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Features Departments Information |
  Carl Lewis Backer, MD  Constantine Mavroudis, MD |
Vascular rings CARL LEWIS BACKER, MD aSpring 1998 THE HISTORY OF surgery for children with vascular rings is intimately tied to Children's Memorial Hospital and the divisions of Cardiovascular-Thoracic Surgery and Otolaryngology. This has led to the development of a program with national and international referrals, resulting in the largest published single institutional experience with vascular rings in North America—more than 300 patients! The remarkable historical events in vascular ring surgery are shown in Table 1. Two of the four significant events have taken place at Children's Memorial.
The phrase "vascular ring" was first used by Dr. Robert Gross (Chief of Surgery, Boston Children's Hospital, 1947 to 1967) in his report describing the first successful division of a double aortic arch in 1945.1 In that manuscript, Gross recalled his observations at the time of an autopsy he performed in 1931. A ring of blood vessels was found encircling the intrathoracic portion of the esophagus and trachea in such a way that the esophagus was indented from behind, whereas the trachea was compressed on its anterior surface. The pathologic findings at once suggested that a division of some part of the so-called vascular ring during life would probably have relieved some of the pressure on the constricted esophagus and trachea. Since Gross' original description, the phrase "vascular ring" has been used to refer to a collection of congenital vascular anomalies that encircle and compress the esophagus and trachea. In that original report Gross described the two classic vascular rings: right aortic arch with left ligamentum and divided aortic arch (now called double aortic arch). In 1948, Gross reported successful suspension of the innominate artery to the sternum for innominate artery compression syndrome in a 4-month-old infant with wheezing and respiratory distress. In 1954, Willis J. Potts and Paul Holinger (Chief of Bronchology, CMH, 1937 to 1972) coined the term "pulmonary artery sling" when they reported the first successful repair of this anomaly in a 5-month old with wheezing and intermittent attacks of dyspnea and cyanosis.2 Although innominate artery compression syndrome and pulmonary artery sling are not complete anatomic "rings," they are classified with the classic vascular rings because of the similarities in patient presentation, diagnosis, and surgical therapy. Complete tracheal rings occur in 50% of patients with pulmonary artery sling and hence their inclusion with vascular rings. The most recent historic milestone in vascular ring surgery occurred in 1982 when Farouk S. Idriss reported the first successful use of pericardium to open the stenotic trachea of a child with complete tracheal rings.3
Embryology Vascular rings are a group of congenital anomalies caused by different regressions and involutons from the embryonic aortic arch system. A simplified version of the development of these anomalies is shown in Figure 1. In the embryonic aortic arch system, the ventral and dorsal aorta are connected by six primitive aortic arches. The first, second, and fifth arches involute to form Edward's classic double aortic arch. If the right fourth arch involutes, a normal left arch is formed. If the left fourth arch involutes, a right aortic arch is formed.  FIGURE 1 Progression of the embryonic aortic arch system to a double aortic arch, right aortic arch, or normal left arch. Clinical presentation and diagnosis In the fifty years between 1947 and 1997, 301 children have undergone surgical repair of vascular rings or tracheal rings at Children's Memorial. This series was first reported by Hisashi Nikaidoh from the Division of Cardiovascular-Thoracic Surgery in 1972 (68 children).4 The series was updated in 1989 (204 children)5 and again in 1996 (293 children).6 The current total numbers of children that have undergone surgical repair of the various vascular and tracheal rings in the division as of 1997 are shown in Table 2. Although there have been several different classification schemes proposed for vascular rings, we have preferred to simply call each vascular ring by its anatomical description rather than using a complex (and hard to remember!) numbering or alphabetic lettering system. The classic symptom of a child with a vascular ring is the "seal-bark" cough. Other symptoms include stridor (noisy breathing), asthma, recurrent pneumonia, and cyanotic spells. Apnea is a common symptom in children with the innominate artery compression syndrome. Children with a pulmonary artery sling and/or complete tracheal rings often have severe