DUSTIN R. HAFERBECKER
HISTORY OF PRESENT ILLNESS
The patient was an 8-month-old girl who presented to the emergency department for the third consecutive day with parental complaints of wheezing and cough. Two days prior to admission she was examined in the emergency department, diagnosed with bronchiolitis and otitis media and discharged on amoxicillin, nebulized albuterol, and prednisolone. One day prior to admission, she was again evaluated in the emergency department for continued wheezing and cough which improved with nebulized albuterol. A chest radiograph demonstrated hyperinflation and peribronchiolar thickening. There was no cardiomegaly or pleural effusion. On the day of admission, her cough was accompanied by two episodes of perioral cyanosis. She had decreased oral intake and urine output and was febrile to 39.7°C at home.
The girl’s history was remarkable for frequent episodes of wheezing since 5 months of age. She had received nebulized albuterol intermittently, including every 4 hours for the past month, without significant improvement in her wheezing. Her cough was worse at night but did not seem to be worse with feeding or supine positioning. Her birth history was unremarkable and the prenatal ultrasound was reportedly normal.
T 38.3°C; RR 60/min; HR 110 bpm; BP 110/55 mmHg; SpO2 100% in room air
Height 25th percentile; Weight 25th percentile; Head circumference 25th percentile
Initial examination revealed a well-nourished, acyanotic infant in moderate respiratory distress. Physical examination was remarkable for purulent rhinorrhea and buccal mucosal thrush. Moderate intercostal and subcostal retractions were present. There was fair lung aeration with diffuse expiratory wheezing. No murmurs or gallops were heard on cardiac examination and femoral pulses were palpable. No hepatomegaly or splenomegaly was present.
Laboratory analysis revealed 14 600 white blood cells/mm3 with 38% segmented neutrophils, 53% lymphocytes, and no band forms. The hemoglobin was 11.0 g/dL and there were 580 000 platelets/mm3. Electrolytes, blood urea nitrogen, and creatinine were normal. Polymerase chain reaction performed on nasopharyngeal aspirate was negative for Bordetella pertussis. Antigens of adenovirus, influenza A and B viruses, parainfluenza virus types 1, 2, and 3, and respiratory syncytial virus were not detected by immunofluorescence of nasopharyngeal washings. However, respiratory syncytial virus subsequently grew in viral culture of the nasopharyngeal aspirate. Blood and urine cultures were subsequently negative.
COURSE OF ILLNESS
The patient was diagnosed with bronchiolitis, and her tachypnea and wheezing improved over time. She was treated with nebulized albuterol and oral prednisolone, with unclear benefit. She was discharged after 3 days of hospitalization, receiving albuterol every 4 hours as needed. A radionuclide milk scan was scheduled on an outpatient basis to assess the presence of gastroesophageal reflux and pulmonary aspiration.
Ten days later the patient returned to the emergency room with increased wheezing and recurrence of fever. She had poor oral intake which had not improved significantly since the last admission and was now accompanied by frequent emesis. She was admitted for treatment and further evaluation. Her radionuclide milk scan which had been performed between admissions revealed gastroesophageal reflux without pulmonary aspiration. During her current admission, careful examination of the chest radiograph suggested the diagnosis (Figures 1-1A and B). Magnetic resonance imaging (MRI) of the chest confirmed this diagnosis (Figure 1-1C).
FIGURE 1-1. A. Antero-posterior chest radiograph. B. Lateral chest radiograph. C. Chest MRI.
DISCUSSION CASE 1-1
The causes of recurrent or persistent wheezing in infant are diverse. Common causes of recurrent wheezing in infancy include bronchiolitis, reactive airways disease, and gastroesophageal reflux with microaspiration. Less commonly, recurrent wheezing is caused by congenital abnormalities of the lung or respiratory tract (congenital cystic adenomatous malformations, tracheoesophageal fistula), diaphragmatic abnormalities (paralysis of the diaphragm, congenital diaphragmatic hernia), cystic fibrosis, or immunologic defects (congenital absence of thymus, DiGeorge syndrome or other 22q11 deletion syndromes, chronic granulomatous disease, gamma globulin deficiencies). Rarely, anomalies of the major arterial branches of the aorta or pulmonary blood vessels may compress the trachea and bronchi of the infant causing acute or progressive respiratory distress. The features of this case which prompted additional evaluation included recurrent episodes of wheezing, incomplete resolution of wheezing despite prolonged beta-agonist therapy, and episodes of cyanosis.
