Clinical Significance and Imaging Findings of Left Superior Vena Cava Draining into Right Superior Vena Cava

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1. Introduction

The left superior vena cava (LSVC) is among the most common thoracic venous anomalies, reported in approximately 0.3–0.5% of the general population. Normally, the right superior vena cava (RSVC) serves as the principal venous channel, directing deoxygenated blood from the head and upper extremities into the right atrium. However, due to embryologic variations, a persistent left-sided superior vena cava may remain.

In most cases, the LSVC drains into the coronary sinus, typically without clinical consequences. In some patients, however, anomalous drainage into the left atrium or, as in this case, into the right superior vena cava may occur. Such variations, if unrecognized, may lead to complications during cardiac catheterization, central venous line placement, cardiac surgery, or pacemaker lead insertion.

This case demonstrates a rare anomaly in which the LSVC courses inferior to the aortic arch and drains directly into the RSVC — a highly unusual pattern scarcely reported in the literature. This review summarizes the pathophysiology, epidemiology, clinical presentation, imaging findings, differential diagnosis, treatment, and prognosis of this anomaly.

2. Pathophysiology

The development of an LSVC results from aberrations in embryonic venous maturation. During normal embryogenesis, venous return from the upper body derives from paired anterior cardinal veins.

By the 8th week of gestation, the left anterior cardinal vein normally regresses, leaving only the left brachiocephalic vein, while the right anterior cardinal vein persists to form the RSVC. Failure of regression of the left anterior cardinal vein leads to persistence of an LSVC.

Typically, the LSVC drains into the coronary sinus and ultimately into the right atrium, causing minimal hemodynamic consequences. However, variant connections may have clinical implications.

In this case, the LSVC drains directly into the RSVC, leading to several notable pathophysiological features:

  1. Collateral venous pathway

    • Venous return from the left upper extremity and head crosses inferior to the aortic arch to join the RSVC.

    • This abnormal trajectory can be identified radiographically as a venous structure coursing beneath the aortic arch.

  2. Absence of coronary sinus dilatation

    • LSVC draining into the coronary sinus usually results in sinus dilatation.

    • In RSVC-draining variants, the coronary sinus remains normal in caliber.

    • Thus, the coexistence of a normal-sized coronary sinus with an LSVC is a key diagnostic clue.

  3. Risk of procedural complications

    • When inserting central venous catheters or pacemaker leads from the left side, devices may unexpectedly traverse the LSVC–RSVC route, complicating placement and increasing the risk of malposition.

    • Recognition of this anomaly before intervention is therefore critical.

3. Epidemiology

LSVC is a rare congenital venous anomaly, found in about 0.3–0.5% of the general population, but in 4–10% of patients with congenital heart disease (CHD).

The clinical significance depends on the drainage pattern:

  • Into the coronary sinus: >90% of cases; usually asymptomatic.

  • Into the left atrium: 8–10% of cases; creates a right-to-left shunt with risks of hypoxemia and systemic embolism.

  • Into the RSVC: extremely rare; only a handful of cases documented.

👉 The present case therefore represents a <0.1% occurrence in the general population.

No significant sex predilection exists, and most cases are discovered incidentally during CT or MRI.

4. Clinical Presentation

Most LSVC anomalies are asymptomatic and detected incidentally. The clinical impact depends on the drainage site and associated anomalies.

  1. Incidental detection

    • The most common scenario.

    • In this case, a 51-year-old male underwent CT to rule out occult malignancy; the LSVC anomaly was incidentally discovered without symptoms.

  2. Complications during central venous access

    • Catheters inserted via the left side may follow the LSVC–RSVC course beneath the aortic arch, causing malposition.

    • This also complicates procedures such as pacemaker implantation and cardiopulmonary bypass cannulation.

  3. Electrophysiological implications

    • LSVC draining into the coronary sinus may cause coronary sinus dilatation and predispose to atrial fibrillation or conduction disturbances.

    • In contrast, RSVC-draining LSVC (as in this case) does not enlarge the coronary sinus and carries a lower arrhythmogenic risk.

  4. Association with congenital heart disease

    • LSVC is more common in patients with ASD, VSD, or Tetralogy of Fallot.

