UAPA is a rare congenital anomaly an incidence of approximately 1 in 200,000 first described by Fraentzel [6, 12]. Embryologically speaking, the proximal pulmonary artery branches develop from the proximal sixth aortic arch. UAPA occurs when the failure involution of the ipsilateral proximal sixth aortic arch with absence of the native PA and the ductus arteriosus to the hilar PA . This lesion shall be isolated or associated with other congenital heart malformations .
UAPA indicates a wide spectrum of presenting symptoms, and reports in the literature show that about 12.9–30% of patients could be asymptomatic [7, 14]. The most common clinical symptoms include recurrent respiratory infection, and exertional dyspnea, while UAPA may present hemoptysis in 18 to 20% of patients with advancing age [7, 12]. The reason of hemoptysis is generally perceived to be caused by excessive collateral circulation with age . In this study, patients were mostly diagnosed in young ages, and found with pre-cardiac murmur or respiratory distress. One patient presenting hemoptysis, who aged nearly 2 years old.
The diagnosis of UAPA may be missed in early aged patients. The chest X-ray shows the mediastinal displacement and decreased vascular markings on one side. An experienced sonographer could be able to find the diminished branch PA, calculate pulmonary artery pressure by measuring tricuspid regurgitation velocity and the abnormal lung blood supply. The images of CT could accurately show the intra-pulmonary artery distribution and the blood supply of the affected lung. The blood supply of the affected pulmonary artery includes bronchial, intercostal, subclavian, or internal thoracic arteries . Eight of 10 patients had evidence of ductal arterial supply from brachiocephalic artery to the disconnected pulmonary artery. There is a relationship between the sidedness of the aortic arch and the absent of intrapericardial PA, which supports the findings of Pfefferkorn  and Mery’s cohort . Cardio-angiography and magnetic resonance imaging also could provide hemodynamic data and accurate anatomic delineation to confirm the diagnosis and show the distal PA in the hilum .
Several literature recommended an early diagnosis and surgical intervention for UAPA. In this cohort, all the patients without TOF showed contralateral pulmonary hypertension at the time of diagnosis. Pulmonary hypertension may result from blood flow directed away from the absent pulmonary artery to the contralateral pulmonary artery. Increased blood flow leads to shear stress within the endothelium, with subsequent release of vasoconstrictive compounds. Early re-establishment of pulmonary blood flow may allow the affected lung to develop more normally and improve pulmonary hypertension . At present, there is no consensus on the optimal age for surgical correction and the surgical approach. The surgical approaches vary from connection of the affected branch PA to the main PA to temporary palliation with ductal stent or creation of an aortopulmonary shunt with definitive correction later . Murphy et al.  had performed staged surgical reconstruction of systemic shunt to the affected pulmonary artery on 7 patients at 3 months of age or younger, and concluded that early staged reconstruction could ensure subsequent growth of the pulmonary artery. Welch et al.  reported a direct anastomosis of right pulmonary artery and main pulmonary artery in a neonate and a 3-month-old infant with UAPA. By performing main pulmonary artery flap angioplasty or tube graft interposition to construct neo-PA in a series of 15 patients aged 1 day to 38 months, Kim et al.  concluded early one-stage surgical reconstruction and following transcatheter intervention on 11 patients improved pulmonary artery growth and lung perfusion. Mery et al.  published a case series with ten patients (median age: 2 years, range: 3 days to 9 years) who underwent one- and two-staged surgical repair of UAPA. Following PA centralization with interposition grafting using pericardial roll and anterior pericardial augmentation, four out of five patients required interventional procedures with balloon angioplasty and/or stent implantation during an average follow-up of 2 years. At present, there is still a controversy about the staging of surgery. The implementation of ductal stent or an aortopulmonary shunt may not only increase the preload of the left ventricular system, but also cause bilateral pulmonary hypertension. Heart failure treatment and pulmonary hypertension therapy are required .
