Case report
Herein, we report a neonate with right lung agenesis, large ventricular septal defect, partial anomalous left pulmonary artery sling, and congenital tracheal stenosis. Before birth, prenatal ultrasonography revealed right pulmonary agenesis, a ventricular septal defect, and additionally identified an abnormal vessel coursing towards the left lung in the presence of a normally formed left pulmonary artery (Supplementary Video S1). The infant was born at 38 weeks and 5 days of gestation, with a birth weight of 2,399 g (−1.56 standard deviation, 5.9th percentile). The patient developed respiratory distress at birth, which required mechanical ventilation in the neonatal ICU, followed by prolonged respiratory support with nasal continuous positive airway pressure.
Postnatal echocardiography revealed a large perimembranous ventricular septal defect with an overriding aorta, persistent left superior caval vein, patent foramen ovale, patent ductus arteriosus, partial anomalous left pulmonary artery sling, and absence of the right pulmonary artery (Figure 1(a), 1(b)). In addition to right lung agenesis and CHD, other anomalies including preaxial polydactyly of the right thumb, hypoplasia of the left second and third ribs, and hypoplasia of the third cervical vertebra were observed. Chromosomal analysis, including G-banding and microarray testing, did not reveal any abnormalities. The patent ductus arteriosus closed spontaneously on day of life 3. Oxygen saturation remained almost unchanged before and after ductal closure (approximately 97%). CT scan on day of life 5 revealed two left pulmonary arteries that encircled the bronchus (one anterior and one posterior to the left main bronchus) with no or only slight compression (Figure 2(a), 2(b), Supplementary Video S2). In addition, mild compression of the trachea by the brachiocephalic artery was observed (Figure 2(c)). Due to persistent difficulty in weaning from nasal continuous positive airway pressure, cardiac catheterisation was performed on day of life 37 to assess the indication for surgical repair of ventricular septal defect (Figure 2(d)). Results showed equal right and left ventricular pressures, a mean main pulmonary artery pressure of 25 mmHg, pulmonary vascular resistance of 2.26 Wood units·m,Reference Sun, Polin, Abman, Rowitch, Benitz and Fox2 and a pulmonary-to-systemic blood flow ratio of 1.48, as calculated using the Fick method. (Note that, since we could not advance the catheter appropriately into each left pulmonary arteries, a pressure gradient at the bifurcation could not be assessed. At least on echocardiography, no findings suggested significant stenosis, and the main pulmonary artery pressure was therefore used as a representative value for the overall pulmonary arterial pressure).
Postnatal echocardiographic findings. (a) Parasternal short-axis view showing a large perimembranous ventricular septal defect measuring 6.7 mm (indicated by the arrow). RA = right atrium; RV = right ventricle; and AO = aorta. (b) Parasternal short-axis view of the pulmonary arteries. The right pulmonary artery was absent, and two branches of the left pulmonary artery arising from the main pulmonary artery. MPA = main pulmonary artery; DA = ductus arteriosus; LPA = left pulmonary artery; and PALPA = partial anomalous left pulmonary artery.
Contrast-enhanced CT images, three-dimensional (3D) reconstruction using Viewtify (SCIEMENT, Inc., Tokyo, Japan), and angiography. (a) Left pulmonary artery (LPA) and partial anomalous left pulmonary artery (PALPA). PALPA arising from the right side and passing posterior to the left main bronchus. (b) 3D reconstruction of PALPAS. The slightly yellowish white structure represents the vascular structure, and the pink structure is the airway. AAO = ascending aorta; DAO = descending aorta; MPA = main pulmonary artery; LPA = left pulmonary artery; and PALPA = partial anomalous left pulmonary artery. A = anterior, P = posterior, R = right, L = left. (c) The brachiocephalic artery (BA) compressed the trachea. (d) Frontal view of main pulmonary artery angiography. Left pulmonary artery (LPA) arising from the left side, supplying the upper lobe. Partial anomalous left pulmonary artery (PALPA) arising from the right side, supplying the lower lobe.
