|Year : 2017 | Volume
| Issue : 1 | Page : 53-56
Right lung agenesis with left pulmonary artery sling: Computed tomography imaging
Sanjeev Kumar1, Munish Guleria2, Arun Sharma3
1 Department of Cardiac Radiology, C N Centre, All India Institute of Medical Sciences, New Delhi, India
2 Department of Radiology, RML-PGIMER, New Delhi, India
3 Department of Radiology, All India Institute of Medical Sciences, New Delhi, India
|Date of Web Publication||17-Jul-2017|
Department of Cardiac Radiology, Room No. 2, C N Centre, All India Institute of Medical Sciences, New Delhi
Source of Support: None, Conflict of Interest: None
We report a case of an infant with respiratory distress and difficult intubation, who on multidetector computed tomography (MDCT) imaging was found to have an extremely rare combination of left pulmonary artery (LPA) sling and right lung agenesis (RLA). The complete right-sided mediastinal shift resulted in dextroposed, coronally placed, anteriorly crossing aortic arch causing posterior displacement and significant anterior compression of the trachea. The posterior tracheal displacement and stenosis made the intubation quite difficult and challenging in this patient. Cross-sectional imaging with computed tomography angiography has an edge over echocardiography and conventional pulmonary angiography in demonstrating the anomalous posterior course of an LPA in the presence of coexisting RLA. MDCT imaging plays a pivotal role in evaluating the structural anatomy and thus provides with pertinent information regarding the cause and the level of airway obstruction.
Keywords: Difficult intubation, infant, lung/pulmonary agenesis, multidetector computed tomography imaging, pulmonary artery sling, tracheal stenosis
|How to cite this article:|
Kumar S, Guleria M, Sharma A. Right lung agenesis with left pulmonary artery sling: Computed tomography imaging. J Pract Cardiovasc Sci 2017;3:53-6
|How to cite this URL:|
Kumar S, Guleria M, Sharma A. Right lung agenesis with left pulmonary artery sling: Computed tomography imaging. J Pract Cardiovasc Sci [serial online] 2017 [cited 2023 Mar 23];3:53-6. Available from: https://www.j-pcs.org/text.asp?2017/3/1/53/210866
| Introduction|| |
The combination of right lung agenesis (RLA) and left pulmonary artery (LPA) sling is extremely rare with only few case reports in the literature. This exceptional combination along with complete tracheal rings has also been termed as pseudo-ring-sling complex. In contrast to a true ring-sling complex, the LPA in this situation has its origin directly from the main pulmonary artery (MPA) as the right pulmonary artery (RPA) is not formed.
Both these entities independently can cause obstruction of the tracheobronchial tree, thus resulting in recurrent pulmonary infections and respiratory distress to the patient. Tracheal narrowing can make the intubation difficult in these patients.,, Therefore, it is of paramount importance to correctly identify the etiology and the level of airway compromise.
We underline the vital importance of computed tomography (CT) in identifying the anatomic features and the associated anomalies of this unique combination and for localizing the level of airway stenosis along with establishing the cause of tracheobronchial narrowing in this very rare birth defect.
| Case Report|| |
A 1½-month-old male infant with unremarkable perinatal history presented in the pediatric emergency with moderate grade fever and cough for 10–12 days before admission. On examination, the infant was slightly bluish and tachypneic. There was chest wall asymmetry with the prominence of the left side. On auscultation, there was decreased air entry in the right hemithorax with crepts on the left side. The infant had hepatosplenomegaly with raised Total leucocyte count of 11,700.
Chest X-ray [Figure 1] revealed opacified right hemithorax with marked ipsilateral tracheal and mediastinal shift, raised right hemidiaphragm, and compensatory hyperinflation of the left hemithorax. Echocardiography was suggestive of dextroposed heart with normal intracardiac connections. Poor acoustic window because of extreme dextroposition limited the anatomical evaluation of heart and great vessels.
|Figure 1: Chest X-ray homogeneous opacification of right hemithorax with ipsilateral shift of whole mediastinum and trachea and hyperinflated left lung. Nasogastric tube and endotracheal tubes deviated to the right. Note is made of cervical spina bifida.|
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Multiple attempts of intubation to mitigate the respiratory distress met with failures, as the smallest size endotracheal (ET) tube was unable to even cross T1 vertebral level. Urgent thoracic multidetector CT (MDCT) angiography was done to know about the structural anatomy and to identify the cause and level of airway obstruction.
