Practice

Teaching Case Report Most physicians are generally familiar obstetrical weeks), an innominate vein with the normal SVC and its tributaries. forms between the 2 SVCs. Unusual variation in upper- Blood from the head and neck travels By the twelfth week of fetal age, the via the external and internal jugular left SVC is normally obliterated and only body venous anatomy found veins, which join the subclavian veins to the right SVC remains (Fig. 3, centre pa- form the right and left brachiocephalic nel). The coronary sinus, which collects with cardiovascular MRI veins. These in turn empty through a myocardial venous blood, develops right-situated SVC into the right atrium. from the left common caval vein, initial- Case: As part of a general presurgical As embryos, however, our venous ly connected to the left superior and in- evaluation, a 42-year-old man under- system is very different (Fig. 3, left ferior vena cavae. This explains why the went radiography (Fig. 1). His chest panel). During the sixth week of devel- vein is connected to the coronary sinus radiograph showed mild cardiomegaly opment, the primary atrium receives in most cases of persistent left SVC. In and enlargement of his superior medi- venous tributaries from both sides of rare instances there is involution of the astinum. Cardiovascular MRI to assess the embryo through the common car- right SVC along with persistence of the his thoracic aorta and left-ventricular dinal (caval) vein, which connects the left (Fig. 3, right panel). function revealed a mildly dilated left paired superior (which drain the cran- It is not uncommon to find patients ventricle with normal systolic function, ial parts) and inferior caval veins with a persistent left SVC draining into but also a coronary sinus (normally (which drain the caudal parts). When the coronary sinus along with a normal < 1.5 cm across) dilated to 4.5 × 2.7 cm we are only 8 weeks old (at around 10 right SVC; this occurs in 0.3% of the in cross-section (Fig. 2A). The cause of this severe dilatation was found to be a left-sided (SVC) connected to the coronary sinus (Fig. 2B). The right SVC was absent; blood from the upper part of his body was transported to the right atrium through the left SVC by way of the coronary si- nus (Fig. 2B,D). His thoracic aorta was of normal size; no other cardiovascular abnormalities were found. The surgical team was informed of the findings, and the patient’s knee-ligament surgery was successful.

Fig. 2: Cardiovascular MRI, “bright blood” sequence. A. Scan of the cardiac 2-chamber plane: the coronary sinus is severely dilate. B. Thoracic : the left SVC (ar- row) is connected to the cardiac sinus (star) and the left azygos vein (arrowhead) drains into the left SVC. C. Transverse plane through the upper : the left SVC (star) and 6 6

1 Fig. 1: Chest radiograph, posteroante- left azygos vein (arrowhead) are evident, whereas the right SVC is absent. D. Coronal 0 6 0

. rior view. The vascular shadow (arrow) thoracic plane: The innominate vein (arrowhead) connects the right jugular and subcla- j a

m in the upper , extending vian veins to the left SVC (arrow). Ao = ascending thoracic aorta, DAo = descending c /

3 thoracic aorta, LA = left atrium, LL = left , LSVC = left-sided superior vena cava, LV 0 from the clavicle along the left margin 5 1 . of the aortic arch, reveals the left-sided = left ventricle, PA = , RL = right lung, SVC = superior vena cava, VB = 0 1 : I superior vena cava. vertebral body. O D

CMAJ • July 4, 2006 • 175(1) | 27 © 2006 CMA Media Inc. or its licensors Practice

Box 1: Malformations associated with persistent left superior vena cava (SVC)

Although no specific pattern of association has been demonstrated, 46% of patients with left- sided superior vena cava (SVC) have other malformations. The bulleted conditions below are generally detected during fetal life or at birth; dashed malformations are less apparent, although they may become symptomatic during adult life: % — Atrial septal defect 16 • Complete or partial common AV canal 11 Fig. 3: The development of persistent left-sided superior vena cava (SVC). Left panel: The embryonic venous system, in which the superior and inferior • Tetralogy of Falot 9 caval veins (CVs) join into the common caval vein. At 8 weeks, the innomi- • Coarctation of the aorta 7 nate vein links the superior CVs. Centre: The left superior CV normally oblit- — Unroofed coronary sinus 7 erates distally to the innominate vein; the right-sided SVC develops from the — Partial anomalous pulmonary venous right superior CV and part of the right common CV. The coronary sinus, connection 1 which collects myocardial venous blood, develops from the left common CV. When persistent left SVC is discovered in an Right panel: A persistent left SVC connects to the coronary sinus. The right- asymptomatic patient, make sure to rule out sided SVC is absent because of persistence of the distal superior CV segment associated malformations, especially those that on the left and involution on the right. AntCV = superior caval veins, CCV = are less apparent. common caval vein, CS = coronary sinus, InV = innominate vein, LSVC = left- Note: AV = atrioventricular. sided superior vena cava, PostCV = inferior caval veins.

general population and is considered a imation of our patient’s anatomy, see and unlimited imaging plane selection, normal variant of systemic venous re- Appendix 1 (available at www.cmaj.ca is better suited to make the diagnosis turn.1 In such patients, blood from the /cgi/content/full/175/1/27/DC1). than transthoracic echocardiography. left jugular and subclavian veins reaches Adult patients with a persistent left In the absence of associated cardio- the right atrium via a left SVC and the SVC are often identified either inciden- vascular malformations, this condition coronary sinus while the right brachio- tally when a patient is imaged for other is clinically asymptomatic. cephalic vein drains into the normal purposes (e.g., a widened mediastinum right SVC. However, it is fairly rare to noticed on a chest radiograph, as in the Constantin B. Marcu find a patient such as ours, with a per- case we describe here, or a dilated coro- Aernout M. Beek sistent left SVC in the absence of a nary sinus seen via routine echocardio- Albert C. van Rossum right-sided SVC and with normal vis- graphy, cardiovascular MRI or CT) or Department of Cardiology ceroatrial orientation (situs solitus), when the insertion of a pacemaker or a Vrije University Medical Center which occurs in less than 0.1% of the pulmonary-artery catheter proves diffi- Amsterdam, The Netherlands general population.2 Nearly half of pa- cult. Advancement of such devices tients with left SVC (46%) have associ- through the left SVC and coronary si- Competing interests: None declared. ated congenital abnormalities (Box 1), nus may lead to vessel-wall injury or which are often significant enough to knotting in the right atrium.2 be detected before or just after birth. In such cases, other associated mal- REFERENCES However, half of patients with a persist- formations such as an atrial septal de- 1. Edwards J, DuShane J. Thoracic venous anomalies. ent left SVC and absent right SVC are fect or anomalous pulmonary venous Arch Pathol 1950;49:517-37. 2. Bartram U, Van Praagh S, Levine JC, et al. Absent asymptomatic and have no associated return should be ruled out. Cardiovas- right superior vena cava in visceroatrial situs soli- cardiac malformations. For an MRI an- cular MRI, with its large field of view tus. Am J Cardiol 1997;80:175-83.

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