Thoracoscopic lobectomy for an aberrant pulmonary artery of mediastinal inferior lobar branch: A case report

Introduction

We report a case of thoracoscopic surgery for a patient with an aberrant mediastinal basal pulmonary artery (A7) in the right lower lobe. The aberrant vessel flow is completely different from that of a normal pulmonary artery (PA). Thus, the surgical risk of vessel injury during right lower lobectomy is expected to increase. With extreme care, systemic inferior mediastinal nodes dissections is required.

Case report

A 69-year-old woman presented with a chief complaint of an abnormal shadow in the right lung field on chest radiography during a medical check-up, which prompted referral to our department. The patient was a non-smoker with a history of fibroid surgery. Computed tomography (CT) revealed a 14-mm solid nodule in the right lower lobe with no signs of lymph node or distant metastases. Pulmonary adenocarcinoma (cT1bN0M0) was diagnosed based on bronchoscopic biopsy. Preoperative thin-slice CT and 3D-CT showed an aberrant A7 branching from the dorsal side of the right main pulmonary artery, running from the caudal side of the middle lobe pulmonary vein to the mediastinal side of the intermediate bronchus and flowing into S7 (Figures 1 and 2(a)). The patient underwent thoracoscopic resection of the right lower lobe and lymph node dissection (ND2a-1). Interlobar dissection between the middle and lower lobes of the mediastinal side was carefully performed. The mediastinal A7 branch was confirmed between the middle lobe vein and the inferior pulmonary vein (IPV) in the anterior lung hilum (Figure 3). Prior to the transection of the lower lobe bronchus, A7 was dissected in the following order: IPV dissection, interlobar formation, dissection of the interlobar PA, and dissection of the mediastinal A7 branch. The operative time was 169 min, and the amount of blood loss was 5 mL. The histological diagnosis was solid adenocarcinoma (pT1bN0M0). The clinical course was favorable, and the patient was discharged from the hospital on the fifth day postoperatively.OPEN IN VIEWER

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Figure 2.

(a) Three-dimensional computed tomography shows the aberrant A7 (arrow) (b) Three-dimensional computed tomography of normal anatomy (c) The scheme of normal and aberrant A7.

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Figure 3.

The intraoperative findings. The aberrant A7 is located between the middle lobe and inferior pulmonary vein in the anterior lung hilum. RML, right middle lobe; RLL, right lower lobe; MV, middle lobe vein; IPV, inferior pulmonary vein; PN, phrenic nerve.

Discussion

Pulmonary artery branching varies among individuals. Subotich et al. ¹ reported that among 140 patients who underwent anatomical lung resection, variations in pulmonary blood vessels were observed in 23 patients (16.4%). The mediastinal lingular branch of the left PA is the most common anatomical variation. ¹ By contrast, a mediastinal inferior lobar branch of the right or left main PA is extremely rare,^2,3 especially on the right side. ⁴ Since 2007, for patients with thoracoscopic anatomical resections, enhanced multi-dimensional CT volume data have been used to construct pulmonary vessels from the initial two-dimensional maximum intensity projections to a three-dimensional construction in our institution. ⁵ Abnormal vessels that might be overlooked by conventional CT can be easily detected using these images which allowed us to perform a safe thoracoscopic anatomic resection.

In this study, we performed right lower lobectomy in a patient with a right aberrant mediastinal basal PA (A7). Generally, the right interlobar PA, which runs in the interlobar fissures, follows the common basal trunk and divides into two terminal branches that subsequently divide along the segmental bronchus. A6 was the first branch of the right lobar PA and A7 is the second branch in up to 70% of the cases. ⁶ Conversely, the right mediastinal inferior lobar A7, which is an anomalous branching from the right main PA, descends to the mediastinum, passes behind the middle lobe pulmonary vein, and flows into the lateral basal segment (S7). This flow is completely different from that of the normal PA. The problem with the surgical procedure was that the right interlobar PA is divided at the proximal part of the A6 branch, so the running segment of A7 was not confirmed during the right lower lobectomy. In thoracoscopic procedures, a magnified narrow view makes it difficult to grasp the wide range of anatomical structures compared to thoracotomy under direct vision. This rare abnormal branching of the PA may increase the risk of vessel injury intraoperatively. Since the proximal part of the aberrant A7 branch is located close to pericardial side of the bronchus intermedius, great care is required including during systemic inferior mediastinal nodes dissection. Preoperative evaluation of the anatomy of pulmonary vessels is important. Moreover, small A7 vessels are easily damaged by excessive tension or traction. Therefore, dissection of sufficient vessels and gentle maneuvering are required, especially when inserting an end-stapler for division.

In our surgical process, the division of the IPV first improved the deployment around the caudal side of the middle pulmonary vein where A7 is located. Following the division of the fissure between the middle and lower lobes and interlobar PA, A7 was easily divided using an end-stapler. Since injury of the branching point of the right main PA may lead to catastrophic bleeding, A7 was divided into a distal portion of this vessel near the interlobar area in this case.

Conclusion

We report a rare case of a mediastinal inferior lobar branch of the right pulmonary artery for lung cancer surgery. Our report suggests that preoperative assessment of the branching pattern of the anomalous pulmonary artery is important for a safe thoracoscopic anatomical resection.