Right Aortic Arches

Etiology

In many patients, no underlying genetic abnormality is identified in patients with a right aortic arch; however, a right aortic arch can be associated with Digeorge syndrome (22q11 deletion) as well as conotruncal congenital heart defects such as tetralogy of Fallot, truncus arteriosus, and d-transposition of the great arteries.[3][4][5] Generally, three types of aortic arches exist in the literature as defined by the Edwards classification scheme. [6] These types are as follows:

1. Mirror image branching of the head and neck vessels. The first branch left the innominate artery, the second right carotid, and the third right subclavian.
   1. Most common (59%).
   2. Often associated with conotruncal congenital heart disease (truncus arteriosus and tetralogy of Fallot) 
2. Aberrant left subclavian artery from a diverticulum of Kommerell as a fourth branch from the aorta. The first branch is left carotid, second right carotid, and third right carotid.
   1. Second most common with a prevalence of approximately 40%.
   2. Not usually associated with congenital heart disease.
   3. Completes a vascular ring
3. Obliteration/isolation of the left subclavian artery with collateralization. Otherwise, the arch branching is similar to type 2.
   1. Third most common with a prevalence of 1.5%.

Epidemiology

A right aortic arch occurs when the aortic arch traverses over the right bronchus instead of the left bronchus (which defines a left aortic arch). Embryologically, this develops when the right dorsal aorta persists and the left dorsal aorta regresses. Depending on the formation of the other branches of the aortic arch, various forms of the right aortic arch can develop. This includes a mirror type right aortic arch, defined by the first branch originating from the aorta being the left innominate artery, the second being the right common carotid artery, and the third being the right subclavian artery. This branching pattern is similar to the normal anatomical branching seen in the general population, however, in a mirror image. The ductus arteriosus in this scenario originates off the underside of the aortic arch or from the left innominate artery, which predisposes patients to left pulmonary artery stenosis or even isolation. In type 2 right-sided aortic arch, the first branch off the aorta is the left common carotid artery, followed by the left common carotid artery, right subclavian artery, and finally the left subclavian artery. If an aberrant left subclavian is present (type 2 aortic arch), the ductus arteriosus originates from this subclavian artery, which leads to an outpouching of the aorta (diverticulum of Kommerell). After the closure of the ductus arteriosus connection to the left pulmonary artery, and due to a retroesophageal course of the left subclavian artery, a vascular ring circumscribing the esophagus, causing am esophageal stricture. An extremely rare form of a right aortic arch with isolation of the left subclavian from a ductal attachment to the left pulmonary artery can occur. Rarely, a double aortic arch with an atretic left segment can be misdiagnosed as a right aortic arch. This differentiation is very important as the expected symptomatology, and surgical treatment are different.[7][8][9][2]

Pathophysiology

The right aortic arch with mirror image branching does not cause any cardiovascular, airway, or swallowing symptoms. It can be associated with left pulmonary artery flow abnormalities, especially if a left ductus from the innominate artery was present. Right aortic arch with an aberrant left subclavian causes a vascular ring can be associated with swallowing difficulties (dysphagia lusoria) in children after they begin to eat solid foods, especially meat. Rarely, it can be associated with stridor and recurrent croup if there are compression and malacia of the trachea; however, this symptomatology is more common in double aortic arches.[10][11]

History and Physical

History and physical examination show abnormalities associated with an underlying intracardiac congenital heart defect such as tetralogy of Fallot or truncus arteriosus. Without an underlying intracardiac congenital heart defect, the cardiac physical examination in a patient with a right aortic arch is normal. Symptoms of a vascular ring include a history of recurrent croup and an examination finding of stridor, more often noted in double aortic arch forms of vascular rings. The history of dysphagia is a more common finding in the right aortic arch and aberrant left subclavian form of a vascular ring. In "loose vascular rings," the patient could remain asymptomatic over their lifetime.[10][11]

Evaluation

A chest x-ray can demonstrate the trachea deviated to the left in the presence of a right aortic arch. This occurs from the aortic arch crossing over the right bronchus instead of the more common right-sided deviation from a left-sided aortic arch. A barium swallow evaluation can demonstrate a posterior esophageal indentation from the aberrant left subclavian in patients with a vascular ring. An echocardiogram evaluation will demonstrate any associated intracardiac abnormalities and can demonstrate arch sidedness, including the anatomy of the arch. By echocardiography, the first branch of the aorta defines the sidedness of the aortic arch. If the first branch of the aorta bifurcates to the left, then a right aortic arch is present. CT scans can be performed when there is a concern for a vascular ring causing important symptoms. This can be helpful in preoperative surgical planning, but it should be reserved for patients in whom vascular ring surgery is considered. CT scans can also demonstrate the airway and esophagus and yield an anatomic evaluation of narrowing or compression of these structures. [12] MRI of the aorta can be performed en lieu of a CT scan to avoid a potential long-term radiation risk. Cardiac catheterization and angiography can be performed to image the aortic arch. However, due to its invasiveness, this imaging modality is reserved for patients with other congenital heart defects that require hemodynamic information of cardiac interventions. 

Treatment / Management

A patient symptomatic from a right aortic arch with an aberrant right subclavian (vascular ring) can undergo surgical division of the ligamentum arteriosus with plication of the diverticulum of Kommerell off of the esophagus. If stridor secondary to tracheomalacia is present, this symptom might not fully resolve immediately after surgery. Right aortic arch with mirror imaging branching does not typically require medical or surgical therapy unless an important left pulmonary abnormality is noted. In the case of left pulmonary artery stenosis, a transcatheter balloon or stent angioplasty intervention can be performed to alleviate the stenosis. In the scenario of left pulmonary artery isolation, a strategy of left pulmonary artery rehabilitation and reimplantation can be employed. Surgical treatment of a vascular ring is rarely associated with long-term morbidity. However, there is a small surgical risk of recurrent laryngeal nerve injury and vocal cord paralysis, as well as thoracic duct injury, leading to chylous pleural effusions.[13][14][15](B3)

Differential Diagnosis

When a right aortic arch is identified, it is important to be confident of the branching pattern of the aortic arch to counsel families and patients regarding the propensity to develop symptoms. In general, patients with congenital heart defects would have symptoms as a neonate or infant that would be more concerning than the symptoms associated with a vascular ring. Feeding and swallowing difficulties in children would be more commonly associated with reflux. Respiratory symptoms, which are less common with a right aortic arch, would be common in asthma, croup, or laryngomalacia.