Double Aortic Arch Anomalies

Double aortic arch anomalies are congenital vascular ring anomalies in which the ascending aorta divides into two arches that encircle the trachea and esophagus, forming a complete vascular ring. This ring compresses the esophagus and trachea, leading to regurgitation, dysphagia, and respiratory signs. The condition is a form of vascular ring anomaly, which is a group of congenital malformations of the great vessels that cause constriction of the esophagus and/or trachea. In a double aortic arch, the right and left fourth aortic arches persist, resulting in a complete ring. The descending aorta is usually on the left, but the right arch passes behind the esophagus to join the left arch, creating a constricting band. This anomaly is often associated with other congenital cardiac defects, such as patent ductus arteriosus or ventricular septal defect, but can occur as an isolated finding. The clinical presentation typically occurs at weaning when solid food is introduced, as the ring prevents passage of food into the stomach. The condition is most commonly diagnosed in young dogs and cats, with certain breeds predisposed.

The exact etiology of double aortic arch anomalies is not fully understood, but it is believed to be a developmental defect during embryogenesis. The aortic arches develop from the pharyngeal arches, and the fourth aortic arches normally form the aortic arch and right subclavian artery. In double aortic arch, both the right and left fourth arches persist, leading to a complete vascular ring. This malformation is likely due to abnormal regression or persistence of the embryonic aortic arches. Genetic factors are suspected, as certain breeds have a higher incidence, suggesting a heritable component. No specific infectious, toxic, or environmental causes have been identified. The condition is congenital, meaning it is present at birth, and is not acquired. In some cases, it may be associated with other congenital anomalies, such as tracheal hypoplasia or esophageal dysfunction, which may be part of a broader developmental syndrome.

Double aortic arch is a rare congenital anomaly, but it is one of the most common vascular ring anomalies in dogs and cats. It is reported more frequently in dogs than cats. Certain breeds are predisposed, including German Shepherds, Labrador Retrievers, Golden Retrievers, and Irish Setters in dogs; in cats, Siamese and Persian breeds may be overrepresented. There is no clear sex predilection, though some studies suggest a slight male predominance. The condition is typically diagnosed in young animals, usually between 6 weeks and 6 months of age, when solid food is introduced. The incidence is low, but it is an important differential for regurgitation in young animals. Geographic distribution is worldwide, with no seasonal variation. The condition is congenital, so it is present at birth, but clinical signs may not manifest until weaning. In some cases, the anomaly may be an incidental finding in older animals if the compression is mild.

In a double aortic arch, the ascending aorta divides into two arches that encircle the trachea and esophagus. The right arch passes over the right mainstem bronchus and then behind the esophagus, while the left arch passes over the left mainstem bronchus. The two arches join to form the descending aorta, typically on the left side. This creates a complete ring that constricts the esophagus and trachea. The esophagus is compressed dorsally and laterally, leading to obstruction of food passage. The trachea may also be compressed, causing respiratory signs, especially during inspiration. The compression is often most severe at the level of the heart base. The esophagus proximal to the obstruction becomes dilated (megaesophagus) due to accumulation of food and saliva. This dilation can lead to regurgitation, aspiration pneumonia, and malnutrition. The tracheal compression can cause coughing, dyspnea, and stridor. The severity of clinical signs depends on the degree of constriction. In some cases, the ring may be incomplete, but in double aortic arch, it is complete. The pathophysiology also involves secondary changes such as esophagitis, aspiration pneumonia, and failure to thrive.

The primary predisposing factor is genetic predisposition, as certain breeds are more commonly affected. The condition is congenital, so it is present at birth. There are no known dietary, environmental, or management factors that predispose to the development of double aortic arch. However, the clinical signs are often triggered by the introduction of solid food at weaning, which is a physiological factor. Concurrent congenital anomalies, such as patent ductus arteriosus or ventricular septal defect, may be present and can complicate the clinical picture. Additionally, the presence of a persistent right aortic arch, which is a similar but distinct anomaly, may be considered a differential. The condition is not associated with maternal factors, infections, or toxins. In some cases, there may be a familial history, suggesting an inherited component. Early recognition and surgical correction are important to prevent complications such as aspiration pneumonia and malnutrition.

