Double superior vena cava and anomalous left atrial drainage of persistent left SVC: A case report

Abstract

Persistent left superior vena cava (PLSVC) is an uncommon developmental variation of the thoracic venous system, sometimes accompanied by a duplicated superior vena cava (SVC). While often asymptomatic when draining into the right atrium, drainage toward the left atrium could lead to a right-to-left shunt and potential compromise of whole-body oxygen delivery. This report describes a 48-year-old male patient with hypertension and chronic tobacco use who was evaluated for dyspnea and leg edema. Imaging revealed a double SVC, where the left-sided vessel connected directly to the left atrium. Despite this anomaly, the patient exhibited no significant hypoxemia or cyanosis, likely due to long-term compensatory mechanisms. This report underscores the need to consider vascular anomalies in imaging interpretation, particularly when findings are incidental. It also underscores the role of contrast-enhanced CT in identifying rare anatomical variants and the potential for such anomalies to remain clinically silent despite physiological significance.

Introduction

The superior vena cava (SVC), a major vein of the upper systemic blood flow, facilitates the return of deoxygenated blood from the cranial, cervical, and superior limb regions to the right atrium (RA) [1]. Under normal circumstances, venous drainage from the right side occurs via the right brachiocephalic vein, while the left side drains through the left brachiocephalic vein [2]. Occasionally, a rare vascular variation known as a duplicated SVC may be present, characterized by a persistent left-sided SVC. This anomaly is estimated to affect approximately 0.3-0.5 percent of the overall population [3].

Persistent left superior vena cava (PLSVC) is acknowledged as a rare venous anomaly that usually remains asymptomatic and is often detected incidentally. The condition is typically recognized during imaging examinations or procedures performed for unrelated purposes, such as chest computed tomography (CT) angiography in pulmonary or cardiovascular examination, or during the placement of central venous catheters and pacemaker leads [4,5].

Embryologically, PLSVC results from the persistence of the left anterior cardinal vein, that ordinarily regresses throughout fetal growth. The left SVC most often connects to the coronary sinus, providing venous drainage to the RA, but in rare cases it may connect directly to the left atrium (LA), causing a right-to-left shunt [6]. Such left atrial drainage is estimated to occur in roughly 10-20 percent of PLSVC cases, representing a clinically significant minority of presentations [7]. This developmental anomaly can occur alone or in association with other cardiovascular malformations, including those within the heterotaxy spectrum [4]. Here, we present a case of double SVC with the left-sided vessel draining into the LA, incidentally identified during contrast-enhanced CT performed for pulmonary evaluation.

Case presentation

A 48-year-old man with hypertension was evaluated in the emergency department following complaints of dyspnea and bilateral lower extremity edema. On presentation, upon examination, the patient's vital parameters included a BP of 138/86 mmHg, HR of 96 bpm, a temperature of 36.9°C, RR of 28 breaths/min, and an O2 saturation of 94%. The physical assessment indicated elevated jugular venous pressure and bilateral pitting edema (grade 2+) of the lower extremities, accompanied by mild scrotal edema and normal heart sounds without any audible murmur.

The patient had a history of cigarette smoking for at least 30 years at a rate of 1 pack per day and was also an opium addict. He denied any history of alcohol use. The patient was on amlodipine 5 mg once daily and was not taking any other medications. He had no history of previous surgeries, no known family history of cardiovascular or genetic diseases, and no notable medical history during the prenatal, perinatal, or childhood periods. All laboratory studies were within normal limits, with the exception of a mildly elevated hemoglobin of 17.2 g/dL (normal range: 13.5-17.0 g/dL) and hematocrit of 51% (normal range: 40%-49%).

Upon arrival, the patient was started on supplemental oxygen, cardiac monitoring was initiated, and a 12-lead electrocardiogram (ECG) was performed, which revealed a normal sinus rhythm without any abnormalities. After the patient was stabilized, a chest X-ray was taken, revealing no significant findings. For further evaluation, the patient underwent a chest computed tomography (CT) scan with a pulmonary thromboembolism (PTE) protocol, which showed no evidence of acute or subacute pulmonary embolism, no radiologic signs of chronic thromboembolic pulmonary hypertension, and no signs of chronic lung disease such as emphysema, bronchial wall thickening, or fibrosis related to long-term smoking. Unexpectedly, the CT scan uncovered a striking vascular anomaly: a double superior vena cava (DSVC), with the PLSVC coursing anomalously to drain into the LA, thereby establishing a potential right-to-left shunt (Fig. 1). Transthoracic echocardiography demonstrated a dilated right ventricle (RV) and RA with severe RV systolic dysfunction. The left ventricular ejection fraction (LVEF) was preserved at 50%, and evidence of pulmonary hypertension was noted. The patient was discharged and scheduled for a follow-up visit in the outpatient clinic for blood pressure adjustment and monitoring. Since then, he has remained stable, with no reported issues (Fig. 2).