The chest radiographs revealed a midline trachea with bilateral indentations in the anteroposterior projection (Figure 1-1A, arrows) and anterior bowing of the trachea on the lateral projection (Figure 1-1B). These findings suggested the diagnosis of double aortic arch. MRI of the chest showed the bifurcation of this double arch as the “horseshoe” structure surrounding the trachea in the center of the image (Figure 1-1C). There were no associated structural defects of the heart. The diagnosis is double aortic arch.
INCIDENCE AND ANATOMY OF VASCULAR RINGS AND SLINGS
Vascular anomalies, commonly referred to “vascular rings and slings,” can cause tracheal or esophageal compression leading to respiratory symptoms or feeding difficulty. The term vascular ring refers to any aortic arch anomaly in which the trachea and esophagus are completely surrounded by vascular structures. The vascular structures do not have to be patent. For example, a ligamentum arteriosum may complete a ring. A vascular or pulmonary sling refers to an anomaly in which vascular structures only partially surround the lower trachea but cause tracheal compression. Vascular rings are seen in less than 1% of congenital cardiac anomalies.
The most commonly occurring rings and slings are depicted in Figure 1-2.
FIGURE 1-2. Anatomy of vascular rings and slings: (A) double aortic arch; (B) right aortic arch with anomalous left subclavian artery and left ligamentum arteriosum; (C) aberrant right subclavian artery; and (D) aberrant left pulmonary artery.
Double aortic arch. This is the most common clinically recognized form of vascular ring and, as the name implies, both right and left aortic arches are present. Left and right aortic arch refer to which bronchus is crossed by the arch, not to which side of the midline the aortic root ascends. The ascending aorta divides anterior to the trachea into left and right arches, which then pass on either side of the trachea. The right arch is usually higher and larger and gives rise to the right common carotid and right subclavian arteries. The right arch travels posteriorly and indents the right side of the trachea and the right and posterior portions of the esophagus, as it passes behind the esophagus to join the left arch at the junction of the left-sided descending aorta. The left arch gives rise to the left common carotid and left subclavian arteries. The left arch is located anteriorly and indents the left side of the trachea and esophagus as it joins the descending aorta. Double aortic arch is rarely associated with congenital heart disease, but when present tetralogy of Fallot is the most common, and transposition of the great arteries is occasionally seen. Surgical division of one of the arches, usually the smaller one, is curative. Respiratory symptoms may persist for months postoperatively because of prolonged deformity of the tracheo-bronchial tree.
Aberrant right subclavian artery. This is also known as left aortic arch with retroesophageal right subclavian artery. It is the most common aortic arch malformation noted on postmortem examination. The incidence of this abnormality in the general population is approximately 0.5%. Aberrant right subclavian artery was found in 0.9% of 3427 consecutive patients undergoing cardiac catheterization at The Children’s Hospital of Philadelphia. It represented 20% of aortic arch anomalies found at catheterization. It is also seen in approximately one-third of Down syndrome patients with congenital heart disease. The left aortic arch has a normal course to the left and anterior to the trachea. However, the right subclavian artery arises as the last branch of the arch and runs posteriorly from the descending thoracic aorta to reach the right arm, passing obliquely up to and right behind the esophagus and indenting it posteriorly. Although most patients with this anomaly are asymptomatic, an older patient may complain of dysphagia. Symptomatic anterior tracheal compression results if there is a common origin of both carotid arteries in conjunction with a retroesophageal aberrant right subclavian artery. Rarely, an anomalous right subclavian artery in association with a left aortic arch, retroesophageal descending aorta, and right ligamentum arteriosum produces a symptomatic vascular ring.
Right aortic arch with anomalous left subclavian artery and left ductus arteriosus or ligamentum arteriosum. The aortic arch passes to the right of the trachea, becomes retroesophageal, and descends on left. The first branch is the left carotid artery, the second is the right carotid artery, the third the right subclavian artery, and the fourth the left subclavian artery, which arises from the descending aorta. The ductus arteriosus originates from a retroesophageal diverticulum of the descending aorta, courses to the left and connects to the pulmonary artery. Patients are usually asymptomatic. However, some patients present with wheezing or stridor because of tracheal compression and require surgical division of the ligamentum arteriosum. Older children with dysphagia may require relief of esophageal compression by actual division of the aortic arch. The retroesophageal portion is mobilized and reanastomosis of ascending and descending portions of the aorta is completed using a graft.