respiratory distress requiring emergent intubation and ventilation. Dysphagia tends to occur as a symptom only in older children taking solid foods. Vascular rings are rare in the overall spectrum of diseases that cause respiratory symptoms in children, and their diagnosis requires a heightened index of suspicion. The diagnosis of a vascular ring requires a sequential evaluation of the child.7 Once the diagnosis of a vascular ring has been made, it is important to resist the temptation to continue obtaining different studies that simply reconfirm the diagnosis. Examinations that may lead to the correct diagnosis include chest radiograph, barium esophagram, bronchoscopy, echocardiogram, CT/MRI scans, and angiography. The chest radiograph can usually establish the location of the aortic arch—normal left, right, or indeterminate (double aortic arch). The trachea should be closely inspected on both the AP and lateral views for tracheal compression. This can be highlighted with high-kV films of the airway. Hyperinflation of the right lung is common in patients with pulmonary artery sling.   FIGURE 2. Barium esophagram in a 13-month old child with a double aortic arch. (left: antero-posterior, and right: lateral). The barium esophagram is the single most important and reliable technique for making the diagnosis of a vascular ring. It is also relatively inexpensive in the current era of heightened cost awareness. If the child has classic symptoms and a barium swallow that shows typical compression of the esophagus, we can proceed to surgical intervention without further studies. An example of a barium esophagram in a child with a double aortic arch (AP/lateral) is shown in Figure 2. The compression of the esophagus is persistent in all views, differentiating it from a peristaltic wave. Pulmonary artery sling is the only vascular ring which causes anterior compression of the esophagus with no posterior component. Barium esophagram is normal in patients with innominate artery compression syndrome. Although the barium swallow does not necessarily reveal the precise diagnosis of the anatomy of the vascular ring, it does provide enough information to refer the child for surgical division of the ring. Bronchoscopy is a very important diagnostic tool for infants and young children with stridor. Bronchoscopic examination in a child with a vascular ring demonstrates extrinsic (often pulsatile) compression of the trachea. Bronchoscopy is the diagnostic procedure of choice for infants with complete tracheal rings and innominate artery compression syndrome. Echocardiography is very useful for making the diagnosis of pulmonary artery sling. In our current practice, the patient with complete tracheal rings diagnosed by bronchoscopy is evaluated by echocardiography as the diagnostic procedure of choice to rule out pulmonary artery sling. Echocardiography is less useful for the diagnosis of other vascular rings because segments without a lumen cannot be visualized. However, in the context of an esophageal impression after a barium swallow, the general contours of the arch and branches can assist in predicting the precise anatomy. Echocardiography is indicated to rule out a congenital heart lesion in a child with cyanotic episodes. In a child who has a classic vascular ring diagnosed by barium swallow, with no murmur or other cardiac symptoms, echocardiography is not necessary. Computed tomography (CT) and magnetic resonance imaging (MRI) are useful in that they identify both the vascular structures and the tracheo-bronchial anatomy. However, both studies are quite expensive; CT requires the administration of IV contrast material, and MRI requires a significant level of sedation. In our practice, these studies have chiefly been employed if the diagnosis is not clear from the chest x-ray, barium swallow, and bronchoscopy. In patients with either a double aortic arch or a right aortic arch with a left ligamentum, there are four separate bracheocephalic vessels (instead of the normal three) in the superior mediastinum grouped around the trachea. This is called the "four vessel" sign. Angiography is rarely needed for the diagnosis of a vascular ring, but in unusual cases it can offer information not available from any other studies. For example, a 5-month-old infant was admitted recently from an outside hospital with severe CO2 retention (pCO2 = 78mm Hg) despite full ventilator support. A CT scan showed a right aortic arch with the unusual finding of an absent left pulmonary artery. Echocardiography also could not visualize the left pulmonary artery either, so angiography was performed. This demonstrated an absent left pulmonary artery, and compression of the right main bronchus by the combination