Ann Thorac Surg 2002;73:881-886
© 2002 The Society of Thoracic Surgeons
Original article: cardiovascular
Bronchial compression by posteriorly displaced ascending aorta in patients with congenital heart disease
Yang Min Kim, MD*a,
Shi-Joon Yoo, MDd,
Woong Han Kim, MDc,
Tae Hoon Kim, MDa,
Joon Hee Joh, MDa,
Soo Jin Kim, MDb
a Department of Radiology, Sejong General Hospital & Sejong Heart Institute, Sosa-gu, Pucheon, Kyunggi-do, South Korea
b Department of Pediatrics, Sejong General Hospital & Sejong Heart Institute, Sosa-gu, Pucheon, Kyunggi-do, South Korea
c Department of Cardiac Surgery, Sejong General Hospital & Sejong Heart Institute, Sosa-gu, Pucheon, Kyunggi-do, South Korea
d Department of Diagnostic Imaging, Hospital for Sick Children, Toronto, Ontario, Canada
Accepted for publication October 16, 2001.
* Address reprint requests to Dr Yang Min Kim, Department of Radiology, Sejong General Hospital, 91-121 Sosa-dong, Sosa-gu, Pucheon, Kyunggi-do 422-711 South Korea
e-mail: ymkim11{at}be.md
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Abstract
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Background. We encountered several patients with posteriorly displaced ascending aorta and bronchial compression associated with congenital heart disease. We describe the helical computed tomography (CT) findings and explore the mechanism of airway compression.
Methods. We retrospectively reviewed the clinical data and CT findings of 8 patients with posterior displacement of the ascending aorta. The bronchial stenosis was quantified on reformatted images perpendicular to the main-stem bronchi. On an axial image at the level of main bronchi, we measured depth of retrosternal space, interaortic distance, and aorto-spinal distance. To compare with control, we measured the same variables in 10 control patients.
Results. In 7 patients, the main bronchus on the side of the aortic arch was squeezed between the ascending and descending aorta and showed slit-like stenosis. The right pulmonary artery was elongated around the ascending aorta in 5 patients and showed slit-like stenosis in 3. Patients with posterior displacement had significantly larger retrosternal space, smaller interaortic distance, and smaller aorto-spinal distance than did the control group. Aortopexy was undertaken in 3 patients. Follow-up computed tomograms of 2 patients showed improvement.
Conclusions. The posteriorly displaced ascending aorta may compress the main bronchus on the side of the aortic arch and right pulmonary artery against the descending aorta or spine. Even if the bronchial compression is mild with tolerable airway symptoms, these patients must be closely observed. When airway symptoms are severe, aortopexy should be considered.
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Introduction
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Obstruction of the major airway may complicate the natural and postoperative courses of patients with congenital heart disease. A major airway obstruction may be mistaken for a lower respiratory tract problem, as the latter is a common complication of congenital heart disease. On the other hand, early recognition of the airway obstruction is important because urgent surgical intervention is often required. When surgical treatment is contemplated, the mechanism and severity of the airway obstruction should be clearly demonstrated.
In children with congenital heart disease, major airway obstruction is most commonly associated with an aortic arch anomaly that includes double aortic arch, right aortic arch with aberrant left subclavian artery, and right aortic arch with left descending aorta [1–4]. However, major airway obstruction can also be caused by extrinsic compression by the aorta that is otherwise normally formed but is displaced or malpositioned. The latter category of major airway obstruction is seen with right lung agenesis or hypoplasia and right pneumonectomy syndrome [5–8] and is rarely seen in association with congenital heart disease [9–12]. We treated several patients with posteriorly displaced ascending aorta and compression of the main bronchus. We describe the findings of this condition on helical computed tomography (CT) and explore the mechanism responsible for the airway compression.
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Material and methods
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We retrospectively reviewed the clinical data and helical CT images of 8 children with posteriorly displaced ascending aorta associated with congenital heart disease. Patient data are summarized in Table 1.