Aberrant left pulmonary artery (pulmonary sling). A normal pulmonary artery is absent, and the left lung is supplied by an anomalous left pulmonary artery arising from the distal right pulmonary artery. The vessel courses to the right of the trachea and then passes between the trachea and esophagus, causing compression of the right main stem bronchus, trachea, and esophagus. The resulting compression of the right main stem bronchus and trachea leads to airway obstruction, primarily affecting the right lung. Two-thirds of affected infants present in the first month of life with wheezing, stridor, or apnea. Dysphagia is rare. There may be associated collapse or hyper-inflation of the right lung. Aberrant left pulmonary artery is frequently associated with complete cartilaginous rings in the distal trachea, resulting in tracheal stenosis. It usually appears as an isolated abnormality but can be associated with other congenital cardiac defects, particularly tetralogy of Fallot. Surgical repair involves division of the left pulmonary artery from the right and reanastomosis in front of the trachea. Bronchoscopy is performed at the time of surgical repair because of the frequent association of complete cartilaginous rings causing tracheal stenosis.
CLINICAL PRESENTATION OF VASCULAR RINGS AND SLINGS
Most infants present with symptoms in early infancy. Superimposed viral infection with edema of the trachea or bronchi may account for or contribute to the respiratory symptoms. Asymptomatic infants, particularly those with aberrant right subclavian artery, are sometimes diagnosed incidentally on chest radiograph during a viral respiratory illness.
The symptoms of a vascular ring or sling are due to tracheal compression and, to a lesser degree, to esophageal compression. Symptoms of tracheal compression include wheezing, stridor, and apnea. Some infants hyperextend their necks to reduce tracheal compression. Symptoms related to esophageal compression include emesis, choking, and nonspecific feeding difficulties in infants, and dysphagia in older children. Less severe obstructions may present with recurrent respiratory infections as a result of aspiration or inadequate clearing of respiratory secretions.
Clinicians should have a high index of suspicion for a vascular anomaly in the evaluation of an infant with recurrent wheezing. Chest radiograph and barium esophagogram should be considered in the initial evaluation.
Chest radiograph. The diagnosis of a vascular ring may be suspected prior to barium esophagogram. Chest radiograph should be examined to assess laterality of the aortic arch and for evidence of tracheal or bronchial compression. The following features on chest radiograph are suggestive of a vascular anomaly and require additional evaluation: (1) A midline trachea in which there is no rotation of the patient or a sharp indentation on the right side of the trachea above the carina suggests a right aortic arch. The normal infant’s trachea is slightly displaced to the right by the normal left arch. (2) Lateral displacement of the right mediastinal pleural line indicates a right descending aorta. (3) Anterior bowing of the trachea rather than a normal posterior convexity on the lateral view indicates compression (Figure 1-1B). Generalized or focal areas of hyperinflation because of tracheal or bronchial compression can be mistakenly diagnosed as a foreign body aspiration.
Barium esophagogram. Patients with swallowing difficulties should undergo a barium swallow as part of the initial evaluation. Abnormal compression of the middle part of the esophagus posteriorly (vascular ring) or anteriorly (pulmonary sling) is typically evident.
Magnetic resonance angiography (MRA) and computed tomography angiography (CTA). Both MRA and CTA have been shown to provide excellent anatomic details and are helpful in planning reconstructive procedures.
Angiogram and transthoracic echocardiogram. In the absence of any other cardiac defect, catheter-based angiography has essentially become obsolete because of advances in three-dimensional renderings of MRA and CTA data. Transthoracic echocardiography is important to detect associated congenital cardiac defects but is less reliable at delineating vascular and tracheal anatomy.
Bronchoscopy. This enables direct visualization of compression on the trachea and is indicated when tracheal stenosis is present or suspected.
Surgical management is necessary to relieve symptomatic obstruction of trachea and esophagus. Surgery should also be considered when the infant has frequent respiratory infections or poor weight gain. The infant with severe preoperative respiratory symptoms is likely to have postoperative tracheomalacia from prolonged compression by the vascular ring. However, feeding difficulties resolve rapidly.
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