanosis. Only a handful of cases have been reported.11*‘5*‘6

Freedom et al” reported a case in which the right SVC drained into the RA via a low inser- tion associated with complex congenital heart defects.”

Fig 4. Fusiform aneurysm of superior vena cava. Ao. aorta: SVC superior vena cava aneurysm; PA. pul nary artery.

the an.

Imo-

Congenital aneurysm of the SVC is rare. It is nonetheless important in the differential diag- nosis of a superior mediastinal mass. Two dis- tinct types are recognized: saccular and fusiform. Direct opacification of the vascular lesion, either angiographically or on contrast-enhanced CT, provides the diagnosis (Fig 4). It is generally accepted that because this is a low-pressure system, the aneurysm does not thrombose, enlarge, or rupture, making conservative man- agement appropriate.‘8*19

REFERENCES

1. Kjellberg SR, Mannheimer E, Rudhe U, et al: Diag- nosis of congenital heart disease. Chicago: Year Book Medi- cal, 1959

CONGENITAL ANOMALIES OF THE SVC: CT STUDY a3

2. Winter FS: Persistent left superior vena cava. Survey of world literature and report of thirty additional cases. Angi- ology 1954;5:90-132

3. Campbell M, Deuchar DC: The left-sided superior vena cava. Br Heart J 1954;16:423-39

4. Gray SW, Skandalakis JE: Embryology for Surgeons. Philadephia: Saunders, 1972

5. Webb WR, Gamsu G, Speckman JM, et al: Computed tomographic demonstration of mediastinal venous anomalies. AJR 1982;139:157-61

6. McManus JFA: A case in which both pulmonary veins emptied into a persistent left superior vena cava. Can Med Assoc J 1941;45:261-4

7. Papez JW: Two cases of persistent left superior vena cava in man. Anat Ret 1938;70:191-8

8. Gensini GG, Caldini P, Casaccio F, et al: Persistent left superior vena cava. Am J Cardiol1959;4:677-85

9. Shumacker HB, King H, Waldhausen JA: The persis- tent left superior vena cava. Surgical implications, with special reference to caval drainage into the left atrium. Ann Surg 1967;165:797-805

10. Pugliese P, Murzi B, Aliboni M, et al: Absent right superior vena cava and persistent left superior vena cava: Clinical and surgical considerations. J Cardiovasc Surg

I984;25: 134-7 11. Vasquez-Perez J, Frontera-Izquierdo P: Anomalous

drainage of the right superior vena cava into the left atrium

as an isolated anomaly. Rare case report. Am Heart J 1979;97:89-91

12. Lenox CC, Zuberbuhler JR, Park SC, et al: Absent right superior vena cava with persistent left superior vena cava: Implications and management. Am J Cardiol 1980;45: 1 S7-22

13. Cha EM, Khoury GH: Persistent Left superior vena cava. Radiologic and clinical significance. Radiology 1972;103:375-81

14. Caffey J: Pediatric x-ray diagnosis (ed 7). Chicago: Year Book Medical, 1978

15. Braudo M, Beanlands DS, Trusler G: Anomalous drainage of the right superior vena cava into the left atrium. Can Med Associ J 1968;99:7 15-9

16. Park HY, Summerer MH, Preuss K, et al: Anomalous drainage of the right superior vena cava into the left atrium. / Am Co11 Cardiol 1983;2:358-62

17. Freedom RM, Schaffer MS, Rowe RD: Anomalous low insertion of right superior vena cava. Br Heart J 1982;48:601-3

18. Modry DL, Hidvegi RS, LaFIeche LR: Congenital saccular aneurysm of the superior vena cava. Ann Thorac Surg 1980; 29125862

19. Train JS, Mandel G, Efremidis SC: Fusiform aneu- rysm of the superior vena cava. MZ Sinai J Med 198 1;48: 128- 30