In this instance the traumatic history was minor and the radiological interpretation was that this abnormality simply reflected a normal variation of a cervical aortic arch, with both the ascending and descending board crisply visualised. There are no features of rib notching to suggest recurrent lesion associated with a prominent ascending aorta/arch. However, the clinical team was less confident, therefore, insisted on CT.
The CT images were performed following injection of contrast from the left arm. The top left image demonstrates the aortic arch is indeed cervical, appearing at the level above the clavicles. On this image the left axillary and brachiocephalic vein can be seen densely opacified with contrast. The second image (top right) demonstrates two abnormalities. Firstly the most anterior venous structure in the thorax, namely the left brachiocephalic vein is absent, hence the ascending aorta is in contact with the sternum. In addition there is a dense contrast opacified structure lying lateral to the trachea, passing posterior to the aorta on this image reflecting the congenitally displaced left brachiocephalic vein passing posterior to the ascending aorta. On the final image this passes anterior to the trachea and joint the right brachiocephalic vein to form a conventional SVC. There is no shunt.
This congenital variation is named cervical aortic arch with subaortic brachiocephalic vein. It is a rare benign variation that may become apparent during catheter insertions. It is also important to recognise on non contrast imaging as a potential confusing appearance. The unipacified vessel posterior to the aorta on non contrast imaging can be confused as the right pulmonary artery and in the right paratracheal space for a lymph node. The absence of a brachiocephalic vein at surgery may be confused for a duplicated left SVC which this is not.
The presence of a vertically oriented vessels in the left prevascular space has a limited differential. In addition to subaortic brachiocepahlic vein this may include partial or total anomalous pulmonary venous return or left sided superior vena cava. The cause of this particular congenital abnormality is uncertain but likely relates to abnormality development of the middle cardinal vein. You will recall that persistence of the cardinal vein is associated with a left-sided SVC which would descend further down the left side of the cardiac silhouette , via the ligament of Marshall (in the left wall of the left atrium) into the coronary sinus. It has been stated and the incidence of left-sided SVC is less in patients with left brachiocephalic subaortic veins, alluding to different insults of the cardinal vein embryogenesis, however, as this abnormality is so rare such associations are difficult to assess. In and of itself this abnormality is asymptomatic and not usually asssociated with other cardiac disease or significant abnormalities.