Teaching Case

A 60-year-old apyretic man presents with dyspnea and increased D-Dimeres levels on blood tests. He underwent an angio-CT.

No pulmonary embolism was found. However, the angio CT displayed on mediastinal view an aberrant vessel left to the aortic arch which drains into the right atrium, corresponding to an aberrant left superior vena cava. The right superior vena cava was absent. No other associated vascular abnormalities were found.

Background

Persistent superior vena cava (PLSVC) is rare as it is seen in only 0.3 to 0.5% of the population. Yet, it is the most common thoracic veinous abnormality.

The primitive veinous system consists of the cardinal veins, umbilical veins and vitelline veins. PLSVC is seen when the left superior cardinal vein and its continuity with the left common cardinal vein fail to regress. The presence of a left superior vena cava along with a right superior vena cava is much more frequent, and the condition is called the double superior vena cava. Isolated PLSVC without a right vena cava is very rare.

Right atrial drainage is the most frequent and is associated with a large coronary sinus. Left atrial drainage causes a left to right shunt but it was however sometimes reported without cardiac defects.

Clinical perspective

The clinical relevance of this entity depends on its drainage and cardiac-associated abnormalities. When asymptomatic, it is discovered incidentally on chest examinations. In most cases, the PLSVC drains into the right atrium and the patients are asymptomatic. But in 10-20% of cases, it can drain into the left atrium, causing a right to left shunt, leading to clinical symptoms such as cardiac arrhythmia, chest discomfort, palpitation, and cyanosis.

Imaging

On plain radiographs, LSVC can be detected as a vertical left upper mediastinal vertical limit superimposed to the aortic arch. Sometimes, it is not directly seen on plain radiographs and it can be suspected if a central catheter is in an unexpected left para mediastinal situation.

CT with contrast media administration is the modality of choice for the characterization of this anomalous vessel in the left mediastinum. It is suspected in the presence of a dilated coronary sinus on cross-sectional imaging.

Most cases encounter a PLSVC draining into the right atrium through the coronary sinus. The vessel begins its course at the junction of the left subclavian and internal jugular veins, passes through the left side of the mediastinum, at the left of the ductal arch, passes anteriorly to the left hilum, and terminates in most cases in the right atrium via the coronary sinus.

CT on axial plane displays a “four vessels” image instead of a three-vessel image. On an axial slice at the level of the main left bronchus, in the case of PLSVC, two veins are seen anteriorly to the bronchus. In the case of a vertical vein, no vein can be seen next to the anterior wall of the left main stem bronchus.

The sagittal plane can show the “ pipe sign”.

In up to 20% of cases, the drainage is into the left atrium directly, through an unroofed coronary sinus, or into the left superior coronary vein.

In 90% of cases, it is associated with a right superior vena cava, making it a superior vena cava duplication, and in those cases, a bridging vein may be seen (left brachiocephalic vein). Sometimes, the left brachiocephalic vein is absent leaving both superior vena cava not connected. Sometimes, the left superior intercostal vein may form a communication between the PLSVC and the accessory hemiazygos vein, forming a left-sided azygos arch.

If PLSVC is isolated (absence of right superior vena cava in 10% of cases), it is either seen with a normal heart or with congenital heart abnormalities: tetralogy of Fallot, atrioventricular canal defect, mitral atresia, atrial/septal ventral defect, transposition of the great arteries, aortic arch abnormalities, etc. It is also present in 50-70% of heterotaxy syndrome cases.

The incidence of congenital heart disease is increased in the absence of the right superior vena cava.

Outcome

• Dilation of the coronary sinus may cause stretching of the arteriovenous node and bundle of his, causing arrhythmia.
• The patient’s outcome depends on the other malformations associated with this condition.

Teaching points

• A vessel on the left side of the aorta in the mediastinum is not always a PSLVC. The beginning, the course, and the end of this vessel must be carefully evaluated to make the correct diagnosis.
• Radiologists must specify on their report if there is a PLSVC even if the patient is asymptomatic. This information might be useful in the case of placement of a central venous device or an eventual cardiac surgery.

All patient data have been completely anonymised throughout the entire manuscript and related files.