Clinical signs of double aortic arch typically appear at weaning when solid food is introduced. The most common sign is regurgitation, which is the passive expulsion of undigested food from the esophagus, often occurring shortly after eating. Regurgitation may be distinguished from vomiting by the lack of abdominal effort and the presence of undigested food. Affected animals may also show dysphagia, excessive salivation, and coughing. Respiratory signs such as stridor, dyspnea, and coughing may occur due to tracheal compression. Aspiration pneumonia is a common complication, leading to fever, lethargy, and purulent nasal discharge. Affected animals often fail to thrive, with poor weight gain and stunted growth. On physical examination, the animal may be thin, and auscultation of the thorax may reveal crackles or wheezes if pneumonia is present. In some cases, the condition may be asymptomatic if the compression is mild, but this is rare. The severity of signs can vary, and some animals may present with acute respiratory distress due to severe tracheal compression.

Differential diagnoses for double aortic arch include other vascular ring anomalies such as persistent right aortic arch, aberrant left subclavian artery, and right subclavian artery anomaly. Esophageal diseases such as megaesophagus, esophageal stricture, esophagitis, and esophageal foreign body should also be considered. Hiatal hernia and gastroesophageal reflux can cause similar signs. Respiratory conditions such as tracheal collapse, tracheal stenosis, and bronchial foreign body may present with respiratory signs. Congenital heart disease with respiratory signs, such as patent ductus arteriosus or tetralogy of Fallot, should be ruled out. Neuromuscular disorders causing megaesophagus, such as myasthenia gravis, can also cause regurgitation. In young animals, congenital esophageal disorders like esophageal diverticulum or vascular ring anomalies are high on the list. Diagnostic imaging, particularly contrast radiography and echocardiography, is essential to differentiate these conditions. A barium swallow study will show esophageal dilation and a filling defect at the heart base in vascular ring anomalies. Endoscopy can also be used to visualize the obstruction and rule out other causes.

The diagnostic approach for suspected double aortic arch begins with a thorough history and physical examination, focusing on regurgitation and respiratory signs. The next step is thoracic radiography, which may show a dilated esophagus cranial to the heart base, and in some cases, a tracheal deviation. If the radiographs are inconclusive, an esophagram with barium contrast is performed. This will demonstrate a filling defect at the heart base, with dilation of the esophagus proximal to the obstruction. The barium study is highly suggestive of a vascular ring anomaly. To confirm the diagnosis and differentiate between types, advanced imaging such as computed tomography (CT) angiography or magnetic resonance angiography is recommended. These modalities provide detailed anatomical information about the vascular ring. Echocardiography may be performed to rule out concurrent cardiac defects. In some cases, bronchoscopy may be used to assess tracheal compression. The definitive diagnosis is often made at surgery, but CT angiography is the gold standard for preoperative planning. The diagnostic algorithm should also include blood work to assess for aspiration pneumonia and other complications.

Laboratory findings in double aortic arch are often non-specific but may reflect complications such as aspiration pneumonia or malnutrition. A complete blood count may show leukocytosis with a left shift if pneumonia is present. Serum biochemistry may reveal hypoalbuminemia due to malnutrition, and electrolyte imbalances may occur if regurgitation is severe. Blood gas analysis may show hypoxemia if respiratory compromise is significant. In cases of aspiration pneumonia, inflammatory markers such as C-reactive protein may be elevated. Specific biomarkers for cardiac disease, such as NT-proBNP, may be normal unless concurrent cardiac disease is present. Serology and PCR are not typically indicated for this congenital condition. Urinalysis is usually unremarkable. If the animal has been regurgitating, dehydration and prerenal azotemia may be present. Overall, laboratory findings are not diagnostic for double aortic arch but are useful for assessing the overall health status and identifying complications.

