Mediastinal A5: a novel artery variant of the pulmonary artery system: a case report

Abstract

Background

Variations in the pulmonary artery require increased attention from thoracic surgeons prior to or during lobectomy to avoid severe intraoperative bleeding. Patients with pleural and/or hilar adhesions typically experience more intraoperative bleeding and need longer surgical time. Neglect of the variant pulmonary arteries in the context of strong adhesions may result a fatal bleeding, especially in patients with adhesions caused by pulmonary tuberculosis.

Case presentation

A 52-year-old man who presented with tuberculoma and strong hilar adhesions of the right upper lobe underwent tri-portal video-assisted thoracoscopic(VATS) lobectomy in our department. In this case, we identified a variant pulmonary artery (mediastinal A5) through three-dimensional computed tomography bronchography and angiography(3D-CTBA). It was an artery that originated from the proximal pulmonary artery trunk, and coursed between the branches of central vein and V1 + 3. The precise identification of this mediastinal A5 artery ensured a safe surgery procedure (Right upper lobectomy) without severe intraoperative bleeding. It is the first report that illustrated a variant mediastinal A5. Misdiagnosis of this variant pulmonary artery may result in severe intraoperative bleeding. 3D-CTBA which could illustrate the variant pulmonary arteries is essential in planning the surgical procedures.

Conclusion

3D-CTBA can help illustrating a variant pulmonary artery, and identification of the mediastinal A5 is essential in preforming right upper lobectomy.

Background

VATS lobectomy is an routine surgery generally for malignant pulmonary lesions, or some benign diseases. Variations in the pulmonary vasculature require increased attention from thoracic surgeons during the operation to avoid severe intraoperative bleeding.

Mediastinal lingual artery of the left upper lobe is technically challenging during the left upper lobectomy or segmentectomy. So, it is utmost to identify the variant pulmonary arteries preoperatively [1, 2]. Although it has similar origin as the mediastinal lingual artery, mediastinal A5 is located at the right side. Here, we described a variant mediastinal A5 artery of the right middle lobe in a patient with pulmonary tuberculosis. It has not been reported, and this was the first article that reported this rare variant pulmonary artery.

Case presentation

A 52-year-old male presented to our department with a pulmonary tuberculoma in the right upper lung. Chest computed tomography (CT) scans revealed a solid lesion with diameter of 2.5 cm, and tuberculosis was diagnosed by histopathology. The patient suffered from cough and had undergone HRZE therapy for half a year. However, the lung lesion still persisted, and the patient’s clinical symptoms were not relieved. No remarkable history was found in his family. Lobectomy of the right upper lung was suggested by the multidisciplinary team (MDT). A variant mediastinal A5 artery of the right middle lobe was identified on the chest CT scans. This artery, which was parallel to the right middle pulmonary artery trunk, was originated from the proximal right pulmonary trunk. Then it ran between the V1 + 3 and central vein into the right middle lobe. Three-dimensional computed tomography bronchography and angiography(3D-CTBA) clearly illustrated the routes of this variant pulmonary arteries(Fig. 1A, B and C). 3D-CTBA reconstruction was performed with the open-source 3D Slicer software (Version 4.11, United States National Institutes of Health (NIH)).

Fig. 1

3D-CTBA provides the details of the mediastinal A5. A: Mediastinal A5 located behand the SPV and V^1 + 3. B: Mediastinal A5 located between the V1 + 3 and the Central Vein. C: Mediastinal A5 originated proximal to the pulmonary artery trunk and went between the V1 + 3 and Central vein into the S5. D: Intraoperative view of the Mediastinal A5: The V^1 + 3 were divided and the stump of the V^1 + 3 were ligated to the cephalic side, the Mediastinal A5 originated proximal to the pulmonary artery trunk and located in the ventral of the Central vein. 3D-CTBA: three-dimensional computed tomography bronchography and angiography, SPV: supper pulmonary vein

This patient was placed in the left lateral decubitus position. Under general anesthesia and single-lung ventilation, the main utility incision and observation port along the anterior axillary line were made in the third and seventh intercostal spaces, respectively. One assistant incision was made in the ninth intercostal space along the posterior axillary line.