Fig. 1.

A rare case of double superior vena cava (SVC) identified on contrast-enhanced CT performed using a pulmonary thromboembolism (PTE) protocol. (A) The right SVC is opacified and drains normally into the right atrium. (B) In contrast, the left SVC anomalously drains into the left atrium, representing a rare congenital vascular variant.

Fig. 2.

Contrast-enhanced chest CT with pulmonary thromboembolism (PTE) protocol demonstrating the anomalous venous drainage. (A) Coronal reconstruction and (B) sagittal reconstruction. The red arrows indicate the left superior vena cava (LSVC), and the yellow arrows identify the left atrium (LA).

Discussion

The development of the thoracic venous system is governed by a series of bilateral transformations and regressions during early embryogenesis. Initially, the anterior cardinal veins are bilaterally symmetrical and function to return deoxygenated blood from the cephalic region of the embryo. As the embryo matures, an anastomotic channel typically forms between these paired anterior veins. This interconnection subsequently evolves into the left brachiocephalic vein, facilitating the shift of cranial venous return to the right side. Concomitant with this reorganization, the caudal segment of the left anterior cardinal vein, along with the left common cardinal vein, normally regresses. The right anterior cardinal vein, in conjunction with the right common cardinal vein, ultimately contributes to the formation of the mature SVC. However, failure of the left-sided venous structures to involute leads to the PLSVC [8,9]. This congenital anomaly arises from the continued patency of the left anterior and common cardinal venous channels. While this anatomical variant generally routes blood to the coronary sinus, it may on infrequent occasions terminate in the LA, creating a direct venous conduit that bypasses the pulmonary circulation. Such aberrant drainage can result in a right-to-left shunt with potential clinical implications, particularly if undetected. The presence of residual embryonic structures, such as the oblique vein of the LA and associated fibrous remnants, further reflects the incomplete regression of the primitive left-sided venous system [3,[8], [9], [10], [11]].

The pathological importance of a PLSVC is largely contingent upon its drainage pattern and any associated cardiac anomalies. When the anomalous vein terminates in the coronary sinus and ultimately into the right atrium, it usually carries little to no clinical consequence and remains silent throughout life [12,13]. However, in rare instances where the left SVC terminates in the LA, it introduces a direct venous-to-arterial shunt, permitting systemic venous blood to bypass pulmonary circulation. This anatomical deviation may result in varying degrees of systemic desaturation, paradoxical embolism, or even complications during diagnostic and therapeutic procedures such as central line placement or cardiac surgery [13,14].

In the case presented, although the anomalous vessel emptied directly into the LA, an arrangement that typically carries a risk of arterial hypoxemia, the patient exhibited no cyanosis or symptoms of desaturation. His oxygen saturation on room air remained within acceptable limits (94%), which is noteworthy considering his extensive smoking history of more than 3 decades. Chronic tobacco exposure can lead to compensatory physiological adaptations such as secondary polycythemia and increased baseline ventilation that may partially offset mild hypoxemia. In patients with a PLSVC draining into the LA, subtle right-to-left shunting can occur when a small volume of systemic venous blood bypasses the pulmonary circulation. The severity of hypoxemia is influenced by the size of the abnormal vessel, the balance of venous return between the right and left SVCs, and the presence or absence of a venous bridge (left brachiocephalic vein). When no bridging vein is present, as in our case, venous return through the left SVC is directed more completely into the LA, increasing the likelihood of a minor shunt and mild oxygen desaturation [4]. Therefore, the patient’s mild hypoxemia was most likely multifactorial, reflecting the combined effects of a limited right-to-left shunt through the LSVC–left atrial connection and chronic smoking–related adaptive changes rather than pulmonary disease alone.

A classification has been developed to describe the morphological variations of DSVC. Zhang et al. [15] introduced a comprehensive CT-based scheme that categorizes DSVC into 4 types according to the presence of a bridging vein (left brachiocephalic vein) and the drainage pathway of the left SVC. In this classification, Types I and II correspond to left SVC drainage into the coronary sinus, with the bridging vein absent in Type I and present in Type II, whereas Types III and IV involve left SVC drainage directly into the LA, without and with a bridging vein, respectively. Based on CT imaging characteristics, specifically the absence of a venous bridge and the direct termination of the left SVC into the left atrium, this case appears most compatible with a Type III configuration; however, a definitive classification would require further evaluation, including assessment of coronary sinus integrity with an echocardiographic bubble study.