The indication for surgical repair of ventricular septal defect was considered borderline based on the conventional criteria for patients with normal lungs. Thus, we hypothesised that the patient’s respiratory distress might be caused by pulmonary overcirculation to the single remaining lung. This is because all pulmonary blood flow was directed to the left lung due to right lung agenesis.Reference Akishima, Honda, Kanno, Shinoka, Hagino and Tei1 At day of life 73, the patient, who had a body weight of 4.0 kg, underwent ventricular septal defect closure via median sternotomy. Intraoperatively, bronchoscopy was performed to assess tracheal narrowing while moving the brachiocephalic artery. However, there was no significant improvement in tracheal stenosis, and no intervention was performed on the brachiocephalic artery. Postoperative echocardiography revealed a small residual shunt (approximately 1 mm) near the tricuspid valve, with a peak velocity of 4.0 m/s, indicating improvement in pulmonary hypertension. The postoperative course was uneventful. The patient was extubated on postoperative day 3 (day of life 76). Temporary nasal continuous positive airway pressure support was required, but successfully weaned by postoperative day 21 (day of life 94).
Discussion
Pulmonary agenesis is caused by failure of the lung bud to undergo the initial bifurcation into right and left branches during the early embryonic period (3–7 weeks after fertilisation).Reference Sun, Polin, Abman, Rowitch, Benitz and Fox2,Reference Plosa, Sucre, Sawyer and Gleason3 In contrast, the pulmonary arteries develop later during the embryonic period from the sixth pharyngeal arch artery.Reference van den Hoff, Wessels, Polin, Abman, Rowitch, Benitz and Fox4 In normal development, the ventral buds of the right and left sixth pharyngeal arch arteries grow towards and connect with the primitive lung vasculature arising from the primordial lung lobes, forming the right and left pulmonary arteries. The dorsal bud of the right sixth pharyngeal arch artery typically regresses. Meanwhile, the left dorsal bud persists as the ductus arteriosus. Pulmonary artery sling, which is a classic pulmonary artery anomaly, develops when the left ventral bud fails to connect with the primitive lung vasculature, resulting in the right dorsal bud forming an aberrant connection instead. Similarly, partial anomalous left pulmonary artery sling occurs when the right dorsal bud abnormally connects to a portion of the left primitive pulmonary vasculature.Reference Restrepo, Gonzalez, Baxi and Saboo5 Based on this information, the complex anatomy of the pulmonary artery in our case likely reflects the persistence of the right dorsal bud, which connected to the left lower lobe forming a partial anomalous left pulmonary artery sling, while regression of the right ventral bud resulted in the absence of the right pulmonary artery. Yen-Jun Chao et al. reported the only known case combining right pulmonary agenesis and partial anomalous left pulmonary artery sling.Reference Chao, Chen and Lin6 However, that case did not include a ventricular septal defect.
Although pulmonary hypertension can develop in cases of unilateral pulmonary agenesis even in the absence of other anomalies, its underlying mechanism remains unclear. It may present as either a primary vascular abnormality or a secondary effect of increased pulmonary blood flow directed entirely to the single remaining lung.Reference Muensterer, Abellar, Otterburn and Mathew7 Notably, the prevalence rate of pulmonary hypertension in right pulmonary agenesis is 18%. However, it increases to 88% if a left-to-right shunt is present.Reference Pool, Vogel and Blount8 These findings indicate that, even in cases similar to ours, which only involved mild elevation of the pulmonary-to-systemic blood flow ratio on cardiac catheterisation, early closure of the left-to-right shunt may help prevent pulmonary hypertension.
In addition, the improvement in respiratory status in this case may be explained by the reduction in pulmonary blood flow after shunt closure. Preoperative CT scans revealed no or only minimal signs of bronchial compression by partial anomalous left pulmonary artery sling. However, ultrasound examinations showed that the diameter of the left pulmonary artery and the partial anomalous left pulmonary artery decreased from 4.5 to 3.3 mm and from 5.0 to 3.8 mm, respectively, after surgery (Supplementary Video S3). Therefore, treating a left-to-right shunt can help relieve airway symptoms in partial anomalous left pulmonary artery sling and underscores the need for early consideration of ventricular septal defect closure.
Conclusion
We report a rare case of right pulmonary agenesis with ventricular septal defect and partial anomalous left pulmonary artery sling. Early closure of the ventricular septal defect contributed to the improvement of respiratory symptoms.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S1047951126111585.
Acknowledgements
We would like to acknowledge Dr Goro Koinuma, Dr Naoki Shimojima, Dr Yasutaka Hirata, Dr Miyuki Shibata, Dr Tetsuri Takei, Dr Yasushi Misaki, and Dr Susumu Urata for their valuable contributions to the management of this patient.
Financial support
This research received no specific grant from any funding agency, commercial, or not-for-profit sectors.
Competing interests
The author(s) declare none.
Ethical standard
Written informed consent was obtained from the parents. Ethical approval was waived according to the regulations of the ethics committee of the National Center for Child Health and Development in view of the retrospective nature of the study, and all the procedures being performed were part of the routine care.