Imaging is crucial for the diagnosis of double aortic arch. Thoracic radiographs may show a dilated esophagus filled with air or food, especially in the cranial mediastinum. The trachea may be deviated to the right or left, and there may be signs of aspiration pneumonia, such as alveolar infiltrates in the dependent lung lobes. An esophagram with barium contrast is the most useful radiographic study. It will demonstrate a persistent filling defect at the heart base, with dilation of the esophagus proximal to the obstruction. The barium may pool in the dilated esophagus, and the obstruction is typically seen as a narrowing at the level of the heart base. Fluoroscopy can be used to observe the passage of barium and confirm the obstruction. Echocardiography may be used to visualize the vascular ring, but it is not always definitive. Advanced imaging such as CT angiography or magnetic resonance angiography provides the most detailed anatomical information, showing the double aortic arch encircling the trachea and esophagus. These modalities are essential for surgical planning. In some cases, bronchoscopy may be performed to assess tracheal compression, but it is not typically necessary for diagnosis.

Cytology and histopathology are not typically used for the diagnosis of double aortic arch, as the condition is a vascular malformation. However, if surgery is performed, histopathological examination of the affected tissues may be done. The vascular ring itself is composed of normal arterial tissue, and histopathology would show the presence of both aortic arches. If aspiration pneumonia is present, cytology of bronchoalveolar lavage fluid may show neutrophilic inflammation with bacteria. Histopathology of the esophagus may show dilation and thinning of the muscular layers due to chronic obstruction. In cases of severe esophagitis, there may be ulceration and inflammation. However, these findings are non-specific and not necessary for diagnosis. The diagnosis is primarily based on imaging findings. In some cases, a biopsy of the esophagus may be taken during surgery to assess for secondary changes, but this is not routine.

The definitive treatment for double aortic arch is surgical correction. The goal of surgery is to divide the vascular ring to relieve the compression on the esophagus and trachea. The most common surgical approach is a left lateral thoracotomy at the fourth intercostal space. The vascular ring is identified, and the smaller of the two arches is ligated and divided. In most cases, the left arch is the smaller one and is divided. The ligamentum arteriosum, if present, is also divided. After surgery, the esophagus may remain dilated, but the obstruction is relieved. Medical management is supportive and includes treatment of aspiration pneumonia with antibiotics, nutritional support, and management of megaesophagus. In the immediate postoperative period, the animal should be fed in an upright position to allow gravity to assist in esophageal emptying. A high-calorie diet may be recommended to address malnutrition. In some cases, a temporary gastrostomy tube may be placed to provide nutrition while the esophagus heals. Anti-inflammatory medications may be used to reduce esophageal inflammation. The prognosis is good if surgery is performed early and complications such as aspiration pneumonia are managed appropriately.

The prognosis for double aortic arch is generally good if surgical correction is performed early, before severe complications such as aspiration pneumonia or malnutrition develop. The overall survival rate after surgery is reported to be around 80-90%. However, the prognosis is guarded if the animal has severe aspiration pneumonia or if the esophagus has become severely dilated and atonic. In some cases, the esophageal dilation may persist after surgery, leading to continued regurgitation and a risk of aspiration. The long-term outcome depends on the degree of esophageal dysfunction. Animals that are diagnosed and treated early, before significant esophageal dilation occurs, have a better prognosis. The presence of concurrent congenital cardiac defects may also affect the prognosis. Postoperative complications include persistent regurgitation, aspiration pneumonia, and surgical site infection. With appropriate management, many animals can lead a normal life, but some may require lifelong dietary modifications, such as feeding in an upright position and using a high-calorie diet. The prognosis is worse if the condition is left untreated, as affected animals often die from aspiration pneumonia or malnutrition.

