A rare case of persistent left superior vena cava

A 44-year-old female patient with pain and redness of both eyes and mild frontal headache presented with eye Outpatient department. Ophthalmoscopic examination revealed a salmon patch in the left eye. Secondary lymphoma of both eyes was clinically suspected. A routine blood picture showed microcytic normochromic anaemia.

Contrast-Enhanced Computed Tomography (CECT) of chest showed an accessory contrast-filled vessel in the left visceral mediastinum extending from the thoracic inlet to the right atrium. It originates from the confluence of the left subclavian vein laterally and the left internal jugular vein superomedial, separate from the left common carotid artery and left subclavian artery (figure 1a). Figures 1b and 1c show a vessel running in the left prevascular space anterolateral to the arch of the aorta and draining into coronary sinus. Right-sided superior vena cava appears smaller. In addition,coronary sinus appears mildly dilated, commonly a sign of persistent left superior vena cava. Figure 2a shows vessel running laterally to the arch of the aorta and left main pulmonary artery. Figure 2b shows vessel joining the coronary sinus, terminating in right atrium. Figure 3 shows the arch of the aorta, causing mild posterior indentation of the vessel.

Superior vena cava (SVC) duplication is most common form of a left-sided SVC, where standard right-sided SVC remains. Therefore, When variable course of catheter or wire is noted in left prevascular /visceral mediastinum in chest X-ray, persistence of left SVC should be suspected. This variant occurs in 0.3% to 0.5% of general population and up to 4.5% of patients with other associated cardiac anomalies [1,2]. Lin et al. [3] demonstrated that SVC is often irregular in shape on cross-sectional images. They have suggested a normal range for the major axis (1.5–2.8 cm) and minor axis (1–2.4 cm).

Three paired cardinal veins drain the embryo's body at 5th week, cephalic portion is drained by paired anterior cardinal vein, and  caudal part is drained by paired posterior cardinal vein. Usually positioned right-sided SVC is formed by proximal right anterior cardinal vein, right common cardinal vein and right horn of sinus venosus. Posterior cardinal vein forms part of azygos vein.

Part of left anterior cardinal vein forms left superior intercostal vein and adjacent left brachiocephalic vein[1].

Raghib syndrome/unroofed coronary sinus is when persistent left SVC opens into left atrium with absent coronary sinus, creating a right-to-left shunt. In symptomatic patients with stroke, brain abscess and systemic embolisation ligation of left SVC can be performed with an adequately sized bridging vein. In addition, persistent left SVC may generate difficulty placement of pacemakers, implantable cardioverter-defibrillator leads, and Swan-Ganz catheters[4,5].

Persistent left SVC is a relative contraindication to performance of retrograde cardioplegia during coronary artery bypass grafting [6].

Contrast-enhanced Computed Tomography is the investigation of choice that detects vessel's origin, course and drainage. Dedicated contrast-enhanced CT protocols include a 60–75 seconds delay after injection. Furthermore, during CT angiography, window level,100 HU; window width,600-700 HU, and diluted contrast material can minimise streak artefacts. In addition, to detect an SVC thrombus and to minimise mixing artefacts, additional delayed acquisition at 60 seconds is often valuable [7].

Magnetic Resonance Imaging (MRI) can be reserved as a problem-solving modality.

Teaching point

Appropriate knowledge of appearance of SVC variants and their drainage before any central vascular intervention or catheterisation can minimise significant vascular complications or bleeding risks.

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