Vascular rings are a group of rare congenital abnormalities in which the great vessels form a complete ring of vascular structure around the trachea and oesophagus. Most are due to the persistence of embryological structures, often in combination with abnormal vascular patterns.
They do not cause cardiovascular symptoms. Their clinical significance and management are entirely related to the compression they cause to the trachea and oesophagus. If they cause no compression, then they do not require treatment.
There are three main types of vascular rings:
1. Double Aortic Arch. Commonest variety, accounting for 40 to 50 per cent of cases. This is caused by persistence of the embryological fourth arch causing a complete ring around the trachea and oesophagus (Figures 22.1 and 22.2). Each arch gives rise to a carotid and subclavian artery, and the descending thoracic aorta usually then adopts a normal course down the leftward side of the vertebral columns. Thus, the right arch has to pass behind the oesophagus (creating the characteristic posterior indentation on barium swallow) to reach the left side. Both arches can be of equal size, but the commonest pattern is for the right arch to be dominant – the left side is typically hypoplastic or even atretic (i.e. a fibrous cord) beyond the subclavian origin. It is very rare (almost unknown) for the left arch to be dominant. The ductal ligament will run into the posterior aspect of the arch, creating a second component to the ring.
2. Right Aortic Arch with Left Ductus. This is the second commonest (25 to 30 per cent) and occurs when the arch is right sided (i.e. passes over the right main bronchus) but reverts back to the left side at the descending aorta, where the ductus ligament inserts into it (Figures 22.3 and 22.4). Although the head and neck vessels can arise normally, the commonest arrangement in a vascular ring (70 per cent of cases) is for anomalous origin of the left subclavian from the posterior arch, which is also the site of insertion of the ductus ligament. The anomalous subclavian usually arises from a short out-pouching called the ‘diverticulum of Kommerell’ that represents the persistence of the posterior remnant of the fourth arch. A left arch with right-sided ductus has been reported but is extremely rare.
3. Left Pulmonary Artery Sling. This is the third commonest type (15 to 20 per cent) and differs from the other rings in two important ways: firstly, in that the sling passes only around the trachea, and secondly, the anomaly is strongly associated with varying degrees of tracheal stenosis, including complete tracheal rings (50 to 67 per cent). The sling is created by the aberrant origin of the left PA from the right PA that runs behind the trachea to reach the left hilum (Figure 22.5). The ring is completed by the duct ligament that inserts into the left PA on leftward side of the trachea.
Figure 22.1 Angiogram showing complete double arch. A subclavian and carotid artery arise from each arch.
Figure 22.4 MRI reconstruction showing a right-sided arch with anomalous left subclavian artery arising from a diverticulum of Kommerell. The ductal ligament will insert into the base of the diverticulum but does not show on the MRI.
Figure 22.5 Pulmonary artery sling: The left pulmonary artery arises as the first branch of the right pulmonary artery, encircling the trachea.
Between 50 and 67 per cent of cases present in the first year of life and are most commonly related to tracheal compression causing a stridor or ‘noisy breathing’. There may be a history of recurrent chest infections, or the stridor may be picked up on examination during one of these episodes. Younger children may have a characteristic ‘seal-bark’ cough, and older children may have a chronic non-productive cough due to tracheal irritation or have been mis-diagnosed as ‘asthmatic’. Severity of symptoms is variable, but generally, the more severe the compression, the earlier is the presentation. The stridor is not only due to the compression but also due to a degree of tracheo-broncho-malacia of the affected segment of the airway.
Oesophageal symptoms are less severe, but there may be a history of dysphagia. Infants may have been noticed to have frequent vomiting or drooling of saliva. However, the dysphagia is not usually severe enough to prevent normal nutrition or cause failure to thrive.