The term "vascular ring" (VR) refers to the vascular structures that encircle and compress the esophagus and trachea, causing respiratory and gastrointestinal symptoms. VRs are further divided into two broad categories: complete or incomplete.
Complete VRs encircle the trachea and esophagus entirely. These include double aortic arch (DAA) and right aortic arch (RAA) with an aberrant (retro-esophageal) left subclavian artery. These are the most common types of vascular rings.. Incomplete VRs do not completely encircle the trachea and esophagus, although some compress either the trachea or esophagus. It usually includes aberrant innominate artery, aberrant right subclavian artery, and pulmonary artery sling.
An arch sidedness is defined by the position of the aortic arch in relation to the trachea and the bronchi. A left aortic arch would be towards the left of the trachea and run over the left bronchus, whereas an RAA would be towards the right of the trachea and run over the right bronchus. A DAA is when there are two transverse aortic arches running over the trachea and both bronchi. Normally, the arch sidedness is towards the left, and there is no arterial duct behind the trachea or esophagus. In cases of the vascular ring, there is a patent vessel, an atretic vessel, or its remnants circling the trachea or esophagus.
DAA can be further divided into three main types. The most common is the dominant RAA with a smaller LAA (80%). The dominant LAA is found in 10% and equal aortic arches in the rest 10%.
Depending on the site of the regression of the fourth aortic arch, RAA can be divided into 2 parts. If regression is proximal to the left subclavian artery, it is called RAA with an aberrant (retro esophageal) left subclavian artery. If regression is distal, it is called RAA with mirror image branching. Around 50% of cases of right-sided aortic arch are associated with an aberrant (retro-esophageal) left subclavian artery. This often has a Kommerell diverticulum named after the radiologist Dr. Burckhard F. Komerell, who reported this finding in 1936. Kommerell diverticulum is an outpouching of the distal aorta and usually originates from the left arch.
Pulmonary artery sling occurs when the left pulmonary artery originates from the right pulmonary artery, which crosses between the trachea and esophagus before entering the left lung and thus compressing the trachea. It is the only type of VR which has an indentation in the anterior esophagus on barium swallow.
Anomalous innominate artery originates later from the transverse arch and then crosses the trachea causing anterior tracheal compression.
According to the International Congenital Heart Surgery Nomenclature and Database Committee, the classification system for vascular rings is as follows:
A. Complete vascular rings
1. Double aortic arch (DAA)
I. Dominant right arch
II. Dominant left arch
III. Equal arches/balanced arches
2. Right aortic arch (RAA)
I. RAA+ aberrant left subclavian artery (ALSA)
II. RAA with mirror imaging
B. Incomplete aortic arch
1. Innominate artery compression syndrome
2. Pulmonary artery sling
3. Aberrant right subclavian artery (ARSA)
The exact cause of DAA is not yet known nor for any other VR. There have been associations of RAA and DAA with 22q11 deletion in the literature. There is some association of DAA with trisomy 21 and trisomy 18. A left aortic arch with aberrant (retro-esophageal) right subclavian artery is not a ring, but is highly associated with trisomy 21.
The first diagram below is a caudad view (looking from top to bottom) through a cartoon of a toti-potential arch. This arch DAA with bilateral ductus arteriosi was identified in one patient with transposition. It has both arches and bilateral ductus arteriosi. As far as we can tell, there has not been a DAA with bilateral ductus arteriosi with a normal heart. The second diagram is the usual one from a person with a double aortic arch; however, there is usually a left ductus or ligamentum. It is rare for the DAA to have a right ductus or ligamentum. The final diagram is a right aortic arch with an aberrant (retro esophageal) left subclavian artery. With this, there is a regression of the IV aortic arch on the left. The first vessel from the ascending aorta is a left carotid artery, next, a right carotid artery, then a right subclavian artery, and finally, the aberrant (retro esophageal) left subclavian artery. The part between the left subclavian artery and the descending aorta is the diverticulum of Komerell.
Double aortic arch is rare. whereas the incidence of RAA in the general population is more common at 0.1%. In one of the studies, DAA is the most common cause of vascular ring accounting for 55% of the cases, whereas RAA with aberrant left subclavian artery is 45%. The incidence of DAA in 22q11 deletion is 14%, in which 17% are right arch dominant, whereas the incidence of RAA in 22q11 deletion is 30%. There is a male predominance, with around 67% of the cases being male in one of the studies.
Kommerell Diverticulum can have possible 2 scenarios: left aortic arch with aberrant right subclavian artery seen in 0.5% to 2% of the population. The second one can be the right aortic arch with aberrant left subclavian artery seen in 0.05% to 0.1% of the population.
In DAA, the ascending aorta further divides into right and left transverse arches. The right transverse arch courses over the right mainstem bronchus whereas the left aortic arch courses over the left mainstem bronchus. Because the aorta usually descends down towards the left side of the body, the right aortic arch goes posteriorly and inserts into it. Further branches originate from the transverse arches: left common carotid and subclavian from the left aortic arch and the right common carotid and right subclavian from the right arch. The arterial duct is usually left-sided and generally inserts in the left transverse arch or descending aorta. 