    • It may rarely exist in isolation, as in this patient.

  5. Symptomatic presentations

    • LSVC draining into the left atrium can cause cyanosis, hypoxemia, or paradoxical embolism.

    • RSVC drainage, however, typically remains asymptomatic.

✅ Summary:
An LSVC draining into the RSVC is usually asymptomatic but must be recognized to prevent procedural complications.

5. Imaging Features

LSVC anomalies are most often detected incidentally on imaging, particularly contrast-enhanced CT, cardiac MRI, or echocardiography.

In this case, arterial-phase contrast-enhanced CT demonstrated the following key findings:

[Figure 1] Axial contrast-enhanced CT, arterial phase

📌 Interpretation:

  • The LSVC is seen coursing inferior to the aortic arch.

  • It begins to angle toward the right, approaching the RSVC.

[Figure 2] Axial contrast-enhanced CT, arterial phase

📌 Interpretation:

  • The LSVC continues toward the RSVC, visualized on this axial slice.

  • No coronary sinus dilatation is noted, confirming drainage into the RSVC rather than the coronary sinus.

[Figure 3] Coronal contrast-enhanced CT, arterial phase

📌 Interpretation:

  • The course of the LSVC crossing beneath the aortic arch is clearly delineated.

  • Venous return from the left upper body converges into the RSVC.

  • A small left brachiocephalic vein draining into the RSVC is also visible.

[Figure 4] Sagittal contrast-enhanced CT, arterial phase

📌 Interpretation:

  • The connection between the LSVC and RSVC is well visualized in sagittal view.

  • The abnormal left-to-right venous trajectory is apparent.

Summary of Imaging Findings

  1. LSVC coursing inferior to the aortic arch → hallmark feature of this rare variant.

  2. No coronary sinus dilatation → consistent with RSVC rather than coronary sinus drainage.

  3. Small left brachiocephalic vein draining into RSVC as an additional anomaly.

  4. Multiplanar CT imaging (axial, coronal, sagittal) demonstrates the LSVC–RSVC continuity unequivocally.

👉 These findings confirm a rare venous anomaly: an LSVC draining into the RSVC beneath the aortic arch.

6. Differential Diagnosis

Although rare, LSVC anomalies must be distinguished from other mediastinal structures or pathologies:

  1. Duplicated Superior Vena Cava

    • Both LSVC and RSVC coexist independently, often connected by a bridging vein.

    • Unlike this case, they do not merge directly.

  2. Anomalous vein or venous varix

    • Mediastinal venous dilatations may mimic LSVC.

    • However, their course is irregular and drainage patterns differ.

    • Multiplanar reconstruction helps confirm LSVC’s characteristic path under the aortic arch.

  3. Aortic arch lymphadenopathy

    • Enlarged lymph nodes or metastatic disease beneath the arch can simulate an LSVC.

    • Nodes lack venous continuity and show different contrast enhancement patterns.

  4. Arteriovenous malformation (AVM)

    • Complex vascular malformations may be misinterpreted as LSVC.

    • AVMs demonstrate simultaneous arterial and venous filling, unlike LSVC.

  5. Coronary sinus dilatation

    • Seen when LSVC drains into the coronary sinus.

    • Absence of coronary sinus enlargement in this case helps exclude this variant.

Key diagnostic approach:

  • Assess multiplanar continuity of the vessel.

  • Evaluate contrast enhancement pattern.

  • Confirm drainage site.

7. Treatment

Most LSVC anomalies, especially RSVC-draining types, require no treatment.

1) No treatment required (RSVC drainage, asymptomatic)

  • Venous return is physiologically directed to the right atrium.

  • No hemodynamic compromise.

  • Management: observation and procedural awareness (e.g., during central venous access or cardiac interventions).

2) Treatment required (Left atrial drainage, symptomatic)

  • Causes right-to-left shunt with hypoxemia, cyanosis, or paradoxical embolism.

  • Options include:

    • Surgical repair: ligation or reimplantation into RSVC/right atrium, often during open-heart surgery.

    • Endovascular occlusion: catheter-based closure with coils or devices, particularly in embolic risk.

