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Vascular ring anomalies in the dog and cat

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Category: Schede
Hits: 10
  • Disciplina: Gastroenterologia
  • Specie: Cane e Gatto

Vascular ring anomalies are congenital malformations of the great vessels and their branches which  entrap the oesophagus (and trachea) causing their obstruction. Persistent right aortic arch (PRAA) is the most common anomaly and accounts for about 90% of these disorders. Other anomalies that have been reported are right persistent ductus arteriosus, aberrant right or left subclavian artery (the second most common anomaly), double aortic arch, persistent right dorsal aorta, aberrant intercostal arteries, left subclavian artery and brachiocephalic arteries (reported in the English Bulldog). More than one anomaly can be present in the same patient, although this occurs only sporadically.5 Vascular ring anomalies are less common in the cat than in the dog, but PRAA is the most frequent anomaly in both species.

 

AETIOLOGY

Vascular ring anomalies are congenital disorders in which there is an abnormal development of the embryonic aortic arches; this causes the formation of a fibrous ring that compresses the oesophagus, altering its motility and function. A family tendency has been reported in the German Shepherd dog, the Irish Setter and English Bulldog. No breed predisposition has been noted in the cat. More than one puppy of the same litter can be affected by vascular ring anomalies. In animals with PRAA, the oesophagus remains trapped between the aorta on the right, the pulmonary trunk on the left, the ligamentum arteriosum dorso-laterally and the base of the heart ventrally (Fig. 1). This compression causes progressive dilatation of the oesophagus cranial to the obstruction (Fig. 2).

 

CLINICAL SIGNS

The clinical signs typically appear at the time the affected animal is weaned. The ingestion of semisolid and/or solid food is followed by regurgitation; in the early stages this occurs immediately after intake of the food, whereas with progressive dilatation of the oesophagus, the regurgitation can occur some time after the meal. Affected subjects typically appear debilitated and smaller than their littermates. They can also show altered appetite and anorexia when oesophagitis is present. If aspiration pneumonia occurs following regurgitation, the patient develops a cough, dyspnoea and fever. In some animals in which the compression caused by the vascular ring anomaly is not completely obstructive the clinical signs may be less clear and persistent and the affected subjects may grow almost normally. In such patients the regurgitation may worsen and become persistent as the oesophageal dilatation progresses.

 

DIAGNOSIS

 

The diagnosis is suspected on the basis of the history and clinical signs, but is confirmed by plain X-rays (Fig. 3) and contrast radiography. The plain X-rays show oesophageal dilatation and the presence of food and air cranially to the heart; the normal radio-opacity of the aortic arch is usually absent. Furthermore, there may be narrowing of the lumen and ventral displacement of the trachea. In a recent study1 it was found that, among 27 cases of PRAA for which ventro-dorsal and/or dorso-ventral X-rays were available, all 27 had a focal, leftward deviation of the trachea at the cranial border of the heart. Contrast radiography shows interruption of the passage of barium at the level of the base of the heart (Figs. 3a, 4, 5 and 5a) and variable degrees of dilatation proximal to the obstruction. In some cases there may also be moderate dilatation of the thoracic oesophagus. Fluoroscopy may also reveal loss of motility of the proximal oesophagus.

 

 

The main radiographic differential diagnosis of vascular ring anomaly is oesophageal stenosis in the case that this is localised to the thoracic aorta dorsal to the heart. Angiography can demonstrate the vascular abnormality and sometimes define it better in view of surgical correction. An endoscopic examination is not indispensable for the diagnosis and does not help to differentiate the abnormalities. Oesophagoscopy (Fig. 6) can be used in doubtful cases to confirm a suspected diagnosis; furthermore, this examination can detect and evaluate any oesophagitis associated with PRAA and, if necessary, be used to remove any foreign bodies blocked cranially to the obstruction.

 

TREATMENT

Once the vascular ring anomaly has been diagnosed, surgical correction should be performed as soon as possible. The affected patients are often debilitated and malnourished; in these cases the animals must be given adequate nutrition and be hydrated and stabilised prior to surgery. With this aim the animals can be fed frequently with small, semi-liquid meals keeping the food to be eaten at a height or the patient in a vertical position. When this food management does not have the desired effects and the patient continues to regurgitate, it is advisable to bypass the oesophageal stricture. This can be done by placing a naso-gastric tube blindly or under endoscopic vision. Blind introduction of such a tube is difficult when the pre-stenotic dilatation is large and/or the stenosis severe. Alternatively, a gastric tube (by percutaneous endoscopic gastrotomy) can be placed, although this requires surgery.

If there are clinical signs of aspiration pneumonia, the patient must be treated with antibiotics prior to surgery. The surgical correction should be carried out as soon as the patient is considered able to tolerate it from an anaesthesiological point of view. Besides a competent surgeon, proper anaesthetic management is fundamental because the animal, which is usually small, requires a thoracotomy. A corrective technique that can be carried out via thoracoscopy has, however, recently been reported.2 In some patients, oesophageal dysfunction together with a variable degree of dilatation persist despite the surgical correction. Furthermore, some patients also have dilatation of the portion of the oesophagus distal to the stenosis, presumably as a result of a neuromuscular dysfunction. Most patients have a clear improvement after surgical correction. In a retrospective study of 25 dogs treated surgically, 23 had a good clinical outcome with only sporadic regurgitation. In the case that symptoms persist after the corrective surgery, the same dietary measures as those used in megaoesophagus can be implemented.

There are no firmly established prognostic factors in vascular ring anomalies, although a study by Rallis,3 published in 2000, indicated that marked dilatation of the pre-stenotic oesophagus is a negative prognostic factor. In the opinion of the author, the success of the intervention is fundamentally dependent on the animal being in a good clinical condition prior to the operation, as well as on the skill and experience of the surgeon and anaesthetist.

 

References

  1. Buchanan JW. Tracheal signs and associated vascular anomalies in dogs with persistent right aortic arch.J Vet Intern Med. 2004 Jul-Aug;18(4):510-4.
  2. MacPhail CM, Monnet E, Twedt DC. Thoracoscopic correction of persistent right aortic arch in a dog.J Am Anim Hosp Assoc. 2001 Nov-Dec;37(6):577-81
  3. Rallis T et al.: Persistent right aortic arch: does the degree of esophageal dilatation affect long-term outcome? A retrospective study in 10 dogs and 4 cats, Eur J Compar Gastroent 5(1):29, 2000.
  4. Muldoon MM, Birchard SJ, Ellison GW.Long-term results of surgical correction of persistent right aortic arch in dogs: 25 cases (1980-1995).J Am Vet Med Assoc. 1997 Jun 15;210(12):1761-3
  5. LoughinCA, Marino DJ. Delayed primary surgical treatment in a dog with a persistent right aortic arch.J Am Anim Hosp Assoc. 2008 Sep-Oct;44(5):258-61