V1 and V3 were observed on the ventral surface of the right upper lung. Adequate exposure of the variant mediastinal A5 was obtained by separation of V1 and V3 with an endoscopic linear stapler. Thereafter, we observed that the central vein was located in the dorsal region of mediastinal A5 (Fig. 1). Exploration of the central vein without damaging the variant mediastinal A5 was accomplished by silk thread traction. The central vein was separated from the variant artery by dissecting the strong adhesions around them. Following dissection, A1 and A3 were separated via an endoscopic linear stapler. A2 was double ligated and separated. At last, bronchus of the right upper lobe was separated with an endoscopic linear stapler. Two catheters with a diameter of 16 mm were utilized to achieve sufficient postoperative drainage of the thoracic cavity. Owing to the identified nonmalignant diagnosis, Neither lymph node dissection nor intraoperative frozen section examination was performed. The operative time was two hours, and the intraoperative bleeding was less than 50 ml. The postoperative recovery of this patient was uneventful. So, the patient was discharged from the hospital 5 days after the surgery. Six months later, the patient got recovery from the surgery and pulmonary tuberculosis. Written informed consent was obtained from this patient. This report was approved by the ethics committee of the Public Health Clinical Center of Chengdu.

Discussion

The anatomies and variants of the pulmonary arteries have been well documented by numerous reports [3,4,5,6,7,8]. Unlike the mediastinal lingual artery which supplies the lingual segment of left upper lobe[9], mediastinal A5 has not been reported before. In this case report, the mediastinal A5 originated from the proximity of right pulmonary trunk, and posterior of superior pulmonary vein(SPV) according to the 3D-CTBA reconstruction. The mediastinal A5 which was parallel to the right middle pulmonary artery trunk, ran through the fissure of V1 + 3 and central vein into the lateral segment of the right middle lobe(S5). Similar to the mediastinal lingual artery which was originated from proximal left pulmonary artery trunk, this variant A5 artery had similar origins and courses. So, we named this novel artery as the mediastinal A⁵ artery.

The key-point of the surgery is to identify the target vessels. 3D-CTBA could identify the structure of the hilar and locations of vessels precisely compared with the standard chest CT scans. It has been reported that 3D-CTA could decrease the frequency of conversion to thoracotomy and shorten the operative time compared with traditional VATS surgeries [10]. Preoperative 3D-CTBA is an effective protocol in identifying the segmental (subsegmental) bronchi, arteries, and veins during segmentectomy [11]. In this case, relationships among the SPV, V1 + 3, central vein, mediastinal A5, A1 + 3 and right middle pulmonary artery trunk were precisely illustrated on 3D-CTBA facilitating the surgical procedures.

It is utmost important to recognize the variant artery to avoid severe intraoperative bleeding, which is the major reason to conversion to thoracotomy [12,13,14]. Previous study has reported that a variant A7 branch arising from the right main pulmonary artery proximal to the branches of the superior trunks, lying under the middle bronchus, and reaching segment S7 [4]. The anomaly in this case is also rare and easily overlooked to cause a severe vessel injury during surgical procedure. It has been reported that a variant right lower lobe segmental pulmonary artery was ligated during upper lobectomy by mistake. Failing to recognize this variant pulmonary artery can cause a serious postoperative cavitating infarction [15]. In this case, neglect of mediastinal A5 during the dissection of SPV may result in severe intraoperative bleeding. It is recommended that the mediastinal A5 was isolated long enough to decrease the tension of vessels and avoid neglect of hilar vessels during dissecting the adhesions.

Although previous study has reported a method to deal with intraoperative bleeding through uni-portal VATS approach [16], however, conversion to thoracotomy is necessary in patients with severe bleeding [17]. Upper lobectomy and history of pulmonary tuberculosis were reported to be risk factors for conversion to thoracotomy [18]. Although uni-portal VATS is routinely applied in segmentectomy and lobectomy, however, it is difficult to manage the strong hialr adhesion and complex variant pulmonary vessels through uni-portal approaches. So, in this case, we chose tri-portal VATS approach to isolate the strong adhesions around the variant pulmonary vessels and to dissect the massive lymph nodes which caused by pulmonary tuberculosis.

With the advancement of surgical instructions, Uni-portal pure robotic-assisted thoracic surgery was applied in patients with hilar and/or pleural adhesions with many advantages, such as the great comfort to the surgeon and quick and smooth recovery to the patient [19]. The robotic assisted surgery is a breakthrough for patients with variant vessels.

Conclusion

Mediastinal A5 is a rare variant pulmonary artery that needs greater attention during right upper lobectomy. 3D-CTBA is essential to identify the variant pulmonary in planning the surgical procedures.