3) Procedural considerations

  • Central venous catheterization: Left-sided catheters may traverse unexpected LSVC–RSVC route.

  • Pacemaker/ICD lead placement: Technically more challenging due to anomalous trajectory.

  • Cardiac surgery: Must be identified preoperatively to avoid errors in cannulation and venous return management.

👉 In summary, management is primarily recognition and precaution, with intervention reserved for cases of left atrial drainage.

8. Prognosis

The prognosis depends on the drainage site and associated anomalies:

  1. RSVC drainage (this case)

  • Hemodynamically benign.

  • Lifelong asymptomatic course.

  • Excellent prognosis.

  1. Coronary sinus drainage

  • Most common variant.

  • May predispose to arrhythmias due to coronary sinus dilatation, but generally benign.

  1. Left atrial drainage

  • Clinically significant due to right-to-left shunt.

  • Risk of hypoxemia, stroke, systemic embolism.

  • Untreated: poor prognosis.

  • With surgical/interventional correction: good outcome.

  1. Associated congenital heart disease

  • Prognosis depends on the underlying cardiac defect (ASD, VSD, TOF, etc.).

Summary:
An LSVC draining into the RSVC is among the safest variants with an excellent prognosis.

Quiz

Q1. Which of the following is true regarding the left superior vena cava (LSVC)?
A. Occurs in 5–10% of the general population
B. Most commonly drains into the coronary sinus
C. Left atrial drainage is the most common variant
D. RSVC drainage is the most common variant
E. Always symptomatic

✅ Answer: B
Explanation: LSVC occurs in 0.3–0.5% of the population (higher in CHD). >90% drain into the coronary sinus. Left atrial drainage is <10%. RSVC drainage is extremely rare. Most are asymptomatic.

Q2. Major clinical concern in LSVC draining into the left atrium?
A. Arrhythmia
B. Hypoxemia and risk of embolism
C. Upper extremity edema
D. Pulmonary hypertension
E. Superior vena cava syndrome

✅ Answer: B
Explanation: Left atrial drainage produces a right-to-left shunt, leading to hypoxemia, cyanosis, and paradoxical embolism.

Q3. Key diagnostic clue for LSVC on imaging?
A. Inhomogeneous enhancement after contrast
B. Mass-like appearance near the aortic arch
C. Demonstration of continuous venous pathway on multiplanar imaging
D. Simultaneous arterial and venous filling
E. Coronary sinus dilatation alone

✅ Answer: C
Explanation: Continuity of venous course on multiplanar CT/MRI is the most reliable diagnostic feature.

References

[1] G. Goyal, R. B. Punnam, S. Verma, and M. Ruberg, “Persistent left superior vena cava: a case report and review of literature,” Cardiology Research and Practice, vol. 2010, pp. 1–5, 2010.

[2] M. Povoski, L. Khabiri, and J. Marsh, “Persistent left superior vena cava: review of the literature, clinical implications, and relevance of alterations in thoracic central venous anatomy as pertaining to the general principles of central venous access device placement and venography,” World Journal of Surgical Oncology, vol. 17, no. 1, pp. 1–12, 2019.

[3] H. Buirski and J. R. Jordan, “Left superior vena cava draining into the left atrium,” British Heart Journal, vol. 43, no. 5, pp. 590–593, 1980.

[4] Y. Sarodia and A. Stoller, “Persistent left superior vena cava: case report and literature review,” Respiration, vol. 69, no. 3, pp. 287–290, 2002.

[5] C. G. Irwin, H. T. Grech, and J. F. Keeley, “Anomalous systemic venous return,” Circulation, vol. 117, no. 11, pp. 159–163, 2008.

[6] S. Goyal, M. Rosenthal, and R. J. Williams, “Congenital anomalies of the thoracic systemic veins,” AJR American Journal of Roentgenology, vol. 210, no. 5, pp. 1171–1181, 2018.

[7] E. P. Dillman, B. J. Yarrarapu, and C. R. Villines, “Persistent left superior vena cava: diagnosis, significance, and clinical implications,” Radiology Case Reports, vol. 12, no. 1, pp. 47–50, 2017.

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