of a right aortic arch and a right ligamentum. The ligamentum was successfully divided, and the child did well. This illustrates the occasional importance of angiography as the "gold standard" in unusual circumstances. Surgical technique Surgical intervention is indicated in essentially all patients with clinical respiratory symptoms and a diagnosis of a vascular ring. Early and appropriate repair helps avoid serious complications that can occur from hypoxic or apneic episodes. Other reported complications from unrepaired vascular rings include aortic dissection, aortic aneurysm, and catastrophic bleeding from erosion of an indwelling endotracheal tube or NG tube into the ring. Double aortic arch Infants with a double aortic arch typically present quite early in life (newborn to six weeks) and often have severe symptoms with the classic "barky" cough and nearly constant stridor. Most patients can be diagnosed with a chest x-ray and a barium swallow. The surgical approach to a double aortic arch is through a left thoracotomy with a muscle-sparing technique. The pleura overlying the vascular ring should then be opened and careful dissection performed to clearly identify all the pertinent vascular structures. The most common form of double aortic arch is where the right (posterior) arch is dominant (75%). This is illustrated in Figure 3. The left (anterior) arch is dominant in 20% of patients, and the arches are of equal size in 5% of patients. A portion of the smaller arch is atretic in one-third of patients. This area of atresia commonly occurs where the lesser arch inserts into the descending thoracic aorta. An occasional patient has been reported to have a coarctation of both arches!  FIGURE 3. Double aortic arch, right arch dominant. The goal of surgical therapy is to divide the smaller of the two arches at a site that does not compromise the blood flow to the head vessels. Before dividing the arch it should be temporarily occluded and the anesthesiologist asked to check right and left radial and carotid pulses. Arch division should always be done between vascular clamps with oversewing of the divided stumps with prolene suture (Figure 4).   FIGURE 4. [left] Dividing left aortic arch. [right] Arch divided. Simple ligation and division has been associated with ligature slippage and subsequent catastrophic hemorrhage. The divided stumps typically separate by 1.5 to 2 cm, and disappear into the posterior mediastinum making precise hemostasis quite important. This is also the reason that we do not recommend thoracoscopic division of vascular rings using hemoclips.The operative repair is completed by freeing up all adhesive bands surrounding the esophagus in the area of the divided ring. The thoracotomy incision is closed without a chest tube by evacuating air from the plural space with a small suction catheter. The majority of children are extubated in the operating room, monitored in the hospital for 24 to 48 hours, and then discharged home. It may take up to one year for the child's noisy breathing to disappear as the tracheo-bronchomalacia caused by the ring resolves. Right aortic arch Children with a right aortic arch and left ligamentum frequently present somewhat later in life (3 to 9 months of age) because the ring is "looser," being formed partially by the low pressure pulmonary artery and the ligamentum arteriosum. Like patients with a double aortic arch, most patients can be referred for surgery after a chest x-ray and barium swallow. In patients with a right aortic arch, there are two primary branching patterns: 1) retro-esophageal left subclavian artery and 2) mirror image branching. These are illustrated in Figures 5a and b.   FIGURE 5. [left] Right aortic arch, retroesophageal left subclavian artery. [right] Right aortic arch, mirror image branching. Patients with a retro-esophageal left subclavian artery have a vascular ring formed by the right arch, pulmonary artery, and ligamentum. When mirror image branching is present, the ligamentum usually arises anteriorly from the innominate artery, and a ring is not formed. Patients with a right aortic arch and left ligamentum frequently develop an aneurysm at the origin of the left subclavian artery. This is called a Kommerell's diverticulum and is a remnant of the left fourth arch. The surgical approach to a right aortic arch is also through a muscle-sparing left thoracotomy and the fourth intercostal space. The vascular ring is addressed by dividing the ligamentum arteriosum. This is done using two vascular clamps and staged division and oversewing of the stumps of the ligamentum. If there is an associated Kommerell's diverticulum it is either resected and oversewn or (if small) pexed to the fascia of the vertebral