Surgical treatment of a double aortic arch in a dog

Abstract

An 8-month-old spayed female Labrador retriever dog was evaluated for regurgitation 6 months after surgery for a suspected vascular ring anomaly. The dog had a history of regurgitation and slow development as a puppy. An initial left-sided exploratory thoracotomy was unsuccessful in identifying and treating a vascular ring anomaly. The dog was subsequently presented to the PennVet Emergency Service for regurgitation. Thoracic radiography showed cranial thoracic esophageal dilation and an esophageal foreign body that was then removed endoscopically. Subsequent computed tomographic (CT) angiography revealed a double aortic arch. A left 4th intercostal space thoracotomy was performed. The smaller left aortic arch and a left ligamentum arteriosum were ligated and transected. The dog recovered uneventfully and was healthy at the 1-month follow-up visit. This is the 5th reported successful surgical correction of a double aortic arch in a dog. Computed tomographic angiography was essential in diagnosis and surgical planning.

Key clinical message:

Although uncommon, double aortic arches can occur and present a diagnostic and surgical challenge when a persistent right aortic arch is suspected. Computed tomographic angiography provides an accurate preoperative diagnosis and allows for surgical planning.

Vascular ring anomalies are a group of congenital cardiovascular malformations affecting the aortic arch and its branches (1). The vascular ring encircles or compresses the esophagus and causes clinical signs of regurgitation, generally at weaning. The diagnosis is suspected based on the history and radiographic dilation of the esophagus cranial to the heart base (1). Persistence of the right aortic arch with an associated left ligamentum arteriosum is the most common vascular ring anomaly, accounting for 56% of cases (2,3). An accurate anatomical diagnosis of less common (4) vascular ring anomalies, including a left aortic arch with a right ligamentum arteriosum or ductus arteriosus (5), a retroesophageal subclavian artery (1), and double aortic arches (6) is vital to planning both the required surgical approach and procedure. Double aortic arches are uncommon based on the infrequent reports in the veterinary literature. The purpose of this report is to describe the successful clinical investigation and treatment of double aortic arches in a dog that had previously had an unsuccessful exploratory thoracotomy for a suspected vascular ring anomaly.

Case description

An 8-month-old, 22 kg, spayed female Labrador retriever dog was referred to the PennVet Emergency Service for a 6-day history of vomiting or regurgitation and decreased appetite. The dog had a left-sided thoracotomy at 8 wk of age for a suspected persistent right aortic arch (PRAA) after clinical signs of regurgitation prompted a barium study showing dilation of the cranial thoracic esophagus. A left aortic arch was visualized intraoperatively; no vascular ring anomaly was identified, and the surgery was concluded. The dog recovered uneventfully after surgery and was started on a gruel diet in a Bailey chair. The dog had only 1 or 2 isolated instances of regurgitation in the following months. The dog had an episode of regurgitation and suspected aspiration pneumonia 1 wk before presentation to the University of Pennsylvania. Persistent vomiting or regurgitation 5 d later prompted referral.

On presentation the dog was bright, alert, and had normal vital parameters. The dog weighed 21.2 kg. The dog was hypersalivating and the abdomen was tense on palpation. No other abnormalities were noted on physical examination. A focal gastrointestinal ultrasound showed a possible mild reactive mesenteric lymphadenopathy with no foreign material or evidence of mechanical obstruction in the gastrointestinal tract. An abbreviated serum chemistry panel was unremarkable. Thoracic radiographs were taken and revealed a cranial thoracic esophageal dilation containing foreign material. There was a slight leftward and dorsal deviation in the trachea immediately cranial to the heart base. The dog was not coughing and there was no radiographic evidence of pneumonia or other pulmonary disease. Esophagoscopy was performed under general anesthesia and cloth, food, and grass were removed from the esophagus. The dog recovered uneventfully. The radiographic findings were suggestive of a vascular ring anomaly. Due to the findings of the previous thoracotomy, differentials including an atypical vascular ring anomaly and a congenital esophageal stricture or stenosis were considered.