Our study group consisted of 4 boys and 4 girls. Their ages at the time of CT scanning ranged from 4 days to 19 years (median 7 months). Their body weights ranged from 2.8 to 59 kg (median 7.3 kg). Four patients presented with airway problems, including stridor, grunting, and frequent pneumonia. One patient failed to wean from the mechanical ventilator after corrective surgery for congenital heart disease. Bronchoscopy was performed in 1 patient.
In 6 patients, helical scanning was performed under sedation with a Somatom plus 4 CT unit (Siemens, Erlangen, Germany) using 60 to 80 mg/kg of chloral hydrate. In 2 patients it was performed during breath-holding. We used a collimation width of 1 or 2 mm and a table increment of 1.6 to 3 mm. In all patients, nonionic contrast medium (Ultravist; Schering, Erlangen, Germany) was injected for vascular enhancement. Three-dimensional rendering was performed on an offline workstation (Magicview; Siemens, Germany). We evaluated the features, severity, and mechanism of airway compression. To evaluate the site and severity of the bronchial stenosis, we rendered a reformatted image perpendicular to the main bronchus showing the stenosis (Fig 1).
We also obtained reformatted images perpendicular to the contralateral bronchus and the trachea of the thoracic inlet. The severity of the bronchial stenosis was determined by comparing the area ratios between the bronchus and the trachea.
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Fig 1. Reformatted images in an oblique plane perpendicular to right and left main bronchi from 3-month-old boy. Right main bronchus (R) is flattened with decreased anteroposterior dimension and somewhat increased vertical dimension. Left main bronchus (L) is not affected.
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To explore the mechanism of airway compression by the aorta, we measured: (a) the depth of the retrosternal space, (b) the aorto-spinal distance, (c) the interaortic distance, and (d) the sterno-spinal distance (Fig 2).
For measurement, we used an axial image showing the main bronchi. We calculated the retrosternal space index (a/d), aorto-spinal distance index (b/d), and the interaortic distance index (c/d). For comparison, we derived normal control data for the above variables from 10 age-matched patients who underwent helical CT for other reasons and who showed a normal visceral arrangement, no central airway compression, and a normal position of the aortic arch. The data were analyzed using the Mann-Whitney U test. Statistical significance was considered to be present when the p value was less than 0.05.
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Fig 2. Schematic drawing of the axial CT image at the level of the main stem bronchi for measurement of control patients (left panel) and schematic drawing for comparison with patients who have posterior malpositioning of ascending aorta (right panel). (a = depth of retrosternal space [distance between posterior margin of sternum and anterior margin of ascending aorta]; b = aortospinal distance [distance between posterior margin of ascending aorta and anterior margin of spine]; c = interaortic distance [distance between posterior margin of ascending aorta and anterior margin of descending aorta]; d = sternospinal distance [distance between posterior margin of sternum and anterior margin of spine]; AA = ascending aorta; DA = descending aorta; LB = left main bronchus; RPA = right pulmonary artery; Sp = spine; St = sternum.)
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Results
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As the ascending aorta was located posteriorly in the mediastinum, the retrosternal space was widened, and the interaortic and aorto-spinal distances were decreased in all patients. Figure 3 summarizes the differences in indices between the patients and control group. Patients with posterior displacement had a significantly larger retrosternal space, a smaller interaortic distance, and a smaller aorto-spinal distance than the control group. The sizes of ascending aorta of two groups are not statistically different. The descending aorta was located in the paraspinal area in all but 1 patient, in whom it was located midline in front of the spine. Associated findings included enlargement or hypertrophy of the right ventricle in 5 patients and dilated ascending aorta in 1 patient. In the axial CT images of 6 patients, the wide retrosternal space was filled with the superiorly displaced right ventricle (Figs 4 and 5).
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Fig 3. Box plot showing differences in indices between patients and control group. (Ao = ascending aortic size divided by sternospinal distance; AS = aortospinal distance index [b/d in Fig 2]; IA = interaortic distance index [c/d in Fig 2]; RS = retrosternal space index [a/d in Fig 2]; 1 = patient group; 2 = control group.)