column. This prevents compression of the trachea or esophagus from the diverticulum itself. Again, adhesive bands crossing the esophagus are divided. Innominate artery compression syndrome This syndrome can cause stridor, cyanosis, apnea, and respiratory arrest. Frequently, apnea is associated with swallowing a bolus of food. The diagnosis of innominate artery compression syndrome is made by bronchoscopy. Because mild to moderate innominate artery compression can be found in infants who have no respiratory symptoms, we have used a criterion of 75% narrowing before considering patients for surgical intervention. Bronchoscopy demonstrates a right anterolateral compression of the trachea that gives the lumen a classic triangular shape. Lifting the bronchoscope anteriorly against the compression causes obliteration of the right radial, brachial, or temporal pulse. We have treated innominate artery compression syndrome by suspending the innominate artery from the posterior aspect of the sternum through a small right antero-lateral thoracotomy. (Figure 8). Three separate pledgeted sutures are passed through the adventitia of the innominate artery and the posterior table of the sternum. This elevates the anterior tracheal wall and enlarges the tracheal lumen. The child is discharged the following day. It is quite gratifying to eliminate the child's distress with this relatively simple procedure. Pulmonary artery sling A pulmonary artery sling is formed when the left pulmonary artery originates from the right pulmonary artery and encircles the distal trachea, coursing between the trachea and esophagus to reach the hilum of the left lung (Figure 6). The left pulmonary artery then acts as a "sling" that applies pressure on the right main bronchus and right lower trachea. This anomaly was first reported by Glaevecke and Doehle in 1897 as an autopsy finding in a seven-month-old infant who died of severe respiratory distress. Bronchoscopy is performed in all infants diagnosed to have pulmonary artery sling to rule out associated congenital tracheal stenosis with complete tracheal rings. In our experience, 50% of patients with pulmonary artery sling also have complete tracheal rings. This has been referred to as the "ring-sling complex."  FIGURE 6. Pulmonary artery sling. Surgical repair of pulmonary artery sling is undertaken as soon as the diagnosis is made because of the usual tenuous nature of the respiratory status of the child. The mean age at the time of surgery in our series is 4 months.9 Pulmonary artery sling is repaired with a median sternotomy approach and the use of cardiopulmonary bypass. The left pulmonary artery is transected at its origin from the right pulmonary artery and is passed through the mediastinum posterior to the trachea. The left pulmonary artery is then anastomosed to the main pulmonary artery anterior to the trachea as shown in Figure 7. In our series the patency of the left pulmonary artery using a median sternotomy and cardiopulmonary bypass is 100%, with the mean blood flow to the left lung by nuclear scan being 42%.  FIGURE 7. Repaired pulmonary artery sling. Complete tracheal rings Complete tracheal rings occur with congenital absence of the posterior membranous trachea (Figure 8). This is associated with tracheal stenosis that nearly always leads to respiratory distress in infancy. The medical management of this lesion is associated with a 50% mortality rate. Many patients are referred when even the smallest endo-tracheal tube cannot be passed very far below the vocal cords because of the stenosis. The diagnosis is confirmed by rigid bronchoscopy. In many patients the bronchoscope itself cannot be passed, only a fine telescope may be possible. In patients diagnosed with complete tracheal rings, pulmonary artery sling is present in 30% and intracardiac defects in 15%, and these should be ruled out with echocardiography. A total of 38 patients have now undergone repair of complete tracheal rings at Children's Memorial. Twenty-eight have had pericardial tracheoplasty, 2 have had resection with end-to-end anastomosis, 2 have had slide tracheoplasty,10 and 6 have had a new technique developed at Children's—a free tracheal autograft.11  FIGURE 8. Complete trachael rings.  FIGURE 9. Pericardial patch tracheoplasty. The pericardial patch tracheoplasty is performed through a median sternotomy with the use of cardiopulmonary bypass for respiratory support. The trachea is opened anteriorly the entire extent of the stenosis and then patched open with autologous pericardium as shown in Figure 9. The patch is stented with an endotracheal tube for 10–14 days at which time the child is extubated. Bronchoscopy is performed before extubation to remove secretions and granulation tissue and perform dilation if necessary.12 The pericardial patch technique was the first operation successful in the treatment of children with complete tracheal rings. However, a number of patients had prolonged hospitalizations secondary to granulation tissue and scar tissue, and 6 of 28 patients required reoperation and surgical revision.13 Four patients required placement of balloon expandable metallic stents for collapsing tracheal or bronchial segments.  