Teaching Case

A 64-year-old female presented with acute hypoxic respiratory failure requiring intubation. A CT pulmonary angiogram (CTPA) was performed to rule out pulmonary embolism.

CTPA showed no evidence of pulmonary embolism. Rather, axial CT images with contrast (Figure 1) demonstrated an anomalous course of the left brachiocephalic vein. The vein enters the aortopulmonary window posterior to the ascending aorta and above the pulmonary artery. Coronal CT images with contrast (Figure 2) further characterized the tortuous course of the left brachiocephalic vein as it merges into the superior vena cava.

Background

A suboaortic left brachiocephalic vein (SLBV) is a rare anatomic variant present in 0.2-1.7% of patients with congenital heart disease (CHD) [1]. Tetralogy of fallot (TOF) is the most common coexistant CHD, seen in 41.7-88.1% of patients with SLBV [1,2]. Other associations include ventricular septal defect, double outlet right ventricle, and right atrial isomerism. Right-sided aortic arch (RAA) is observed in 62-77.8% of SLBV patients [1,2] and often accompanies TOF [2]. Pulmonary obstruction, whether it be pulmonary atresia or stenosis, can be present in up to 94.4% of patients with SLBV [1].

Clinical and Imaging Perspective

During fetal development, superior and inferior capillary channels anastomose the bilateral anterior cardinal veins, with the superior channel normally becoming the left brachiocephalic vein. In patients with certain arch variants (i.e., RAA or high aortic arch), the superior capillary channel becomes compressed and hindered in growth. Simultaneous deformity of the pulmonary artery (as in atresia or stenosis) leaves vacant the subaortic space, promoting development of the inferior capillary channel and thus an anomalous SLBV [1,2].

The above theory may explain cases of SLBV with congenital malformation. However, isolated cases of SLBV, without CHD and/or vascular aberrations, remain obscure and are exceedingly rare. Only some reports have described isolated SLBV [3-10], which has an incidence of around 0.02% [5]. Radiologically, SLBV must be differentiated from enlarged lymph nodes, persistent left superior vena cava (SVC), central pulmonary artery, elevated right pulmonary artery, and a left vertical vein in total anomalous pulmonary venous return [2-4]. Diligent tracking of the vein on CT is critical for differentiation. The use of IV contrast may aid in visualization.  

Outcome

The tortuous route of SLBV portends difficulty in transvenous pacemaker insertion and central venous catheterization through a left approach [2]. For cardiologists that employ transradial cardiac catheterization, awareness of SLBV can alter procedural methodology. During median sternotomy, surgeons may erroneously believe that the left brachiocephalic vein is absent [3,8]. Without prior knowledge of SLBV, accidental injury to the vessel can occur during cardiac surgery [2]. Additionally, when performing cardiopulmonary bypass, SVC cannulation must be done carefully to avoid obstruction of the SLBV, as it enters the SVC more caudally than normal [2,3].

Take Home Message

The paucity of literature on isolated SLBV, without other malformations, warrants familiarity of this anomaly. CT is most practical for diagnosis, but this anomaly can also be seen on MRI. Prompt recognition by the radiologist is crucial, as SLBV has procedural and surgical implications.  

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