CT angiography imaging findings revealed RLA (absent right lung, bronchus, and RPA) with herniation of the left lung anteriorly. There was a complete ipsilateral mediastinal shift with dextroposed mesocardiac heart and great vessels occupying right hemithorax [Figure 2]a. Intracardiac shunts identified were a small atrial septal defect and subaortic ventricular septal defect. There was RPA agenesis with LPA originating from MPA and coursing posteriorly between the lower trachea and esophagus causing mild compression over the posterior aspect of the lower trachea at T5 vertebral level S/o LPA sling [Figure 2]b.
|Figure 2: (a and b) Axial computed tomography. Right lung agenesis (black star) with herniation of left lung (white star) anteriorly (a) right-sided mediastinal shift with dextroposed mesocardiac heart. Note is made of small atrial septal defect (b) right pulmonary artery agenesis (only right pulmonary artery stump noted) with left pulmonary artery originating from main pulmonary artery, coursing between trachea and esophagus (nasogastric tube in situ) forming a left pulmonary artery sling causing mild compression over posterior aspect of trachea.|
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Another striking imaging finding was the dextroposition of the left aortic arch due to RLA. This dextroposed aortic arch was oriented along the body's coronal plane resulting in tracheal posterior displacement with significant anterior compression of the upper trachea against T2-T3 vertebral bodies. Trachea had a further sigmoid course in the sagittal plane between the aortic arch and the anomalous LPA [Figure 3]a and [Figure 3]b.
|Figure 3: (a) Sagittal oblique reformatted. (b) Oblique axial section prependicular to trachea, (a): “S” shaped path of trachea. Initially coursing posteriorly, behind the arch and then running anterior to left pulmonary artery sling. Distal end of endotracheal tube is lying opposite C7 - T1 intervertebral level, (b): Significant indentation and compression over trachea by dextroposed coronally placed aortic arch.|
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The single left pulmonary vein had a posterior kink before it drained into LA. Right-sided pulmonary veins were absent. Right superior vena cava (SVC) had the aberrant posterior course abutting the posterior chest wall. Left SVC (LSVC) was present, draining into the right atrium through the coronary sinus.
No right bronchial bud was seen on lung window. There was evidence of a patch of consolidation/partial collapse involving an anterior segment of left upper lobe.
The note was also made of a congenital skeletal anomaly-spina bifida involving cervical vertebrae C1–C3 with a fusion of posterior elements of C2 and C3 on the right side [Figure 4].
|Figure 4: (Volume-rendering technique image): Spina bifida involving cervical vertebrae C1–C3 with fusion of posterior elements of C2 and C3 on right side. (white circle).|
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The patient was treated for pneumonitis and septicemia. Aortopexy and LPA relocation and tracheoplasty if required were planned to relieve airway obstruction.
| Discussion|| |
Pulmonary agenesis is a rare congenital anomaly characterized by complete absence of the bronchus, lung parenchyma, and pulmonary vasculature on that side. Unilateral lung agenesis has a birth prevalence of approximately 1 in 15,000. Pulmonary agenesis occurs with equal frequency in both the hemithoraces without any gender bias. RLA carries a poorer prognosis because of the larger shift of the heart and mediastinum with a consequent distortion of the great vessels, especially aortic arch resulting in extrinsic compression over the trachea anteriorly.,,,,
LPA sling is another rare congenital abnormality where the LPA originates from the RPA, hooks over the right main bronchus and courses posteriorly, taking the acute angulated retrotracheal path and thereby crossing the midline between the trachea and the esophagus to reach the left hilum. This results in a sling around lower trachea causing posterior airway compression and anterior esophageal indentation., LPA in RLA arises directly from MPA, as RPA is absent. Extrinsic tracheal compression can cause localized tracheal stenosis. More frequently, segmental tracheal narrowing is associated with both entities, often in association with complete cartilaginous rings.,
These two entities RLA and LPA sling in combination are yet more rare and present with unique complex intrathoracic anatomy, which can cause multilevel airway stenosis, delineation of which is necessary for patient management.