The drainage of the left SVC into the LA can occur through different anatomic routes. In the direct type, the LSVC opens directly into the LA, creating a true right-to-left shunt. In the indirect type, drainage occurs through an unroofed coronary sinus, in which the wall separating the coronary sinus from the LA is partially or completely absent, allowing venous blood to enter the LA [4]. A third, complex variant known as Raghib syndrome involves a combination of PLSVC-to-LA connection, an unroofed coronary sinus, and an atrial septal defect. Each configuration has distinct embryologic origins and varying degrees of shunt physiology [16]. In our case, the LSVC drained directly into the LA without communication through the coronary sinus or associated septal defect, representing the simple or direct form of LSVC-to-LA drainage.

In patients with PLSVC draining into the LA, echocardiography with agitated saline contrast injection (bubble study) can serve as a valuable adjunctive tool for confirming anomalous venous return. When the saline is injected into a left arm vein, the immediate appearance of microbubbles within the LA, bypassing the right heart chambers, demonstrates a right-to-left shunt and provides functional confirmation of the drainage pathway [17]. This method is particularly useful when CT or MR findings are inconclusive or when functional assessment of shunting is clinically relevant [4]. However, in our case, a bubble study was not performed because contrast-enhanced CT imaging clearly delineated the anomalous venous connection and provided definitive anatomic confirmation.

In comparison with similar cases, Bitar et al. [18] presented a case of a 19-year-old female with right SVC agenesis and a PLSVC draining directly into the LA through a completely unroofed coronary sinus, accompanied by severe mitral regurgitation that required surgical correction. In contrast, our patient presented with a SVC, with the left SVC draining directly into the LA and the right SVC maintaining normal drainage to the RA. Unlike the case described by Bitar et al., our patient had no associated intracardiac defects or valvular abnormalities, and the diagnosis was established noninvasively by contrast-enhanced CT. Miraldi et al. [19] described another rare configuration in which the right SVC drained into the LA and the left SVC into the coronary sinus, with a large interjugular bridging vein that allowed partial mixing of venous return and prevented significant desaturation. In contrast, our case lacked such a bridging vein, which likely facilitated more direct left-sided venous drainage and produced a small right-to-left shunt responsible for mild hypoxemia. These comparisons underscore the anatomic and hemodynamic diversity of systemic venous return anomalies and demonstrate how subtle variations in venous connections can markedly influence clinical presentation.

In evaluating abnormalities of the vascular system, including a PLSVC, contrast-enhanced computed tomography (CECT) continues to be the preferred imaging technique owing to its superior image resolution, multiplanar capability, and ability to delineate vascular anatomy and drainage patterns [20,21]. In our case, a double SVC with a left-sided vessel draining into the LA was incidentally identified on CT performed with a PTE protocol. The abnormal vein was visualized adjacent to the aortic arch and traced to its anomalous termination. While echocardiography was used to assess cardiac structure and function, including right heart dilation and pulmonary pressures, it lacked the anatomic detail necessary to characterize the vascular anomaly. This highlights the complementary role of multimodal imaging, with CT offering definitive anatomical diagnosis in clinically silent but potentially significant venous variants.

This case is distinctive because it demonstrates a rare configuration of SVC with direct left SVC drainage to the LA, without concurrent atrial septal defect or unroofed coronary sinus. Such a presentation is exceptionally uncommon and differs from previously described variants such as Raghib syndrome or cases with coronary sinus connection. In contrast to most reports where diagnosis was established incidentally during cardiac surgery or invasive procedures, in our patient the anomaly was identified noninvasively through contrast-enhanced CT performed for pulmonary evaluation.

Clinically, the recognition of this anomaly is important because inadvertent left-sided central venous access or pacemaker placement could lead to systemic embolization or paradoxical events due to the right-to-left shunt. Awareness of this pattern may prevent potential complications during interventional or anesthetic procedures. Therefore, this case not only adds to the spectrum of LSVC anomalies but also underscores the value of cross-sectional imaging in identifying rare venous variants that have meaningful procedural and diagnostic implications.

Conclusion

PLSVC emptying to the LA is an uncommon vascular anomaly that can lead to right-to-left shunt and potential systemic hypoxemia. However, as demonstrated in this case, such anomalies may remain clinically silent and are often identified incidentally during imaging for unrelated conditions. The absence of overt hypoxemia in our patient, despite abnormal venous drainage, may be attributed to long-term physiological adaptation from chronic smoking. This case underscores the importance of recognizing vascular variants during imaging interpretation, as their presence may have implications for diagnostic procedures, interventional planning, and long-term management.

Declaration of generative AI and AI-assisted technologies in the manuscript preparation process

During the preparation of this work, the author(s) used ChatGPT by OpenAI for grammar checking, language editing, and text enhancement. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article.

Patient consent

Informed consent was duly obtained from the patient for the use of clinical information and imaging data, including for the purposes of publication.