Right Aortic Arch With Mirror - Image Branching

Introduction

The aortic arch is a section of the aorta (the primary artery of the body). The aortic arch is present on the left side of the aorta. Various anomalies are associated with the aortic arch. The right aortic arch is an anomaly found in 0.01 to 0.1 percent of the general population. There are three main types of right aortic arch anomalies: Type I, RAA with mirror image branching (RAMI); type II—RAA with an aberrant left subclavian artery; and type III—RAA with an isolated subclavian artery. The subclavian artery is a large artery supplying the chest area.

What Is the Cause of the Right Aortic Arch with Mirror-Image Branching?

The cause of RAMI is congenital. The aortic arch usually passes over the left bronchus (a bronchus takes air into the lungs). A right aortic arch develops when the aortic arch traverses over the right bronchus. The aortic arch forms during the fourth week of embryonic development. However, various forms of the right aortic arch can evolve. The normal branching pattern of the aorta is the right innominate artery, the left common carotid, and the left subclavian artery. However, RAMI is a mirror image of normal anatomical branching.

How Common Is the Right Aortic Arch With Mirror-Image Branching?

About 60 percent of right aortic arch anomalies are RAMI. No underlying genetic abnormality is diagnosed in many patients with a right aortic arch. However, RAMI can be associated with DiGeorge syndrome (22q11 deletion) and congenital heart diseases (CHD) such as tetralogy of Fallot, truncus arteriosus, transposition of the great arteries, and tricuspid atresia (absence or narrowing of a body orifice).

1. DiGeorge Syndrome: It is a chromosomal disorder with heart anomalies and learning difficulties. Other findings include low blood calcium, poor immunity, and a cleft palate.

2. Truncus Arteriosus: It is diagnosed in early infancy. It is a complex congenital heart defect. It occurs when the aorta in the developing baby fails to separate during development. As a result, a connection remains between the aorta and the pulmonary artery.

3. Tetralogy of Fallot: It combines four CHDs: pulmonary valve stenosis (lung valve narrowing), ventricular septal defect (defect in the ventricles), right aortic arch, and right ventricular hypertrophy (thickening of the right ventricle).

4. Transposition of the Great Arteries (TGA): In this anomaly, the pulmonary artery and aorta switch positions. Nowadays, the survival rate for infants with TGA is more than 90 percent.

5. Tricuspid Atresia (TA): It is a heart birth defect where the tricuspid valve (the valve that connects the right atrium to the right ventricle of the heart) is absent. Many babies born with Down’s syndrome have TA.

What Are the Clinical Manifestations of the Right Aortic Arch with Mirror-Image Branching?

The symptoms of RAMI may depend on the patient's age.

1. Infants: RAMI is associated with CHD in more than 98 percent of patients. About 18 percent of children with CHD can have RAMI.

2. Adults: RAMI does not cause any heart, blood vessel, airway, or swallowing symptoms. However, vascular ring formation can pose some issues. A vascular ring is formed when the aorta forms a ring around the esophagus and trachea. A complete vascular ring leads to digestive and breathing problems. The symptoms include recurrent respiratory infections, wheezing, coughing, swallowing problems, feeding difficulties, and vomiting. However, vascular ring formation is rare in RAMI patients. Further, plaque deposition in the blood vessels or their abnormal dilatation is accompanied by the compression of the trachea or the esophagus.

How Is the Right Aortic Arch With Mirror-Image Branching Evaluated?

The cardiac examination in a patient with a right aortic arch is normal without CHD. However, an abnormal history and physical examination are needed if there are associated congenital heart defects. The pulmonary (lung) artery flow is abnormal in some cases. RAMI is incidentally found during routine imaging. RAMI evaluation can be done with the following investigations.

1. Chest X-Ray: A chest X-ray demonstrates a deviated trachea.

2. Barium Swallow: A barium swallow evaluation can demonstrate an esophageal indentation in patients with a vascular ring. However, a barium swallow is challenging to perform in children. Another disadvantage is the two-dimensional (2D) information.

3. Echocardiography: Echocardiography is the preferred imaging modality in children. It can also evaluate the aortic arch anatomy. However, it is operator-dependent. Also, it is challenging to perform this technique on complex cardiac anomalies.

4. Computed Tomography (CT): CT gives an accurate description of the surgical anatomy. It provides high spatial resolution in RAMI detection. CT scan is also beneficial for detecting vascular rings. The image can be converted into various planes to assess tracheal and esophageal compression simultaneously. New-generation scanners are available with radiation dose reduction technologies. Previously, during a cardiac CT, a scan was acquired during a specific portion of the cardiac cycle to reduce artifacts. This technique is called gating. Gating increases radiation exposure. CT is performed without gating, which further reduces exposure. However, a high-pitch spiral mode can reduce cardiac pulsation artifacts. Hence, CT may be performed without anesthesia or breath-holding in children. Contrast-enhanced CT (CECT) uses a dye for better image detection. However, the dye used is a disadvantage for children.

5. Magnetic Resonance Imaging (MRI) and Magnetic Resonance Angiography (MRA): MRI is an alternative to CT. The biggest advantage of MRI is the lack of radiation. Three-dimensional (3D) MRI provides a relationship between the aortic arch and the trachea and esophagus. But, MRI is time-consuming and requires general anesthesia in infants and children. However, compressed sensing, 3D ultra-short echo time, and 4D flow acquisition result in the scan time reduction. These result in less required sedation. But these modalities are not widely available. MRA provides excellent soft tissue contrast without contrast medium use. However, it is expensive and less available.

6. Angiography: The aortic root angiogram can show RAMI. Cardiac catheterization and angiography are done for aortic arch imaging. However, it is an invasive technique. Hence, this imaging modality is reserved for patients with other CHDs. Another indication is the CHDs that require blood flow information for cardiac treatment.

What Is the Management of the Right Aortic Arch With Mirror-Image Branching?

RAMI does not require medical or surgical therapy unless there is a significant left pulmonary abnormality. However, certain associated conditions require surgical correction.

1. Left Pulmonary Artery Stenosis: In the case of left pulmonary artery stenosis, a transcatheter balloon or angioplasty can be performed to remove the obstruction.

2. Vascular Ring Surgery: Surgery treats a vascular ring that compresses the trachea or esophagus. Surgery also helps prevent complications. The ring is split during the surgery.

Conclusion

RAMI is a rare congenital anomaly. Further, a RAMI diagnosis is uncommon in adulthood. Cardiac surgery is not done frequently in patients with congenital RAMI. However, a patient should visit a cardiologist regularly for careful monitoring and follow-up of the defect.