Our series includes patients aged from 16 days to 22 months old at presentation, and these patients were in early ages when accepted the operation. We have performed single-stage collateral artery revascularized in 10 patients, who have shown accessible remnant PA at the hilum, found by CT, and the operations created superior outcomes. In this study, only one case achieved direct anastomosis, and the remaining 9 cases were indirectly matched due to the large distance and high tension. Direct anastomosis may achieve satisfactory results, and it could be done in newborns and small babies. Nevertheless, direct anastomosis cannot be applied in most cases, the duct-related tissue of the proximal end of affected branch pulmonary artery must be adequately resected to avoid stenosis or aneurysm formation. The cohort used two main surgical techniques for neo-PA reconstruction. Among them, 3 patients used Gore-Tex tube, and the remaining patients used the autologous tissue or autologous pericardium. As the child grows, the size mismatch between the graft and the native pulmonary artery shall develop, and follow-up surgery should be performed in future. More satisfactory results are received in the rest 7 patients. It is more ideal to use the autologous tissue or autologous pericardium in revascularization than any other prosthetic tubes. According to reports, the use of autologous tissue or autologous pericardium in revascularization is resistant to infection and calcification, and may have the potential for extensibility and growth . The main problem with this technique comes with the part of the tissue sutured restenosis, which is caused by shrinkage of the scar tissue. The balloon angioplasty was performed on No.4 patient during the follow-up, whose reconstruction technology of neo pulmonary artery was MPA flap angioplasty.
Meanwhile previous report recommended transection of the aorta for better visualization when creating an anastomosis between the right and the main pulmonary arteries augmented anteriorly by a pericardial patch . Moreover Moreno-Cabral et al.  reported one case that an autologous pericardial roll was placed in front of the superior vena cava and ascending aorta. With 4 years of follow-up, it was found that the anastomotic site stenosis occurred, which may be caused by compression of the ascending aorta. In our patients, the aorta and aortic arch were separated completely and retracted, a good visualization could also be obtained, and the tube was placed behind the superior vena cava and the ascending aorta to avoid the excessive tension and distortion of the neo-PA.
In the last review, there was no significant localized pulmonary artery stenosis found in these patients. All these patients showed significant growth of the affected PA. The Z value of the last ipsilateral pulmonary artery diameter significantly improved when compared to the preoperative value. In addition, no reoperation has been performed owing to the short follow-up periods.
UAPA combined with TOF is more complicated. The first successful complete repair of this defect was published by Sherrick  and the operative mortality in the past was 44 to 48% . Numerous studies have reported the repair of this defect without revascularization of the affected lung. Bockeria, L. A. et al.  concluded a result of hospital mortality of 5% in 37 patients, they suggested the NI and NI Z-score should be greater than 200 mm2/m2 and − 4 for a successful complete repair, or palliative intervention was required. Yang, T. et al.  reported a good follow-up results with no deaths in 17 patients. They also suggested using the NI and NI Z-score as a criterion to evaluate the existing pulmonary artery. Meanwhile, few studies strongly suggested simultaneous or staged revascularization of the affected lung. There were three patients with TOF underwent ipsilateral Blalock–Taussig shunt as the initial surgery followed by complete repair and one patient accepted single-stage correction in Kim’s cohort . There were 2 UAPA patients associated with TOF in this cohort. The NI and McGoon ratio meet the criterion which the previous study prescribed . The primary correction was performed with the revascularization of the affected PA. Only one patient with a lower NI and McGoon ratio occurred pulmonary hemorrhage after surgery (Patient No.4).
There are several limitations to this study. First, for it is a retrospective design of a single center, the long-term results are unclear. The anomaly is rare, so the sample size is small. It may reduce the reliability of statistical differences between certain parameters. Due to the lack of chest radiography and pulmonary vein wedge angiography data and lung perfusion scan image, the author cannot ideally distinguish the prognosis of the case. Finally, the surgery in this study was performed by three surgeons, and differences in surgical techniques may affect the results.