An aberrant right subclavian artery (ARSA) is a congenital variation in which the large artery supplying the right arm branches off the aorta in an unusual location, then crosses behind the esophagus to reach the right side of the body. It affects roughly 0.5% to 2.2% of the general population, making it the most common congenital anomaly of the aortic arch. Most people with this variation never know they have it, but in some cases it compresses the esophagus or airway enough to cause symptoms.
How the Artery Develops Differently
In a typical anatomy, the aorta (the body’s main artery) gives off branches in a predictable order. The right subclavian artery normally forms early in fetal development when certain embryonic vessel segments fuse together on the right side. In ARSA, one of those segments (the right fourth aortic arch) fails to develop properly and instead dissolves. The artery that would become the right subclavian persists but now originates directly from the descending aorta, well past its normal takeoff point.
Because it arises from the wrong spot, the artery has to travel across the chest to reach the right arm. In most cases, it passes behind the esophagus. Less commonly, it runs between the esophagus and the trachea, or in front of the trachea. This retroesophageal course is what sets the stage for potential compression symptoms later in life.
Why It’s Flagged on Prenatal Ultrasound
ARSA is one of the “soft markers” that can appear on a routine fetal ultrasound, typically during the second trimester. When it shows up, it naturally raises concern about chromosomal conditions, particularly Down syndrome and DiGeorge syndrome (22q11.2 deletion). A study of 340 fetuses diagnosed with ARSA found that when ARSA was the only unusual finding, the rate of clinically significant chromosomal abnormalities was just 2.5%. That number climbed to 14.3% when other soft markers were also present, and to 16.4% when additional structural abnormalities were detected.
Among all the chromosomal findings in that study, Down syndrome and DiGeorge syndrome together accounted for nearly half. So while an isolated ARSA on an otherwise normal ultrasound carries a low risk, doctors typically recommend further genetic testing (amniocentesis or similar) to rule out these conditions, especially when other markers are present. For the vast majority of pregnancies where ARSA appears alone with no other findings, the outcome is a healthy baby with a harmless anatomical variant.
Symptoms in Infants vs. Adults
ARSA affects infants and adults differently because of how the surrounding structures change with age. In babies, the trachea is soft and compressible, so the aberrant artery is more likely to press on the airway. This can cause wheezing, stridor (a high-pitched breathing sound), recurrent pneumonia, or episodes where the skin turns bluish. These respiratory symptoms are the hallmark of ARSA in young children.
In adults, the trachea is rigid enough to resist compression, so symptoms tend to involve the esophagus instead. The classic problem is difficulty swallowing, a condition called dysphagia lusoria. This can develop at any age but often worsens later in life as the aberrant artery stiffens and enlarges with atherosclerosis. Some people describe a sensation of food getting stuck behind the breastbone, particularly with solid foods. The swallowing difficulty can range from mild and occasional to persistent enough to affect nutrition.
Kommerell Diverticulum and Aneurysm Risk
At the point where the aberrant artery branches off the aorta, a bulge can form called a Kommerell diverticulum. This outpouching is present in an estimated 20% to 60% of people with an aberrant subclavian artery. It’s defined as the origin of the artery being more than 50% wider than the artery’s normal downstream diameter.
This matters because Kommerell diverticula carry a real risk of dissection (a tear in the vessel wall) or rupture. One review of case reports found aortic dissection rates between 19% and 53% in patients with this finding. Separately, when aberrant right subclavian arteries become aneurysmal (ballooned out), which happens in up to 60% of affected patients over time, the mortality rate after rupture is around 50%.
Because of these risks, vascular specialists generally recommend surgical repair when the diverticulum’s opening exceeds 30 mm in diameter, even if the patient has no symptoms. Smaller diverticula without symptoms are monitored with regular imaging to watch for growth.
How It’s Diagnosed
Many cases of ARSA are discovered incidentally during imaging done for unrelated reasons. When swallowing symptoms are present, the workup often starts with a barium swallow, which shows a characteristic indentation on the back wall of the esophagus at the level of the aortic arch. This posterior compression pattern is a classic clue.
CT angiography is the primary tool for confirming the diagnosis and planning any intervention. It provides detailed images of the artery’s course, shows whether it’s compressing the esophagus, and reveals the size of any Kommerell diverticulum. MRI can also visualize the anatomy without radiation exposure, making it a useful alternative for younger patients or for ongoing surveillance.
How ARSA Differs From Vascular Rings
ARSA is classified as an incomplete vascular ring, meaning it does not fully encircle the trachea and esophagus. Complete vascular rings, such as a double aortic arch or a right-sided aortic arch with an aberrant left subclavian artery, wrap entirely around both structures and tend to cause more severe compression symptoms at an earlier age. A double aortic arch, for instance, typically presents in infancy with significant breathing problems, while ARSA may go unnoticed for decades. This distinction matters because complete vascular rings almost always need surgical correction, whereas most people with ARSA never require treatment.
Treatment Options
The majority of people with ARSA need no treatment at all. Intervention is reserved for those with significant swallowing or breathing symptoms, or for those with a Kommerell diverticulum large enough to pose a rupture risk.
When surgery is needed, the general approach involves two steps: rerouting blood flow to the right arm (usually by connecting the right subclavian artery to the nearby right carotid artery through an incision in the neck) and then closing off the abnormal origin of the artery from the aorta. This second step can be done through open surgery, with an endovascular stent graft placed inside the aorta, or using a hybrid approach that combines both. More recently, robotic-assisted techniques have been used in select patients whose artery origin isn’t heavily calcified or aneurysmal.
There is no single gold-standard technique. The choice depends on the patient’s anatomy, the size of any diverticulum, and the surgical team’s experience. Women are affected roughly two to three times more often than men, though the reasons for this difference remain unclear.