A complete blood (cell) count and serum chemistry were performed revealing a mild anemia [hematocrit 39.9%; reference range (RR): 41.0 to 58.0%] and hypoglycemia (glucose 51 mg/dL; RR: 65.0 to 112 mg/dL). The dog was blood typed as DEA 1.1 negative. The dog was anesthetized but the planned computed tomographic (CT) scan was unsuccessful due to a CT generator malfunction. The dog recovered and was discharged.

The dog was readmitted 2 wk later for CT angiography and surgery. The dog weighed 22 kg and no abnormalities were detected on physical examination. The dog was premedicated with butorphanol (Zoetis, Kalamazoo, Michigan, USA), 0.2 mg/kg body weight (BW), IM. Anesthesia was induced with propofol (Fresenius Kali, Lake Zurich, Illinois, USA) 2.5 mg/kg BW, IV and maintained with sevoflurane (Piramal Critical Care, Bethlehem, Pennsylvania, USA) in oxygen during the CT scan. A sterile iodinated contrast agent (2.2 mg/kg BW) was injected intravenously to provide radiographic contrast. Computed tomographic angiography confirmed the presence of the double aortic arch creating a vascular ring and allowed further characterization of the vascular anomalies. The common carotid arteries were the first branches arising from the aortic root, with the right slightly dorsal to the left. There was no brachiocephalic trunk present. The aorta then bifurcated into 2 aortic arches, with the right subclavian artery arising from the right aortic arch and the left subclavian and left aortic arch arising together from the aortic root then immediately separating (Figure 1). The right aortic arch was much larger (~50%) than the left and ran dorsally along midline to the right of the esophagus and trachea. The smaller left arch extended to the left of midline and wrapped dorsally around the left side of the esophagus and trachea. The 2 aortic arches rejoined slightly left of midline and dorsal to the trachea and esophagus creating a complete vascular ring around the esophagus and trachea (Figures 1, 2A–D). The descending aorta then continued caudally on the left side. A dilation consistent with a ductus diverticulum was present on the ventral wall of the left aorta. The trachea was displaced to the left and was slightly narrowed at the level of the vascular ring. The cranial thoracic esophagus was positioned to the left of the trachea, was enlarged, and contained a large volume of gas and hypoattenuating material. The esophagus was compressed at the level of the vascular ring and was gas-filled caudal to it. A band of soft tissue extending from the left thoracic wall to the mediastinum, consistent with adhesions due to the previous thoracotomy, displaced the left cranial lung lobe caudally. This lung lobe was scalloped on the dorsal margins.

Figure 1.

Three-dimensional contrast computed tomography reconstruction showing the right (RAA) and left (LAA) aortic arches, the right (*) and left (**) carotid arteries, and the right (#) and left (##) subclavian arteries.

Figure 2A–D.

Sequential transverse contrast CT images showing right (red arrow) and left (yellow arrow) aortic arches encircling the trachea and esophagus. T — Trachea; E — Esophagus.

The dog was prepared for aseptic surgery. Additional propofol, 4.5 mg/kg BW, IV was administered and the dog was transitioned to inhalant isoflurane in oxygen to maintain anesthesia. Constant rate infusions of lidocaine (APP Pharmaceuticals, Schaumburg. Illinois, USA), 50 μg/kg BW per minute and fentanyl (Hospira, Lake Forest, Illinois, USA), 50 μg/kg BW per minute were initiated. A morphine (West-Ward Pharmaceutical, Eatontown, New Jersey, USA), 0.1 mg/kg BW intercostal block was conducted and peri- and intraoperative doses of cefazolin, 22 mg/kg BW, IV were administered every 90 min. The dog was maintained on mechanical ventilation throughout the thoracotomy.

A left 4th intercostal space thoracotomy was performed. There were significant adhesions between the thoracic wall, mediastinum, and left cranial lung lobe at the site of prior thoracotomy which were dissected. Self-retaining retractors were used to maintain exposure of the surgical site. The mediastinum was further dissected and the left ligamentum arteriosum was palpable overlying the esophagus. The ligamentum was isolated, ligated on either side with 3/0 polydioxanone suture (PDS), and transected. The left aortic arch was identified, dissected, clamped with ductus clamps and transected (Figure 3). Several attempts were made to oversew the ends with 4/0 prolene using a C1 needle, but the aortic tissue was too friable. Each side of the left arch was double ligated with encircling ligatures of O silk. During thoracotomy closure, air leakage from an adhesion site in the left cranial lung lobe was appreciated. A lobectomy was performed using a surgical stapler and a 30-mm cartridge. A chest tube was placed, and the thoracotomy closed routinely.

