Introduction

The right superior vena cava (RSVC) draining into the left atrium is a rare malformation causing cyanosis and clubbing in patients in whom no other signs of congenital heart defects are present. Patients are generally slightly symptomatic with mild cyanosis [1]. The diagnosis is usually made by cardiac catheterization. We report an extremely rare case of anomalous systemic venous return with the RSVC draining into the left atrium evaluated using multidetector CT.

Case report

A 13-month-old boy, with no family history of congenital heart disease, came to our attention because of mild systemic cyanosis reported by his paediatrician during a routine well-child visit. On physical examination no cardiac murmur was found, femoral pulses were normal, and there were no signs of chronic heart failure or syndromic dysmorphism; peripheral oxygen saturation was 94%. ECG showed sinus rhythm and no evidence of atrioventricular arrhythmia.

Transthoracic echocardiography showed situs solitus, levocardia with atrioventricular and ventriculoarterial concordance, normal-size ventricles and an atrial septal defect that was haemodynamically not significant. The hepatic segment of the inferior vena cava was present and drained normally into the right atrium. The superior vena cava was correctly detected but its drainage was not clearly identified. The pulmonary vein drainage was apparently into the left atrium. The absence of other features to explain cyanosis led to the presumptive diagnosis of anomalous drainage of the RSVC into the left atrium or pulmonary arteriovenous malformation.

We performed a cardiac CT scan (LightSpeed VCT, General Electric, Milwaukee, WI) to definitively assess the diagnosis. The parameters were as follows: rotation time 0.4 s, pitch 0.984, beam collimation 64×0.625 mm, 80 kVp, mA modulated during acquisition, peripheral injection of contrast agent (Iohexol 300 mgI/ml, volume 1.5 ml/kg, injection rate 0.5 ml/s) followed by 5 ml saline solution. Images were acquired at the end of the injection. The acquisition lasted 1.1 s and the examination lasted approximately 15 min in total. A very unusual variety of systemic venous return was found (Fig. 1), confirming anomalous drainage of the RSVC into the left atrium without any other intracardiac defect. There were two large pulmonary veins draining the right lung, and two draining the left lung. The four pulmonary veins were normally connected to the left atrium. No left superior vena cava was detected.

Fig. 1
figure 1

Coronal oblique images with maximum intensity projection show the RSVC draining into the left atrium (Ao ascending aorta, LA left atrium, LV left ventricle, RSVC right superior vena cava)

Full size image

Surgery confirmed the diagnosis of RSVC draining into the left atrium. Four large pulmonary veins (two for each lung) were normally connected to the left atrium. Additionally, there were two very small accessory pulmonary veins coming from the right middle lung and draining into the RSVC at its junction with the left atrium. Surgical correction was performed, consisting of transection of the RSVC just above the two accessory pulmonary veins following by end-to-end anastomosis of the RSVC with the right atrial appendage.

Discussion

A persistent left superior vena cava draining into the right atrium via the coronary sinus is a well-known systemic thoracic venous anomaly, generally associated with other cardiac malformations such as an atrial septal defect [2]. Isolated anomalous drainage of the RSVC into the left atrium is much less common. The right-to-left shunt causes mild cyanosis and patients are generally free of symptoms, explaining the delay in diagnosis. This anomaly should be considered in the differential diagnosis of intracardiac right-to-left shunt, pulmonary arteriovenous malformation, methaemoglobinaemia, and classic causes of hypoxaemia such as lung disease or chronic pulmonary embolism. In adulthood, symptoms are neither evident nor specific, with digital clubbing, shortness of breath and poor physical development. Although rare, more severe complications may be encountered, including congestive heart failure, paradoxical embolism and brain abscesses [3].

Complete diagnosis of both the RSVC draining into the left atrium and the partial anomalous pulmonary venous drainage may be challenging. Our observation points to this constant association; the partial anomalous pulmonary veins are always present, as confirmed at surgery in our patient. The embryology of this rare anomaly is discussed by Van Praagh et al. [1]. Of the 41 cases they reviewed, biatrial or left atrial drainage of the RSVC was always associated with anomalous pulmonary venous drainage. Indeed, the mechanism for this anomaly is not true anomalous drainage of the RSVC, but rather a deficiency of the common wall between the RSVC and pulmonary veins.

Echocardiography with colour flow mapping is the standard initial screening modality. However, it may be insufficient or inaccurate, especially when there is a poor acoustic window. Although invasive with attendant risks, cardiac catheterization is the standard reference in this setting, providing comprehensive information about the drainage of systemic veins with haemodynamic details. CT is an interesting alternative technique that provides high-precision multiplanar and three-dimensional imaging, particularly useful for diagnostic work-up of complex forms of congenital heart disease [4]. CT was chosen in our patient as our differential diagnosis was pulmonary arteriovenous malformation, which is well seen by CT. However, the price to pay is the use of iodine contrast agent and the ionizing radiation that must be taken into account in the risk/benefit assessment. It is important to apply the ALARA principle [5] and systematically adapt parameters to the weight of the infant to limit the absorbed dose. MRI is another less-invasive alternative in this setting, and avoids ionizing radiation. However, it is still limited in daily practice in the paediatric population because of the complexity of the protocols, the long scanning time, and the need for sedation or general anaesthesia in small children [6].

In summary, anomalous drainage of a systemic vein should always be considered in a child with cyanosis. Left atrial drainage of the RSVC is always associated with anomalous pulmonary venous drainage, as the mechanism for this anomaly is a deficiency in the common wall between the RSVC and pulmonary veins.