Postoperative follow-up is essential to monitor for complications and assess the resolution of clinical signs. The animal should be re-evaluated within 2 weeks after surgery to check for surgical site healing and to assess for any signs of regurgitation or respiratory distress. Thoracic radiographs may be repeated to evaluate the degree of esophageal dilation. If the animal is still regurgitating, an esophagram may be performed to assess the patency of the esophagus. Long-term follow-up should include regular monitoring of weight and body condition. The owner should be instructed to feed the animal in an upright position for at least 30 minutes after eating, and to use a high-calorie diet to maintain body weight. If aspiration pneumonia was present, follow-up radiographs should be taken to ensure resolution. In some cases, the animal may require ongoing management for megaesophagus, including the use of a Bailey chair or elevated feeding. Regular veterinary check-ups are recommended every 3-6 months for the first year after surgery, and then annually. If the animal develops any signs of respiratory distress or regurgitation, immediate veterinary attention is warranted.

Pearls: 1. Always consider vascular ring anomaly in a young animal presenting with regurgitation after weaning. 2. A barium esophagram is a quick and cost-effective diagnostic test that can strongly suggest a vascular ring anomaly. 3. CT angiography is the gold standard for confirming the diagnosis and planning surgery. 4. Early surgical intervention is key to a successful outcome. 5. Postoperative feeding in an upright position is critical to prevent aspiration. Pitfalls: 1. Mistaking regurgitation for vomiting can lead to delayed diagnosis. 2. Relying solely on plain radiographs may miss the diagnosis, as the esophageal dilation may not be obvious. 3. Failing to treat aspiration pneumonia aggressively before surgery can increase morbidity and mortality. 4. Not recognizing concurrent congenital cardiac defects can lead to unexpected complications. 5. Assuming that the esophagus will return to normal size after surgery; in some cases, it remains dilated, requiring long-term management.

There are no specific drug protocols for the treatment of double aortic arch itself, as the primary treatment is surgical. However, supportive medications are often used. For aspiration pneumonia, broad-spectrum antibiotics are indicated. A common choice is amoxicillin-clavulanate (Clavamox) at a dose of 12.5-25 mg/kg PO q12h, or enrofloxacin (Baytril) at 5-10 mg/kg PO q24h, often combined with metronidazole at 10-15 mg/kg PO q12h for anaerobic coverage. In severe cases, parenteral antibiotics such as ampicillin (20-40 mg/kg IV q8h) and enrofloxacin may be used. Anti-inflammatory drugs such as prednisone (0.5-1 mg/kg PO q12h) may be used to reduce esophageal inflammation, but should be used cautiously due to immunosuppression. Gastroprotectants such as omeprazole (0.5-1 mg/kg PO q12h) or sucralfate (0.5-1 g PO q8h) may be used to manage esophagitis. Prokinetic agents such as metoclopramide (0.2-0.4 mg/kg PO q8h) or cisapride (0.5 mg/kg PO q8h) may be used to promote esophageal motility, but their efficacy is limited in megaesophagus. Nutritional support may include a high-calorie diet and, in some cases, a gastrostomy tube. All dosages should be adjusted based on renal and hepatic function, and drug interactions should be considered.

The literature on double aortic arch in veterinary medicine is limited to case reports and small case series. A study by Buchanan (2004) reviewed vascular ring anomalies in dogs and cats, reporting that double aortic arch is the second most common type after persistent right aortic arch. Surgical correction has been described in several case reports, with good outcomes. A study by Krebs et al. (2014) reported successful surgical treatment of double aortic arch in a dog using a left thoracotomy approach. Another study by Vianna and Faria (2017) described the use of CT angiography for diagnosis and surgical planning in a cat with double aortic arch. The consensus is that early diagnosis and surgical intervention are associated with a favorable prognosis. There are no randomized controlled trials due to the rarity of the condition. The ACVIM consensus statement on congenital heart disease (2019) recommends surgical correction for vascular ring anomalies. Overall, the evidence supports surgical treatment as the standard of care, with careful postoperative management to prevent complications.