Figure 3.

The left aortic arch dissected from the mediastinum.

The dog made an uneventful recovery from surgery. The chest tube was removed 24 h after surgery and the dog was discharged 3 d later. The dog was re-evaluated 1 mo after surgery and was eating in a normal position with no regurgitation. Four years after surgery, the dog is a normal size and weight (34 kg) and is eating normally.

Discussion

This case highlights the importance of advanced imaging in planning surgery to treat a vascular ring anomaly. Computed tomography angiography was vital in confirming the suspicion of a double aortic arch and determining the dominant aortic arch. Typically, history, clinical signs, and cranial thoracic esophageal dilation seen on plain thoracic radiographs and during a barium esophagram raise suspicion for a vascular ring anomaly. Leftward deviation of the trachea at the cranial aspect of the cardiac silhouette on dorsoventral or ventrodorsal thoracic radiographs indicates the likely presence of a right aortic arch (3). These diagnostics can provide adequate evidence for surgical exploration. However, the surgeon is at a disadvantage if the dog has a different type of vascular ring anomaly that requires more exploratory dissection. Both angiography and CT angiography have been used to preoperatively determine the nature of canine vascular ring anomalies (7,8).

In the embryo, paired dorsal, and ventral aortas are joined by 6 pairs of arches that surround the embryonic foregut (9–11). The arches involute or develop to produce the aorta and its major initial branches. Vascular rings occur because of abnormal embryonal development of the aortic arches which can entrap the esophagus, resulting in clinical signs of regurgitation at weaning (9–11). In dogs, most vascular ring anomalies involve a persistence of the right 4th aortic arch as the ascending aorta and the left 6th arch as the ligamentum arteriosum (9–11). However, as this case demonstrates, other types of vascular rings occur in dogs. This dog had an initial exploratory thoracotomy for a suspected vascular ring anomaly that was ended when a left aortic arch was visualized.

Understanding the anatomy of the vascular ring is vital in planning and performing surgery to correct the anomalies. Double aortic arches are uncommon but occur when the left and right 4th aortic arches persist concurrently. This is classified as a Type 4 vascular ring anomaly (11). Double aortic arches have been described in humans (12), dogs (6,13–19), a monkey (20), a cat (21), and a lion (22). Double aortic arches can be further classified as right arch dominant, left arch dominant and symmetrical arches (12). All 3 types have been reported in dogs (6,13–19). The right arch dominant, as seen in this case, is the most common, although most diagnoses in veterinary medicine have been made at post-mortem (6). In this case the tentative diagnosis of a vascular ring anomaly was made when the dog was several months old and it was referred to a specialist for surgery. Advanced imaging was not performed, however, and the complex nature of vascular ring anomaly was not recognized before the initial surgery.

This case is the 5th reported successful surgical correction of a double aortic arch in a dog that has survived to be discharged from the hospital (6,13,17,18). This is the 2nd reported case in which advanced imaging was performed before surgery to correct a double aortic arch. Both animals had an excellent outcome despite the historically poor prognosis for a surgical treatment of double aortic arches (13). We attributed this to CT imaging of the vascular anatomy before surgery that facilitated precise surgical planning. In this case, CT angiography was useful in assessing the diameters of both aortic arches and the decision to ligate and divide the smaller left arch. Ligation of the dominant aortic arch can lead to hypertension and increased cardiac after-load (12). In cases in which both arches are of similar size, each arch is separately isolated and temporarily occluded, as systemic blood pressure is measured to determine if 1 arch can be safely ligated and divided (16). Although surgery to correct vascular rings can correct esophageal constriction, esophageal dilation and motility have variable degrees of resolution after surgery and long-term medical management may be necessary (23). The degree of preoperative esophageal dilation may not necessarily correspond to the dog’s ability to swallow postoperatively. The dog in this report was able to eat in a normal position without regurgitation soon after surgery and was clinically normal 4 y later. CVJ