Right sided aortic arch in children with persistent respiratory symptoms

Case reports

Case 1— A 12 year old boy complained of shortness of breath on exercise, worsening over a year, with no other symptoms. Examination was normal. Bronchodilators and inhaled steroids had not helped. Previous investigations included chest radiography, computed tomography of the chest, echocardiography, exercise testing, full lung function tests, measurement of immunoglobulin concentrations, and skin prick testing for allergies. Interstitial lung disease had been suggested on the basis of reduced total lung capacity and residual volume. Review of the original chest x ray film, six months after his initial presentation, showed a right sided aortic arch, with tracheal compression. Repeat spirometry yielded reduced inspiratory and expiratory flow rates, with flattened inspiratory and expiratory flow volume loops. A second echocardiogram along with angiography confirmed a right sided aortic arch with an aberrant left subclavian artery. Bronchoscopy showed narrowing of the distal trachea and right main bronchus. The patient underwent surgery. Constriction of the airway was caused by a ligamentum arteriosum, arising from the first part of the descending thoracic aorta and attached to the left pulmonary artery. The ligamentum was divided. After surgery, symptoms and lung function improved (forced expiratory volume in one second increased from 82% to 106% predicted).

Case 2— A 12 year old boy was referred with asthma, which was insensitive to steroids. He complained of tightness of the chest and cough, which were worse with exercise, colds, and changes in the weather. Bronchodilators occasionally helped. He also had eczema. Four first degree relatives were atopic. Peak flow was reduced but steady between 160 and 190 l/min. Six months' treatment with 2 mg/day inhaled budesonide and a long acting bronchodilator had not helped. A sweat test was normal. When he was reviewed six months after the initial presentation, examination was normal. Forced expiratory volume in one second was 65% predicted, with a flattened expiratory flow volume loop, and there was no response to bronchodilators. Chest radiography performed for the first time showed a right sided aortic arch, with tracheal compression. Bronchoscopy showed compression of the distal trachea and carina. Barium swallow highlighted two areas of extrinsic compression on the right side of the mid-oesophagus: in the lateral view there was evidence of a filling defect posteriorly in the mid-oesophagus, consistent with an aberrant left subclavian artery. A preoperative magnetic resonance image also showed a persistent left sided arch, with atretic segment. During surgery, a ligamentum arteriosum was divided. Symptoms improved after surgery, although lung function remained unchanged. Budesonide was reduced to 400 µg/day.

Case 3— An 11 year old girl, diagnosed with asthma aged 2, was referred after 18 months of increasing cough, wheeze, and chest discomfort. A chest x ray film had been reported as normal. Peak flow was virtually constant, at 150 l/min, despite the use of bronchodilators and two months' treatment with inhaled fluticasone 1 mg/day. Examination yielded a reduced volume left brachial pulse. Forced expiratory volume in one second was 75% predicted, with flattened inspiratory and expiratory flow volume loops. A repeat chest x ray film showed a right sided aortic arch, with tracheal compression (figure). Barium swallow disclosed an indentation of the oesophagus consistent with an aberrant left subclavian artery. During surgery, a ligamentum arteriosum was divided. Symptoms resolved after surgery, although flattening of the expiratory flow volume loop persisted. All treatment was discontinued.

Chest x ray film showing right sided aortic arch, with absence of left sided aortic knuckle (reproduced with parents' permission)

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Discussion

Children with asthma uncontrolled by conventional treatment need careful re-evaluation to establish the cause of symptoms. Inappropriate inhaler devices, poor adherence to treatment, or persistent provoking factors may play a part.1 Alternative diagnoses must be considered. The box lists the most common conditions that mimic or coexist with asthma.

The three children described here had symptoms of dyspnoea, chest discomfort, cough, and wheeze and a right sided aortic arch visible on a chest x ray film, associated with a vascular ring. The ring was completed by an aberrant left subclavian artery arising from the diverticulum of Kommerrel in the descending aorta and by the left sided ligamentum arteriosum, the residuum of the arterial duct. Tracheal compression resulted, causing airway obstruction and dyspnoea. Vascular rings are more commonly associated with stridor in infancy, but symptoms may develop in older children. The sensitivity and specificity for the detection of a right sided arch on chest radiography are not known but for experienced radiologists both are likely to be high. It is important to try to determine on which side the arch lies. In addition to chest radiography, simple physiological testing is useful for diagnosis. The flow volume curve shows a flattened expiratory limb, as early in expiration the large airway limits the flow. At lower lung volumes, the equal pressure point limiting the flow is in the distal bronchial generations, and the shape of the end expiratory curve is normal.2 Peak flows are consistently low, with little variability.

A right sided arch does not necessarily cause symptoms, but if the physiological abnormalities described are present, the diagnosis of vascular ring is virtually certain. Two types of right sided aortic arch can be distinguished: those with “mirror image branching,” in which a left innominate artery arises as the first branch off the aortic arch, dividing into a left common carotid and left subclavian artery, and those with an aberrant left subclavian artery, which arises as a fourth branch off the aortic arch. The first type is often associated with cyanotic heart disease, whereas the second one is usually associated with a normal heart.3 An aberrant left subclavian artery can be confirmed by barium swallow but is not of itself pathological and may be a normal variant in 1% of the population. A left sided ductus arteriosus (or ligamentum arteriosum) completes the ring, and it is this combination that can cause symptoms. In one series of 26 patients with this type of vascular ring, six had symptoms of tracheo-oesophageal compression.4 Another study reported 15 children, three of whom required division of the ring.5 If the importance of these vascular abnormalities remains unclear, a fibreoptic bronchoscopy allowing direct inspection of the airway should be performed. Surgery entails dividing the ligamentum arteriosum, thereby breaking the constricting circle. Freeing up the surrounding connective tissues from the trachea, oesophagus, and aorta further enhances this manoeuvre. After surgery, secondary tracheomalacia is almost always present after the prolonged period of airway compression. Symptoms may not resolve completely, and abnormalities of the flow volume loop may persist.

Delayed diagnosis of a vascular ring can result in unnecessary investigations and prolonged periods of ineffective treatment. Such treatment may be harmful. Inhaled corticosteroids are an effective treatment for asthma but may have adverse effects on growth, bone density, and adrenal function if used inappropriately.6 Prolonged airway compression may also be harmful. Recognition of the correct diagnosis, with consequent surgery, leads to an improvement in symptoms and withdrawal of unnecessary treatment. Consideration of alternative diagnoses, with careful inspection of the chest x ray film, is essential in the management of children with persistent respiratory symptoms.