Note the following timeline:
1737 - Hommel published the first description of a double aortic arch.
1794 - Bayford described the first retroesophageal right subclavian artery.
1932 - Maude Abbott described 5 cases of double aortic arch for which surgical therapy was considered.
1945 - Gross performed the first successful division of a double aortic arch and used the term vascular ring for the first time in the article that he wrote describing the procedure in the New England Journal of Medicine.
Vascular ring is an anomalous configuration of the aortic arch and/or associated vessels that forms a complete ring around the trachea or esophagus.
This anomaly occurs early in embryologic development and occurs in many forms. Vascular rings result from incomplete regression of 1 of 6 embryonic branchial arches. The deletion of chromosome region 22q11 appears to be closely associated with these anomalies.
Early in development, a dorsal and ventral aortic arch is present. Six embryonic branchial arches connect the 2 arches. The third, fourth, and sixth arches are crucial in the development of the aortic arch, its major branches, the ductus arteriosus, and the pulmonary artery. In normal development, each arch develops into a vascular structure or involutes in the following manner:
The right and left first and second arches develop into a portion of the arterial supply of the face.
The third arches form the carotid arteries.
The dorsal aorta between the third and fourth arches involutes.
The fourth arches are the main contributors to the aortic arch. The proximal right fourth arch develops into the right subclavian artery. The left fourth arch remains as the aortic arch.
The fifth arch involutes bilaterally.
The ventral sixth arch develops into the proximal right pulmonary artery. The ventral left sixth arch develops into the left pulmonary artery, while the dorsal portion becomes the ductus arteriosus.
The seventh segmental arterial branches of the dorsal aorta form the left subclavian artery and the distal right subclavian artery.
Double aortic arch
The double aortic arch develops when the distal right fourth arch does not involute. The fourth right and left arches persist and join the left-sided descending aorta, forming a complete ring. In 30% of patients who have this anomaly, the less dominant arch is atretic. The double aortic arch and right aortic arch with aberrant left subclavian artery are the 2 most common forms of vascular rings. The mature anatomy of a vascular ring formed by a right aortic arch with an aberrant left subclavian artery is shown in the image below.
Together, these 2 anomalies account for 85-95% of all vascular rings.
Right aortic arch anomalies
When the right fourth branchial arch remains, a right aortic arch is present. This may exist in the absence of other anomalies. Persistence of the right arch with involution of the left is associated with variations in the origin of the left subclavian artery and ductus arteriosus. Some of these configurations can produce a vascular ring.
Right aortic arch with aberrant left subclavian artery and left ligamentum arteriosum
In this abnormality, the right arch gives off the left carotid artery first. This travels anterior to the trachea. The right carotid, right subclavian, and left subclavian arteries then follow in sequence. These take a retroesophageal position, giving rise to the ligamentum arteriosum from its base. The position that the ligamentum occupies in relation to the pulmonary artery completes the ring.
Left aortic arch with right descending aorta and right ligamentum arteriosum
The first arch vessel to exit in this complex is the right common carotid artery, which then passes anterior to the trachea. The left carotid and left subclavian then follow. The right subclavian artery arises more distally as a branch of the proximal right-sided descending aorta. The ligamentum arteriosum arises from the base of the right subclavian artery and travels to the right pulmonary artery.
Left aortic arch with right descending aorta and atretic right aortic arch
In this abnormality, the brachiocephalic vessels arise from the left-sided arch in the normal arrangement. The left arch then passes behind the esophagus to join a right-sided descending aorta. An atretic right arch is present and completes the ring.
Anomalous innominate artery (brachiocephalic [arterial] trunk)
When an anatomic abnormality of the innominate artery is noted, the innominate artery appears to originate from a distal and leftward position on the arch (instead of originating from the right side of the arch). As it courses from left to right, it crosses the trachea anteriorly and may produce compression of the same.
Retroesophageal right subclavian artery with left aortic arch and left ligamentum arteriosum
This is the most common arch vessel anomaly. The right subclavian artery originates as the last brachiocephalic branch from the descending aorta and runs in the retroesophageal position. The ligamentum arteriosum is often normally positioned.
Right aortic arch with mirror-image branching and retroesophageal ligamentum arteriosum
In this anomaly, part of the distal left fourth arch remains. The left innominate, left carotid, and left subclavian arteries course anterior to the trachea. Following these, the right carotid and right subclavian arteries arise. The ligamentum is the last to arise in this sequence; it passes leftward, behind the esophagus, and then travels anteriorly to join with the left pulmonary artery to complete the ring.
Vascular rings produce symptoms and physical findings consistent with airway or esophageal compression. The vast majority of vascular rings produce symptoms that arise in infancy and childhood. The child commonly presents with stridor, cyanosis, respiratory distress, apnea, or a brassy cough. The child also may present with a history of asthma, recurrent pneumonia, weight loss, and difficulty feeding. GI symptoms of vascular ring are more common later in life than at this time. Some patients with complete vascular rings present with minimal or no symptoms.
Chest radiography is the first and most commonly performed test. The position of the aortic arch can be identified.  Compression of the trachea and lobar atelectasis can also be identified. A specific finding associated with anomalous left pulmonary artery is hyperinflation of the right lung.
Results of barium esophagography are diagnostic in most cases. Posterior compression of the esophagus is associated with a double aortic arch. Anterior compression of the esophagus is associated with an anomalous left pulmonary artery.
MRI is becoming the diagnostic test of choice for evaluating vascular ring anatomy.  MRI provides sensitivity and specificity with excellent anatomic definition; although the use of toxic contrast agents is not required, general anesthesia is required.  Smith et al recently reviewed the current role of MRI in the evaluation of vascular rings and pulmonary artery slings. 