The vascular ring is formed when there is a failure of the regression or persistence of some part of the aortic arch.  A double aortic arch is formed when both the fourth aortic arches persist.  Ascending aorta and transverse aortic arch compress the trachea whereas the right aortic arch compresses the esophagus.  In three-fourths of patients with a double aortic arch, the right arch is dominant.  Double aortic arch is sometimes associated with other congenital heart defects including ventricular septal defects in about 10% of the patients, atrial septal defect in about 5% of the patients, tetralogy of Fallot in about 4% of the patients and in rare cases with truncus and transposition of the great vessels.
Many patients with DAA have earlier presentations as compared to patients with other types of Vascular rings, most of them presenting in early infancy and almost all of them before three years of age. The most common presentation is respiratory, which is seen in around 91% of the patients and includes symptoms of stridor, wheezing, coughing, or choking. Around 40% of patients presented with gastrointestinal symptoms like choking with feeds, dysphagia, and failure to thrive. About 30% of the patients presented with cardiac symptoms like a murmur, cyanosis, or chest pain.
In patients with a RAA with aberrant (retro-esophageal) left subclavian artery, it is considered a "looser ring" than a DAA. These patients usually have more problems with dysphagia. When they are babies, they can take milk easily. However, once they start taking solid foods, that is where the symptoms arrive. Many of these patients are not diagnosed until the teenage years when the guardians complain that the patient is the last to leave the dinner table. This is because the patient is chewing their food so that they can swallow without it hurting. Most do not realize that they are doing that.
Prenatally, the diagnosis can be confirmed with a fetal echocardiogram.
Postnatally, other than confirming a suspected diagnosis, the purpose of testing is for side determination. This would be beneficial to decide whether to perform a thoracotomy from either left or right side. The initial evaluation is generally done using a chest radiograph, which shows narrow airways in 47% of patients and the dominant right arch in 40% of the patients.  Esophagography or barium swallow can be done, which shows a posterior indentation of the esophagus in around 74% of the patients. CT and MRI are 100% sensitive for diagnosing DAA. MRI has replaced CT angiogram and cardiac catheterization for superior diagnosis and noninvasive technique in older children. The risk of general anesthesia for a child or infant who cannot breath-hold needs to be weighed against the radiation from a CT scan, which can be accomplished in seconds. Many modern CT scans use less radiation than prior CT scans, and the CT scan is better at delineating the tracheobronchial tree. Echocardiography with Doppler and color mapping is noninvasive and convenient. The echocardiogram can also be used to evaluate any additional cardiac pathology before surgery.
Most patients need surgical intervention, which is earlier in cases of DAA, around 1.4 months after the presentation and 4.9 months after being symptomatic. The site of operation depends on the nondominant arch, which is generally left-sided in around 71% of the patients. So, lateral thoracotomy via the left side is usually performed. This is followed by ligating and dividing the small arch and then ligating and dividing the ductus arteriosus or ligament arteriosus. This is then accompanied by the complete mobilization of the trachea and esophagus. For patients with a Kommerell diverticulum, many surgeons will resect the diverticulum and reimplant the left subclavian artery, end to side, with the left common carotid artery.
Alternatively, there is a minimally invasive surgery using video-assisted thoracoscopic techniques division of vascular ring, which seems safe and effective in children.
The vascular ring should be differentiated from conditions that can present with similar complaints. These include congenital tracheal anomalies like tracheoesophageal fistula or tracheomalacia. It can also present like congenital laryngeal problems such as laryngomalacia, laryngeal webs or cysts, or external compression of the trachea with a mass like a lymphoma. Other things to keep in mind are common conditions like asthma, gastro-esophageal reflux, or recurrent pneumonia.
Postoperative complications are uncommon: chylothorax in 9% of the patients, transient hypertension in 4%, and vocal cord paralysis/paresis in 3% of patients. There have been some cases of aortoesophageal fistula in one study. The presentation of these patients was with copious gastrointestinal bleeding, which was relieved with an esophageal balloon catheter waiting for surgery. Many patients will still have problems with stridor after the operations for a while. This is because the trachea was not able to develop appropriately in utero or post-natally. It will take time for the patient to develop a stronger trachea and sometimes may even require an additional intervention to elevate the aorta off of the trachea.
The median time between surgery and discharge from ICU was two days, whereas discharge from hospital was 5 to 8 days. Most patients remain asymptomatic after surgery in one of the studies. Whereas most of the studies have shown that respiratory symptoms were the most common chronic symptoms seen in these patients. The continued presence of symptoms has been related to tracheomalacia and tracheostenosis, generally due to the anomalous development of the trachea.
Double aortic arch presents at a younger age as compared to RAA with aberrant (retro esophageal) left subclavian artery. Most infants have a full recovery without complications.
The vascular ring is an uncommon diagnosis. DAA is an important cause of vascular ring, which generally causes symptoms in the newborn age group. Although cardiologists generally diagnosis the condition, it is first seen by the neonatologist as soon as the baby is born. The nurses are a vital part of the group who help diagnose the condition, based on the vital signs, respiratory and feeding difficulties. Radiologist plays a very important part in diagnosing the condition. The pharmacist is also a crucial part of the team, as the baby would need to be given nothing by mouth, and adequate fluids to be given by the venous route when planning for surgery. Ultimately, the surgeon is the one who would perform the surgery based on the information from all the members of the team.
A critical part of the post-surgery care is the intensivist, who takes care of the patient and then transfers to the pediatrician, who then follows the patient for any complications. There is definitive evidence to recommend the type of imaging and treatment. [Level 1]
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