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Fig 4. Computed tomogram from an 8-year-old girl with ventricular septal defect. (A) Transverse CT scan shows posteriorly displaced ascending aorta (AA). Left main bronchus (arrow) is squeezed into narrow space between ascending and descending aortas (DA). A portion of right ventricle (RV) is seen in front of the ascending aorta. (B) Reformatted image along right pulmonary artery shows posteriorly displaced right pulmonary artery (R) by ascending aorta (AA). Right pulmonary artery also passes through interaortic space and is narrowed in an anteroposterior direction (arrow).
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Fig 5. Reformatted image from 15-month-old boy with patent ductus arteriosus. Curved planar reformatted image along right bronchus-carina (c)-left bronchus shows diffuse stenosis of left main bronchus (arrow). Ascending aorta (AA) is displaced posteriorly toward descending aorta (DA) and spine (sp).
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In all patients except 1 with absent right pulmonary artery, the main bronchus on the side of the aortic arch together with the right pulmonary artery pass through the space between the ascending and descending aorta (Figs 4 and 5). As the main bronchus was compressed by the posteriorly displaced ascending aorta against the descending aorta or the spine, the lumen of the involved main bronchus was flattened anteroposteriorly with an increased superoinferior dimension (Figs 1, 5, and 6).
In 6 patients with unilateral bronchial compression, the area ratio between the compressed main bronchus and the trachea ranged from 0.11 to 0.37 (mean 0.24), whereas that between the noncompressed contralateral bronchus and the trachea ranged from 0.40 to 0.59 (mean 0.48). One patient showed stenosis of both main bronchi, as airway compression occurred at the proximal bronchi near the carina. In 1 patient with an absent right pulmonary artery, the posteriorly displaced ascending aorta was not associated with airway compression. The right pulmonary artery was elongated around and compressed by the posteriorly displaced ascending aorta in 5 patients (Figs 4 and 5). It showed a decreased anteroposterior dimension and a normal craniocaudal dimension in 3 patients with left aortic arch, and diffuse hypoplasia in 2 patients with tetralogy of Fallot.
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Fig 6. Three-dimensional images from a 3-month-old boy with double-outlet right ventricle and pulmonary atresia in right aortic arch before (A) and after (B, C, and D) corrective surgery. (A) Anterior view of surface rendered image of central airway before surgery shows flattening of right main bronchus with a somewhat increased vertical dimension (arrow). (B) Anterior view of surface rendered image obtained after surgery shows severe stenosis of right main bronchus and bronchus intermedius. Bronchial lumen is completely obliterated along its medial wall due to kissing of the anterior and posterior walls of the bronchus (asterisk). (C) Maximal intensity projection image in the axial direction. Ascending aorta (AA) is posteriorly displaced, and right middle lung (RM) is herniated to left side in front of ascending aorta. Right pulmonary artery (R) and a major collateral artery (M) to the right lung pass through the space between the ascending and descending aorta (DA). (D) Curved reformatted image along the right bronchus-carina (c)-left bronchus demonstrates that part of the right bronchus (arrow) is compressed between them. Superior segment of right lower lung (RL) is collapsed.
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In 3 patients, as the airway compressions presented severe airway problems, we undertook aortopexy. This was performed after the cardiac procedure by passing two pledgeted sutures from a broad base of adventitia on both sides of the ascending aorta to the anterior wall at the edge of sternum. In 1 boy with double-outlet right ventricle and pulmonary atresia in the right aortic arch (Fig 6), the initial preoperative helical CT showed only mild flattening of the right main bronchus in an anteroposterior direction; this was ignored at the time of the study before the corrective surgery. After surgery, the patient was dependent on mechanical ventilation for more than 1 month. The follow-up CT showed emphysema of the right lung with severe stenosis of the right main bronchus between the ascending and descending aortas. The stenosis was dramatically relieved after fixation of the suspended ascending aorta to the sternum, and the patient was weaned from the mechanical ventilator. In another patient in whom a stent had been placed to relieve the stenosis of the right pulmonary artery, helical CT demonstrated severe slit-like stenosis of the left main bronchus by the displaced aorta. Bronchoscopy showed a slit-like opening of left main bronchus with pulsation. To relieve the bronchial compression and to prevent aortic rupture due to compression by the stent, we performed urgent aortopexy and surgical angioplasty of the right pulmonary artery after the removal of the stent. Two patients in whom follow-up CT was performed after the aortopexy presented improved bronchial stenosis.