CT scanning of the vascular anatomy is also reliable and accurate.  Although this imaging modality requires the use of ionizing radiation, there is no anesthesia risk as for cardiac MRI and it is more accurate in the evaluation of the tracheobronchial anatomy. 
Cardiac catheterization and aortic angiography are reserved for cases in which complex congenital cardiac anomalies are present with the vascular ring pathology
Bronchoscopy is used to evaluate children with symptoms or airway obstruction or compression. In cases of an abnormally placed innominate artery, pulsation is observed on the anterior wall of the trachea corresponding to the area of compression.
Symptomatic vascular rings are treated with surgery, which should be performed promptly after diagnosis, especially in patients with symptoms of airway compromise.
The left thoracotomy approach can be used to address most vascular ring anomalies; however, the surgeon must have a complete delineation of the vascular ring anatomy and the associated tracheal or cardiac anomalies present.
Because airway problems associated with vascular rings can cause severe complications, preoperative airway management is extremely important.
If the thoracotomy approach is chosen, a muscle-sparing incision is preferred. When the thorax is entered, all anatomic features of the vascular ring should be identified before the structures are divided. The phrenic, vagus, and recurrent laryngeal nerves should be identified and preserved.
Communication between the surgeon and anesthesiologist is essential during the surgical procedure. The placing of clamps before division of vascular structures temporarily increases the constriction effect of the ring, and airway constriction may increase during this time. The surgeon should announce the application of the clamp, forewarning the anesthesiologist that oxygenation may deteriorate or that ventilation may transiently become difficult.
In patients with double aortic arch in whom a patent arch is divided, pulse oximetry and monitoring of blood pressure in both upper extremities is useful. These measurements help to confirm the vascular anatomy.
Division of a double aortic arch
The left side of the chest is entered through the fourth intercostal space. The pleura is opened, and the components of the vascular ring are visualized. The right or posterior arch does not need to be mobilized unless it is the arch to be divided. In such cases, the proximal descending aorta is reflected anteriorly to visualize where the right arch enters. The nondominant or smaller arch is divided. A likely site for division of the minor or atretic arch is at its juncture with the descending aorta. Division should be performed between applied vascular clamps, and the ends should be oversewn with fine nonabsorbable vascular suture. The ligamentum arteriosum and any other fibrous bands around the trachea or esophagus in the area also should be divided.
Division of a vascular ring with right aortic arch anatomy
The primary structure to be divided is the ligamentum arteriosum. After left thoracotomy is performed, the anatomy should be clearly visualized and defined. The ligamentum is identified and divided between vascular clamps.
Repair of anomalous left pulmonary artery
Many surgeons approach this anomaly with a median sternotomy and perform cardiopulmonary bypass. Aortic and single atrial cannulation is used. The child is cooled to 32°C, and a normal cardiac rhythm is maintained.
The left pulmonary artery is identified at its junction with the right and is dissected as far to the left as possible. Its origin is often on the posterior surface of the right pulmonary artery and to the right of the trachea. The pericardium is opened on the posterior left side near where the ligamentum arteriosum meets the pulmonary artery. The left pulmonary artery is identified and freed. A partially occluding clamp is applied on the right pulmonary artery at the junction with the left pulmonary artery, and the left pulmonary artery is transected.
The orifice of the left on the right pulmonary artery is closed primarily with fine, interrupted nonabsorbable suture. The partially occluding clamp is released and posteriorly placed on the main pulmonary artery. An arteriotomy is made, and the divided left pulmonary artery is brought through a path behind the trachea and sewn to the main pulmonary artery.
Tracheal anomalies associated with an anomalous left pulmonary artery
The usual tracheal anomaly associated with an anomalous left pulmonary artery is tracheal stenosis. The choice of repair depends on the length of the trachea involved. Resection with end-to-end anastomosis is used for short segments, whereas tracheoplasty is used for long-segment anomalies.
In a retrospective review (1986-2011) of 20 Australian pediatric patients with severe tracheal stenosis, including 12 pulmonary artery sling and 6 with coexisting congenital intracardiac anomalies, Yong et al reported the advent of slide tracheoplasty, a multidisciplinary team approach, and abandonment of patch tracheoplasty improved survival rates, with survival beyond 2 years predictive for an excellent outcome. 
Abnormally placed innominate artery
Tracheal compression from this problem usually is approached through a right anterolateral thoracotomy. The right lobe of the thymus is removed. The pericardium is opened, and the innominate artery is identified near its junction with the aorta. The innominate artery is secured to the posterior periosteal layer of the sternum using interrupted nonabsorbable suture. The suture is passed through the adventitia of the innominate artery and through the periosteal layer of the sternum. Three sutures are usually used.
Video-assisted thoracic surgical (VATS) techniques have been used to approach these anomalies. The application of VATS is currently limited to the division of an atretic arch or a ligamentum arteriosum.
Complications related to surgical intervention include injury to the phrenic, vagus, or recurrent laryngeal nerves. Disruption of the thoracic duct with a resultant chylothorax also can occur. Late vascular complications, such as subclavian steal, may be noted in cases in which division of the brachiocephalic vessel was necessary.
In some patients, airway compromise may persist after surgical intervention. This compromise may be secondary to tracheomalacia and may require tracheal resection of the damaged segment to alleviate the problem.
Outcomes And Prognosis
Approximately 95% of patients undergoing operative correction of an isolated vascular ring anomaly have a normal lifespan and are asymptomatic. Patients with less-than-optimal long-term results are those with anomalous left pulmonary artery with and without complete tracheal rings and those with severe associated intracardiac defects.
Some patients continue to have abnormal pulmonary function years after surgery. Also, many patients continue to have pronounced bronchial responsiveness to histamines years after surgery.