An Atypical Surgical Case of Lung Cancer With Unilateral Absence of the Pulmonary Artery, With Only the Superior Branch Remaining.

1
Introduction
UAPA is a rare congenital abnormality characterized by unilateral pulmonary artery agenesis, caused by failure of the sixth aortic arch to connect with the pulmonary trunk during embryologic development [1]. Common clinical manifestations include pulmonary hypertension (44%), recurrent pulmonary infections (37%), dyspnoea or reduced exercise tolerance (40%), and haemoptysis (20%) [2]. The presence of recurrent infections, extensive intrathoracic adhesions, and the development of collateral circulation may pose challenges during surgical procedures. We report a case of right lower lobe lung cancer with UAPA, with only the superior branch remaining, in which collateral vessels were embolized via IVR prior to surgery.

2
Case Report
Here, we describe the case of a 69‐year‐old woman who was referred to our department due to an abnormal shadow on chest radiography. She had a medical history of pneumonia and pleurisy; however, she had no episodes of haemoptysis. Contrast‐enhanced CT revealed a 19‐mm solid nodule in the right lower lobe and defects in the branches of the middle and lower lobes of the PA. No significant abnormalities of the bronchi or pulmonary veins were identified (Figure 1A,B). Ground‐glass opacities and other inflammatory changes were observed in the middle and lower lobes, suggestive of chronic airway infection (Figure 1C). Owing to the PA defect, collateral circulation developed via the right internal thoracic, bronchial, intercostal, inferior phrenic arteries and subdiaphragmatic arteries (Figure 1D,E). The solid nodule was diagnosed as an adenocarcinoma by CT‐guided biopsy. Spirometry showed a percent of predicted vital capacity (%VC) of 81.0%, and a forced expiratory volume in one second percentage (FEV1%) of 54.3%. Ventilation–perfusion scintigraphy demonstrated absent perfusion in the right middle and lower lobes, accompanied by decreased ventilation. Cardiac ultrasonography found no evidence of congenital heart defects. Surgery was planned for right lower lobe lung cancer, cT1bN0M0 cStage IA2. The day before surgery, and to mitigate the risk of bleeding during thoracotomy, we embolized the external and internal thoracic arteries along with the right fifth and sixth intercostal arteries (Figure 1F).
Intraoperative findings revealed extensive adhesions of the middle and lower lobes and numerous neovascularizations (Figure 2A). Minimal bleeding was observed during dissection as a result of preoperative embolization. Thoracotomy was performed through a 15‐cm posterior lateral incision at the fifth intercostal space. The bronchial artery was markedly enlarged (Figure 2B). Considering the potential risk of postoperative bronchial stump fistula and haemoptysis, right middle and lower lobectomies were performed with lymph node dissection (ND2a‐1). Intraoperative findings also revealed no significant abnormalities of the bronchi or pulmonary veins (Figure 2C). Subsequently, the pericardial fat pad was sutured to reinforce the bronchial stump. The pathological stage was pT2aN0M0, pStage IB. Postoperatively, the patient developed a pulmonary embolism but was discharged 10 days after surgery.

3
Discussion
UAPA is associated with recurrent respiratory infections due to bronchiectasis in the affected lung. The mechanism by which the absence of pulmonary perfusion leads to bronchial inflammation and bronchiectasis remains unclear. One hypothesis is that bronchoconstriction secondary to alveolar hypocapnia and impaired bronchial mucociliary clearance due to reduced delivery of blood‐borne inflammatory cells contribute to mucus trapping, chronic bronchitis, and subsequent bronchiectasis [3]. Furthermore, the blood supply to the affected lung is derived from systemic collateral vessels arising from the bronchial, intercostal, internal thoracic, or subdiaphragmatic arteries. Extensive intrathoracic adhesions resulting from recurrent infections and developed collateral circulation may pose challenges during surgical procedures. In this case, to reduce the risk of bleeding during thoracotomy and adhesiolysis, we performed embolization using IVR before proceeding with surgery. Owing to preoperative embolization, the operation could be completed with minimal intraoperative bleeding.
With regard to surgery, we considered the risk created by the bronchial stump fistula and therefore performed right middle and lower lobectomies. Communication between the bronchial and pulmonary arteries has been reported previously [4]. In cases where the middle lobe of the artery is absent, as in our present case, performing a lower lobectomy may potentially lead to ischemia due to the lack of blood flow from the middle lobe of the PA to the bronchial stump. Therefore, we believe that middle and lower lobectomy is appropriate in such cases, not only to prevent future haemoptysis, but also to address this risk of ischemia.
If the UAPA and lung cancer are contralateral, then the surgical strategy will differ from that applied for our present case in terms of intraoperative circulatory dynamics. Kim et al. reported that not only spirometric data but also PA pressure and right heart function should be carefully evaluated. When patients demonstrate good performance status and all test results are within normal ranges, even lobectomy may be feasible. In cases of marginal cardiopulmonary function, a preoperative pulmonary perfusion scan or a PA occlusion test may be useful for determining the extent of lung resection. One‐lung ventilation on the UAPA side for lung cancer surgery may be challenging and may require preparation for extracorporeal membrane oxygenation (ECMO) [5].

Author Contributions
Kazuhiro Okada and Shin Tanaka designed the study, prepared all the figures, and wrote the manuscript. Kazuhiro Okada, Shin Tanaka and Shinichi Toyooka performed the operation. All the authors reviewed the manuscript.

Funding
The authors have nothing to report.

Consent
The authors declare that written informed consent was obtained for the publication of this manuscript and accompanying images using the consent form provided by the Journal.

Conflicts of Interest
The authors declare no conflicts of interest.