Embryologically, LPA sling is caused by the failure of the development or obliteration of the left 6th aortic arch when the developing left lung bud captures its vascular supply from the right 6th arch, caudal to the developing tracheobronchial tree. In RLA with LPA sling, the LPA sling starts forming in the usual manner, but the connection from the right 6th arch to the absent right postbranchial vessel does not develop. The RPA segment derived from the right 6th branchial arch persists as the vascular supply to the left lung. This description implies that in RLA, the right 6th branchial arch develops initially, despite the absence of the right lung bud, and thereafter it disappears, but only after it has made a connection to the left lung bud.,
When the mediastinum shifts into the right hemithorax, the aortic arch is tethered rightward and posteriorly by the malrotated and dextroposed heart, which then applies more tension on the trachea and left main bronchus that causes anterior compression and poor development of the tracheobronchial tree beginning in the embryonic stage. In addition, in some patients, the LPA originates from the rudimentary RPA and then curls around the carina, restricts the growth of trachea, and then constitutes a “pseudo-ring-sling” complex.
Conventional radiographic techniques for diagnosing LPA sling are chest radiography, barium esophagogram, pulmonary angiography, echocardiography, bronchoscopy, and tracheobronchography if required. Tracheobronchography and bronchoscopy can be hazardous in severe respiratory distress, rather fatal in a child with unilateral lung agenesis.
Echocardiography cannot adequately image the airways and has a relatively narrow field of view. It cannot show the complex three-dimensional (3D) relations between the lungs, heart, airways, and vascular structures as well as CT. The diagnosis of LPA sling on echocardiography in the setting of right pulmonary agenesis is made more difficult by the distortion of normal anatomy caused by cardiac malrotation and dextroposition.,
The MDCT allows high-resolution isotropic imaging and is the ideal modality for diagnosing RLA and for simultaneously identifying LPA sling and any associated tracheobronchial anomaly. MDCT can very speedily acquire volumetric data sets, allowing for 2D, multiplanar, maximum intensity projection, minimum intensity projection, and volume-rendering technique reconstructions, and has the capability to image both airway and vascular abnormalities.
The MDCT has several advantages over magnetic resonance imaging (MRI), especially for evaluating very young infants with mediastinal vascular and central airway anomalies. First, the short scanning times allow imaging of the chest in seconds, a feature that results in significantly lower sedation rates and minimizes motion artifacts. MRI has a limited role in evaluating the central airway and lung parenchyma while MDCT provides superbly detailed views of the lung parenchyma and central airways.,
Possible mechanisms of severe airway disease in RLA associated with LPA sling include:
- Extrinsic tracheal compression by the dextroposed aortic arch
- Presence of “pseudo-ring-sling complex”
- Distended pulmonary artery impinging the bronchus due to left to right shunt
- Persistent LSVC restricting the growth of trachea.
First two mechanisms mentioned above were responsible for producing symptoms of airway obstruction and pulmonary infection in our subject. The airway stenosis in our patient was largely related to an S-shaped deformation of the trachea with significant anterior compression by the aortic arch and mild posterior compression by the LPA sling. Dextroposition of the mediastinal structures may possibly have relieved the extrinsic pressure of the LPA sling avoiding the development of significant tracheal narrowing. Trachea in our subject appeared round and narrowed, raising suspicion of cartilaginous rings, though dynamic respiratory CT and bronchoscopy were not available to establish the definitive diagnosis of intrinsic tracheal stenosis. Various individual case studies in the past have corroborated these findings of airway obstruction in this subset of patients.,,,,
Intubation is really a challenging task with ET tubes remaining above the level of airway compression., Tracheal deviation, curved tracheal pathway, and tracheal narrowing due to extrinsic compression from dextroposed aortic arch were responsible for repeated intubation failures in this infant.
Other pertinent findings in our case were spina bifida with vertebral fusion anomalies and LSVC draining into the right atrium through the coronary sinus. Associated malformations of the cardiovascular, skeletal, genitourinary, and gastrointestinal systems have been described in 60% of cases of unilateral lung agenesis.
Several methods have been proposed to reduce vascular compression and intrinsic stenosis, such as mediastinal stabilization by an expansion prosthesis, aortopexy, aortic grafting, and resection, detour of the LPA, and slide tracheoplasty.
| Conclusion|| |
RLA with LPA sling is an extremely rare combination, which can result in multilevel significant airway obstruction causing respiratory distress. Intubation in these patients may at times become a challenging task. MDCT imaging not only guides us to a proper diagnosis but also can identify the etiology and level of airway narrowing, thus helping in proper patient care.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]