Appropriate three-dimensional images for evaluation of the central airway could be reconstructed in all patients. Surface rendered images and reformatted images perpendicular to the main bronchus facilitated perception of the stenosis and accurate determination of the degree of stenosis of the obliquely oriented bronchus (Figs 1, 5, and 6). Axial maximum intensity projection images and curved reformatted images along the central airway revealed the mechanism of bronchial compression by providing the spatial relationship of the bronchus, aorta, and spine (Figs 5 and 6).
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Comment
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Although major airway obstruction due to aortic compression occurs with an aortic arch anomaly, a normally formed aorta may also cause extrinsic compression of the major airway when the aorta is dilated or displaced [9–12]. Robotin and colleagues [10] reported 2 patients with bronchial compression by the posteriorly displaced ascending aorta. The right main bronchus was reduced to a slit-like opening. They described the mechanism of airway compression as the "pincer" effect of a malposed ascending aorta and the descending aorta. These patients underwent aortopexy to relieve the airway compression.
The aorta forms an arch over the right or left main bronchus and the right pulmonary artery. Posterior displacement of the ascending aorta results in approximation of the ascending aorta to the descending aorta, thereby compromising the available space for the main bronchus on the side of the aortic arch and the right pulmonary artery. When this space is significantly compromised, the main bronchus is flattened in an anteroposterior direction between the ascending aorta and descending aorta with the spine. In the present study, we found that the retrosternal space in front of the posteriorly displaced ascending aorta was filled in part with the right ventricle, which was most often enlarged or hypertrophied. This suggests that the ascending aorta might be displaced posteriorly and probably downward because of the posterior tilting of the entire heart by the enlarged or hypertrophied right ventricle.
In contrast to evident and severe obstruction of the bronchus by the aorta in our patients, the airway symptoms or signs were not always present and were not severe. In contrast, mild bronchial compression may progress to near complete bronchial obstruction after surgery and may result in a failure to wean from the mechanical ventilation. We speculate that air trapping develops after surgery and that this triggers further bronchial compression, thus creating a vicious cycle. Therefore, when the ascending aorta is displaced posteriorly, it is important to pay attention to airway symptoms and signs for possible development of bronchial compression.
When a patient presents with significant airway symptoms caused by bronchial compression or increased right ventricular pressure resulting from compression of the right pulmonary artery due to a posteriorly displaced ascending aorta, aortopexy should be considered to relieve the compression of the main bronchus or the right pulmonary artery. In this situation, stent placement in the right pulmonary artery to relieve the stenosis is absolutely contraindicated, because stenosis of the right pulmonary artery is not due to the intrinsic narrowing but is caused by extrinsic compression of the aorta. Under these circumstances, a stent placed in the right pulmonary artery will certainly result in further compression of the adjacent main bronchus, and may lead to catastrophic rupture of the ascending aorta due to pressure erosion by the reinforced right pulmonary artery.
As bronchial compression is induced by the pulsating aorta, the bronchial stenosis associated with the posteriorly displaced ascending aorta may have a dynamic component not accurately reflected on the helical CT images. Bronchoscopy is thus required for evaluation of the dynamic component of the bronchial stenosis and in anticipation of the prognosis associated with bronchomalacia.
In conclusion, the posteriorly displaced ascending aorta in patients with congenital heart disease may compress the main bronchus on the side of the aortic arch and right pulmonary artery against the descending aorta or the spine. Even if bronchial compression is mild with and airway symptoms tolerable, such patients must be observed. When airway symptom is severe, aortopexy should be considered.
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Abstract
Introduction
