Acquired Systemic-to-pulmonary Venous Shunt or Persistent Left Superior Vena Cava? A Rare Right-to-left Shunt Case-based Discussion.

Cardiac shunts are often described in congenital or pediatric populations, but systemic-to-pulmonary venous shunts in adult patients are reported in literature in isolated case reports. We present the case of a 70-year-old female with a left superior vena cava (SVC) draining into the left atrium by the left superior pulmonary vein, with a complete right-to-left shunt of the superior venous circulation caused by a former catheter thrombosis in the right SVC. Diagnosis was suspected after a contrast echocardiography showing an exclusive perfusion of left heart after intravenous injection and confirmed by helical computed tomography with three-dimensional reconstruction. After medico-surgical discussion, a first-line conservative treatment with oxygen therapy was chosen, due to the stability of symptoms and high predicted risk of perioperative mortality. The particularities of this case are that we cannot determine if the origin of this shunt is a latent persistent left SVC becoming symptomatic after the SVC obstruction or an abnormal collateral pathway due to the thrombosis and the unusual indirect communication through a pulmonary vein.

INTRODUCTION

Diagnostic approaches of cardiac shunts do not belong to only pediatric populations. Cases of acquired cardiac shunts could rise in adult patients, with growing incidence of cancers and wider use of central venous access devices.

CASE REPORT

A 70-year-old female had been complaining of chronic dyspnea for a few years. Her past medical history was colorectal cancer treated 12 years ago by surgery and adjuvant chemotherapy and considered in total remission. A central venous catheter thrombosis in superior vena cava (SVC) had required the device's ablation at the same time. She described exertional dyspnea, without other symptoms. On physical examination, the patient presented cyanotic extremities with low oxygen saturation of 90% in room air, normal blood pressure, and heart rate. The chest radiography and pulmonary function testing showed no abnormalities. Hemoglobin and hematocrit levels were 16 g/dL and 48%, respectively. Arterial blood gas showed hypoxemia with mean PaO2 65 mmHg.

After normal chest radiography, transthoracic echocardiography [Figure 1] showed a normal left ventricular systolic function, no valvular disease, and normal size cavities. Systolic pulmonary arterial pressure was below 35 mmHg, estimated on a trivial tricuspid regurgitation. No septal defect was detected. A contrast echocardiography was performed with saline injection through the right antecubital vein and suggested a right-to-left shunt because of immediate and exclusive perfusion of the left cavities. The adjuvant transesophageal echocardiography confirmed the absence of patent foramen ovale/atrial septal defect or any other cardiac congenital anomalies and showed no Doppler flow at the opening of the occluded SVC. A chest computed tomography (CT) angiography was performed with three-dimensional (3D) reconstruction; images were acquired in helical mode using multidetector CT scan and diagnosed a left SVC draining into the left atrium by an unusual indirect communication through a left superior pulmonary vein [Figures 2 and 3], with occluded “right” SVC since the catheter thrombosis. Coronary sinus was not dilated. A large part of superior venous system (1/3 of total venous return) is directly draining into the left heart, but relatively good tolerance with minimal hypoxemia could be indicative of other hypothetic collateral pathways that were not pointed out by the imaging study. About therapeutic options, first-line conservative treatment with oxygen therapy was decided instead of heavy vascular surgery after “heart team” discussion, due to the stability of symptoms and the high predicted risk of perioperative mortality.

Figure 1

Contrast transthoracic echocardiography with exclusive perfusion of left cavities after a venous injection suggesting the shunt

Figure 2

Three-dimensional reconstruction of helical computed tomography showing a left superior vena cava draining into a left superior pulmonary vein (A) with occluded former “right” superior vena cava (B)

Figure 3

Detailed image of left superior vena cava-left atrium connection through the left superior pulmonary vein

DISCUSSION

Superior venous system is draining into the left heart, realizing an extremely rare case of systemic-to-pulmonary venous shunt, but we cannot determine if the origin of this shunt is a persistent left SVC as a latent congenital anomaly becoming symptomatic after the SVC obstruction or an abnormal collateral pathway due to the thrombosis. Morphological normality of the coronary sinus and good tolerance could be some clues to consider that the left SVC as one of the pathways appeared after the thrombosis.

“Systemic-to-pulmonary venous shunts can be formed by three different mechanisms: anatomic, congenital, or acquired. In the anatomic type, bronchial veins and pulmonary veins are connected through bronchial venous plexuses. These plexuses are located in the bronchial wall and peribronchovascular connective tissue. In physiological conditions, the pleurohilar bronchial veins communicate with the azygos and hemiazygos venous system with valves preventing backflow. A right-to-left shunt with reversed flow can be observed after elevated pressures with valve insufficiency. In the congenital type of shunt, three shunting pathways are described: an aberrant pulmonary venous return with reversed flow, a levoatriocardinal embryologic remnant, and a persistent left SVC. Concerning acquired systemic-to-pulmonary venous shunts described by Liebow[1] in 1953, SVC obstruction might be caused by different etiologies, such as malignant diseases in 85% of cases or benign processes such as central venous catheter or mediastinal fibrosis. The mechanism is not well known, inflammation and adhesion of the pleura are considered to be essential for angiogenesis of bridging veins penetrating across the pleura. Collateral pathways are formed mainly by the azygos, the internal/external mammary, lateral thoracic, or vertebral veins to maintain venous drainage from the upper extremities.”[2] Rare cases of abnormal venous return after SVC obstruction are described in literature, realizing a systemic-to-pulmonary venous shunt when draining directly into the left side of the heart.

Diagnosis and understanding of these rare cases have been developed by radiology. The place of echocardiography with contrast, specifying the site of injection is described,[3] to grading the shunt and search intracardiac right-to-left shunts, as patent foramen ovale. Conventional or helical CT angiography with 3D reconstruction is reported in literature as important diagnostic tools.[2] Other methods are described for depicting these rare cases. CT venography[2] could be useful because it can show the cause of SVC syndrome and its exact level and the collateral pathways. Perfusion lung scan using 99mTc-aggregated albumin shows an unusual accumulation with a trapping of tracer in collaterals as a direct sign of obstruction.[4] Radionuclide venogram can also show the obstructed vessel.[5]

CONCLUSIONS

This case leaves open the question “Is this shunt the result of an acquired collateral pathway draining into the left heart or an ignored persistent left SVC becoming really symptomatic after the loss of thrombotic SVC?” That kind of indirect communication through pulmonary vein is also extremely rare. Finally, the presence of other hypothetic collateral pathways could explain the relatively good tolerance with mild clinical manifestations. Diagnosis of systemic-to-pulmonary venous shunt means a pluridisciplinar approach. Intracardiac and congenital right-to-left shunts with their management are well described in literature. Regarding the few cases reported, imaging seems to be the key for diagnostic. Therapeutic options have to be discussed on a case-by-case basis.

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Conflicts of interest

There are no conflicts of interest.