37 Eric Monnet Persistent right aortic arch (PRAA) with left ligamentum arteriosum accounts for greater than 90% of vascular ring anomalies in dogs.1 In addition There are five other types of vascular anomalies that can compromise the lumen of the esophagus (Figures 37.1).2,3 Currently, only the persistence of a right aortic arch with a left ligamentum arteriosum has been successfully treated with thoracoscopy.4,5 German shepherds, Irish setters, and Boston terriers are thought to be at increased risk for development of a vascular ring anomaly.3,6,7 This condition is usually diagnosed in young dogs when they are transitioned from a liquid to a solid food, and this surgery is therefore performed in animals of a small size. Pediatric instruments and telescope may be required for an appropriately sized instrumentation in the thoracic cavity. Figure 37.1 Normal anatomy. Left aortic arch (LAA) with the brachiocephalic trunk (BCT) and left subclavian artery (LS). The right subclavian artery (RS) branches off the brachiocephalic trunk. The esophagus is located to the right of the aortic arch. (Courtesy of Boel A. Fransson, Washington State University, Pullman, WA.) Several different types of vascular ring anomalies have been described in the literature in dogs and cats.2,3 All the vascular ring anomalies except the double aortic arch (see Figure 37.2F) are likely treatable by video-assisted thoracoscopic surgery (VATS). Only the correction of esophageal compression by a ligamentum arteriosum associated to a PRAA (see Figure 37.2A) has been reported in the literature.4,5 Figure 37.2 A, Persistent right aortic arch (RAA). The ligamentum arteriosum (LA) extends between the left pulmonary artery and the anomalous RAA, causing constriction of the esophagus by the vascular ring. B, Same as part A, but in addition, an aberrant left subclavian (LS) artery arises from the persistent RAA and compresses the esophagus on its dorsal aspect as the artery traverses from right to left in the cranial mediastinum. The esophagus is dually compressed by a complete vascular ring (persistent RAA with left LA) and by a partial vascular ring (aberrant LS artery). C, Similar to part B, with one important exception: the LA is traversing ventral to the esophagus and does not add to constriction of the esophagus; this is an example of a partial vascular ring anomaly. D, An example of vascular ring anomaly with a left aortic arch (LAA): persistent right ligamentum arteriosus (RLA, ductus; RDA), essentially the mirror image of persistent RAA in part A. The RLA or RDA arises from the pulmonary artery and extends to the aortic arch, compressing the esophagus on its right side. E, Aberrant right subclavian artery (RSA): the RSA arises from the normal LAA rather than from the brachiocephalic trunk (BCT), thus compressing the esophagus on its dorsal aspect as the artery traverses to the right side. F, Double aortic arch (DAA): both the left and the right fourth arches persist and are functional. This type of anomaly may also result in respiratory signs secondary to constriction of the trachea along with the esophagus. (Courtesy of Boel A. Fransson, Washington State University, Pullman, WA.) Surgery to relieve esophageal obstruction associated with vascular ring anomaly should be considered palliative and not curative in most cases.1,6,7 Esophageal diameter and motility rarely become completely normal after surgery.3,6 Continued medical management with semiliquid diets and upright feeding may be necessary for a long period or indefinitely after surgical correction.6 Prognostic indicators for vascular ring anomaly in small animals have not been identified.7 Severe dilation of the cranial esophagus is considered to be indicative of a guarded prognosis. Dilation and hypomotility of the esophagus caudal to the vascular ring anomaly suggests that vagal nerve injury has occurred and dictates a more guarded prognosis.3 The timing of surgical intervention may be an important prognostic consideration. Generally, the sooner surgical intervention is undertaken, the less the degree of permanent esophageal injury. Aspiration pneumonia and severe nutritional debilitation also must be considered in the timing of surgery.3 Surgery may have to be delayed in favor of nutritional supportive care with liquid diets or tube gastrostomy in some cases. Ligamentum arteriosum containing a patent ductus with blood flow could represent a challenge under thoracoscopy. Patent ductus arteriosus have been treated by VATS.8 Those dogs had an otherwise normal vascular anatomy. Dissection of a patent ductus arteriosus may be more challenging in dogs with a PRAA. If blood flow is present in the ligamentum arteriosum, a continuous murmur should theoretically be present. Patients with an aberrant right subclavian artery (see Figure 37.2E) might represent a contraindication for VATS because this anomaly can be difficult to localize, dissect, and ligate. Clinical findings associated with vascular ring anomaly are related to esophageal obstruction. Postprandial regurgitation usually manifests some time after weaning when animals start to receive solid food.3 Affected animals are often small compared with their littermates despite a ravenous appetite. Bulging of the cervical esophagus may be seen upon gentle compression of the thorax or abdomen, especially after a meal. Regurgitation may result in aspiration pneumonia that will cause significant respiratory distress. Concurrent tracheal entrapment may cause signs of fixed airway obstruction if a rare double aortic arch is present. Signs related to cardiac abnormalities usually are not identified. Esophageal dilation cranial to the base of the heart on plain thoracic radiographs or barium esophagram (Figure 37.5) suggests the presence of a vascular ring anomaly (Figure 37.2).2,9
Thoracoscopic Treatment of Vascular Ring Anomalies
Preoperative Considerations
Patient Selection
Diagnosis and Imaging
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