FIGURE 10. The trachea has been opened anteriorly and the autograft resected. In an effort to improve the outcome of these patients, we developed the tracheal autograft technique.11 Using a median sternotomy and cardiopulmonary bypass, the trachea is incised anteriorly throughout the length of the stenosis. Then approximately 6 to 8 tracheal rings or 15–20 mm of trachea are harvested from the mid-portion of the trachea (Figure 10). The trachea is reanastomosed posteriorly and the autograft is used as an anterior patch (Figure 11). In children with a shorter segment of tracheal stenosis, the autograft completes the patch. In patients with a longer stenosis, the autograft has been augmented superiorly with pericardium. This technique has now been successful in 6 consecutive infants. Results and conclusions There has been no operative mortality from an isolated vascular ring or pulmonary artery sling in the Division of Cardiovascular-Thoracic Surgery at Children's Memorial since 1959. The survival rate of infants with complete tracheal rings in our series is 84% with 100% survival using our new tracheal autograft technique. Ninety-two percent of the infants who undergo vascular ring repair are free of respiratory symptoms one year post-operatively. Vascular rings are rare congenital anomalies that cause compression of the trachea and esophagus. Infants present with stridor, barky cough, respiratory distress, cyanosis, and apnea. Diagnosis is best established by barium esophagram for double aortic arch and right aortic arch with left ligamentum. Bronchoscopy is used to diagnose innominate artery compression syndrome and complete tracheal rings. Echocardiogram is the diagnostic procedure of choice for pulmonary artery sling. The surgical approaches to vascular rings include a left thoracotomy for double aortic arch and right aortic arch with ligamentum; right thoracotomy for innominate artery suspension; and median sternotomy with cardiopulmonary bypass for pulmonary artery sling and complete tracheal rings. Close cooperation between the divisions of Cardiovascular-Thoracic Surgery and Otolaryngology have enabled the development of a program with the largest published single institutional experience with vascular rings in North America. REFERENCES 1. Gross RE: Surgical relief for tracheal obstruction from a vascular ring. N Engl J Med 1945;233:586–590. 2. Potts WJ, Holinger PH, Rosenblum AH: Anomalous left pulmonary artery causing obstruction to right main bronchus: report of a case. JAMA 1954;155:1409–11. 3. Idriss FS, DeLeon SY, Ilbawi MN, et al: Tracheoplasty with pericardial patch for extensive tracheal stenosis in infants and children. J Thorac Cardiovasc Surg 1984;88:527–536. 4. Nikaidoh H, Riker WL, Idriss FS: Surgical management of "vascular rings." Arch Surg 1972;105:327–333. 5. Backer CL, Ilbawi MN, Idriss FS, et al: Vascular anomalies causing tracheoesophageal compression. Review of experience in children. J Thorac Cardiovasc Surg 1989;97:725–731. 6. Backer CL, Mavroudis C: Surgical approach to vascular rings. Advances in Cardiac Surgery, Vol 9. (Karp, et al, eds.) St. Louis, MO: Mosby Year-Book, 1997, 29–64. 7. Lowe GM, Donaldson JS, Backer CL: Vascular rings: 10-year review of imaging. RadioGraphics 1991;11:637–646. 8. Backer CL, Holinger LD, Mavroudis C: Innominate artery compression—Division and reimplantation versus suspension [Invited letter and commentary]. J Thorac Cardiovasc Surg 1992;103:817–820. 9. Backer CL, Idriss FS, Holinger LD, et al: Pulmonary artery sling. Results of surgical repair in infancy. J Thorac Cardiovasc Surg 1992;103: 683–691. 10. Dayan SH, Dunham ME, Backer CL, et al: Slide tracheoplasty in the management of congenital tracheal stenosis. Ann Otol Rhinol Laryngol 1997;106:914–919. 11. Backer CL, Mavroudis C, Dunham ME, Holinger LD: Repair of congenital tracheal stenosis with a free tracheal autograft. J Thorac Cardiovasc Surg (In Press, 1998). 12. Dunham ME, Holinger LD, Backer CL, et al: Management of severe congenital tracheal stenosis. Ann Otol Rhinol Laryngol 1994;103:351–356. 13. Backer CL, Mavroudis C, Dunham ME, et al: Reoperation after pericardial patch tracheoplasty. J Pediatr Surg 1997;32:1108–12. |
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