Incidental but indispensable finding: Persistent left superior vena cava

A 73-year-old female with chronic cough was admitted to our hospital with complaints of breathlessness for 1 week. The jugular venous pressure was elevated, bilateral pitting pedal oedema was present, and a long systolic murmur was heard in the tricuspid area. A 2D echocardiogram showed dilated right atrium (RA) and right ventricle (RV), severe tricuspid regurgitation/pulmonary arterial hypertension (TR/PAH), and RV dysfunction. ECG showed a right bundle branch block. The patient was referred to our department for a CT pulmonary angiogram.

CT pulmonary angiogram showed a thrombus in the right pulmonary artery (Figure 1) and its branches, and a focal thrombi in the left descending pulmonary artery and its branches.

Incidentally, we noted variant anatomy in the venous system of the thorax. The right brachiocephalic vein, formed by the union of the right internal jugular vein and right subclavian vein, was seen continuing as superior vena cava. The left brachiocephalic vein was absent (Figure 2). A persistent left superior vena cava (Figures 3, 4, 5 and 6) was noted draining into the right atrium through the coronary sinus (Figures 3 and 4). Features of right heart failure were noted: right atrium and right ventricle were dilated, and there was reflux of contrast into dilated intrahepatic inferior vena cava and hepatic veins.

Background and Imaging Perspective

Persistent left superior vena cava (PLSVC) is a rare but most common anomaly of the venous system of the thorax. Prevalence in general population varies from 0.2 to 3%. In congenital heart disease patients, the prevalence varies from 1.3 to 11% [1].

SVC develops from the cardinal system of veins, which is one of the three primitive venous systems, along with the umbilical and vitelline systems. There are symmetrical (right and left) pairs of anterior and posterior cardinal veins. Anterior cardinal veins drain the cranial aspect, and posterior cardinal veins drain the caudal aspect of the embryo. These join to form the right and left common cardinal veins, which drain into the ipsilateral horns of the sinus venosus and then to the heart (Figure 7). SVC (Figure 8) develops by forming bridging anastomosis between the right and left anterior cardinal veins. Bridging anastomosis develops into the left brachiocephalic vein (BCV). Then, there is an obliteration of the caudal part of the left anterior cardinal vein, forming the ligament of Marshall. The left sinus venosus and left common cardinal vein form the coronary sinus. The proximal right anterior, right common cardinal vein and right sinus venosus form the normal SVC.

Failure of regression of the left anterior cardinal vein and adjacent part of the left common cardinal vein results in PLSVC (Figure 9). Various hypotheses have been postulated regarding the development of PLSVC. One of these is the “low left atrial pressure theory”, which states that low pressure in the left atrium, due to other anomalies, fails to compress the coronary sinus and left cardinal vein, leading to the formation of PLSVC [1,2].

In 90% of cases, PLSVC is associated with a normal SVC on the right, known as double SVC (DSVC). If SVC does not develop on the right in the presence of a PLSVC, it is called isolated PLSVC (IPLSVC) and is associated with cardiac anomalies and cardiac situs disorders. Single ventricle, atrial and ventricular septal defects, tetralogy of Fallot have been reported as most common associated cardiac anomalies [3–5]. Other associations include the right-sided arcus aorta, coarctation of the aorta, and heterotaxy [6].

Clinical Perspective

Although PLSVC is asymptomatic and detected incidentally, there is some clinical significance. Dilated coronary sinus associated with PLSVC can compress the atrioventricular node and the bundle of His and cause arrhythmias. It can complicate mitral valve surgery [7]. PLSVC detection is important before invasive procedures like central venous catheter insertion, cardiac resynchronisation therapy or pacemaker implantation [1,2]. Detection of PLSVC is also important before some cardiac surgeries like venous rerouting procedures, surgeries with cavo-pulmonary anastomosis and transplantation surgeries [1].

Teaching Points

PLSVC is usually insignificant and asymptomatic, but it can cause significant problems in a few clinical scenarios. Therefore, its detection is important and should be reported in radiology reports even if detected incidentally.