Pulmonary Arterial Anatomical Patterns: a Classification Scheme Based on Lobectomy and 3D-CTBA

Abstract

Purpose Preoperative evaluation of pulmonary vascular and tracheal routes and variations is of great importance to the surgeon. Three-dimensional computed tomography bronchography and angiography (3D-CTBA) has evolved in recent years with the optimization of 3D reconstruction techniques and artificial intelligence. We aim to apply CT angiography and Exoview 3D reconstruction technology to assess patients' pulmonary arterial tree and its anatomical variants and to try to summarize a set of anatomical typing of the pulmonary arterial tree that is relatively easy and conducive to promoting teaching based on surgical habits of lobectomy.

Methods A total of 358 patients hospitalized in the Department of Thoracic Surgery of the First Affiliated Hospital of Soochow University between July 2020 and August 2021 were included in this study. We carefully analyzed the site of emanation, alignment, and number of branches of the pulmonary artery according to a uniform classification method in conjunction with the two-dimensional CT images and transformed them into 3D reconstruction models.

Results Different types of pulmonary artery were observed in 358 cases. We evaluated the complete pulmonary artery tree and counted the number and frequency of major arteries of the pulmonary based on the surgical habits of anatomical lobectomy.

Conclusion The 3D-CTBA technique enables us to adequately assess the anatomy of the pulmonary arteries. Moreover, we provide a practical classification scheme of pulmonary arterial anatomical patterns based on lobectomy and 3D-CTBA. Our data can be used by clinicians in the teaching of pulmonary artery anatomy and the preoperative preparation for anatomical lobectomy.

Keywords

anatomy - pulmonary arteries/veins - surgery - complications - imaging (all modalities) - computed tomography

Introduction

Lobectomy is one of the common surgical procedures in thoracic surgery, which is indicated for peripheral lung cancer, irreversible lesions confined to the lobes of the lung. The procedure involves making an incision between the ribs under general anesthesia, exposing the lungs, dissecting the arteries, veins, and airways of the target lobe, and ultimately removing the lobe from the body and suturing the incision. Bleeding is one of the common perioperative complications of lobectomy. With the widespread use of thoracoscopic surgery, the operator can have a better view and be minimally invasive to some extent. However, the bronchial and vascular anatomy of the lungs is complex, with variations from time to time and significant patient individualization. Variations in pulmonary arteries often increase the risk of pulmonary artery rupture during lobectomy, which can cause massive and rapid bleeding, resulting in hemorrhagic shock, cardiac arrest, and even death. A thorough preoperative assessment of the orientation and variability of the pulmonary vasculature, including the pulmonary veins, arteries, and bronchi of each lobe, is essential to minimize the risk of hemorrhage during surgery and develop an effective preoperative surgical plan.

Several errors may be associated with the evaluation of pulmonary vasculature using conventional two-dimensional (2D) imaging analysis. In contrast, three-dimensional (3D) reconstruction of the chest refers to the process of transforming 2D imaging data, such as CT, into virtual 3D structures using 3D visualization software. Initially, it was difficult to visualize bronchial tubes and blood vessels simultaneously due to density differences, and the development of 3D computed tomography bronchography and angiography (3D-CTBA) has been limited by software and hardware as a result. In 2008, Akiba et al reported firstly that they imaged the bronchial tubes and blood vessels of a patient simultaneously and found a bronchial variant in the right upper lung at the same time, which also led to a call for the use of 3D-CTBA as a routine preoperative test for patients undergoing lung surgery.[1] 3D-CTBA has evolved in recent years with the optimization of 3D reconstruction techniques and artificial intelligence. Some studies have demonstrated the advantages of segmentectomy in the treatment of lung cancer in recent years as well,[2] [3] [4] further highlighting the importance of preoperative pulmonary vascular assessment using 3D reconstruction techniques. 3D-CTBA can help the operator to accurately identify lung segmental structures, detect anatomical variations, localize target vessels, and confirm the location of nodules, etc. In 2012, Eguchi et al[5] and Shimizu et al[6] successfully reported navigation for lung segmental resection by 3D-CTBA. However, studies on the application of 3D imaging technology to uniportal lobectomy are relatively rare. In 2008, Fukuhara et al confirmed the safety of 3D-CTBA in lobectomy.[7] In 2019, Zhang et al reported the application of this technology in uniportal single-direction right upper lobectomy, which helps to shorten the learning curve for young thoracic surgeons while ensuring that the procedure is performed safely.[8]

High-quality 3D reconstruction images of the chest can help clinicians easily recognize the anatomy, enabling accurate preoperative planning and precise intraoperative resection, thus decreasing intraoperative complications and shortening operating time. In addition, it also helps to shorten the learning curve for young thoracic surgeons. Exoview is a free and open-source 3D reconstruction software developed by our medical team and has been used in our daily clinical work with some success.[9] The purpose of this study is to apply CT angiography and Exoview 3D reconstruction technology to assess patients' pulmonary arterial tree and its anatomical variants and to try to summarize a set of anatomical typing of the pulmonary arterial tree that is relatively easy and conducive to promoting teaching based on surgical habits of lobectomy.

Patients and Methods

Patient Selection

We selected all patients (age ≥ 18 years) hospitalized in the same treatment group in the Department of Thoracic Surgery of the First Affiliated Hospital of Soochow University between July 2020 and August 2021 and collected their CT imaging data. A total of 395 patients were included in this study initially. All CT images were processed and transformed into 3D reconstruction models (including bronchial and pulmonary vessels) by Exoview software. Imaging was performed independently by two thoracic surgeons and one radiologist who carefully analyzed the site of emanation, alignment, and number of branches of the pulmonary artery according to a uniform classification method in conjunction with the 2D-CT images, and finally summarized these data. When there was disagreement among the three parties, a senior chief physician reassessed the results, and the final results were discussed and confirmed by the four parties and included in the statistics. Thirty-seven patients were excluded because of (1) patients with pulmonary isolation, (2) severe localized pulmonary vascular deformation due to a large central mass or severe bronchiectasis, (3) previous history of pulmonary surgery, and (4) inability to be imaged with poor-quality enhanced CT images. Finally, a total of 358 patients were included in this retrospective study. The study flow is shown in [Fig. 1].

Fig. 1 Study flow chart.

The study was approved by the Ethics Committee of the First Affiliated Hospital of Soochow University (Ethics Approval No. 2022043), informed consent was waived, and all data were anonymized to protect individual privacy.

Nomenclature of the Bronchi and Pulmonary Arteries

We generally followed the nomenclature of Boyden and Yamashita in describing the pulmonary arterial and bronchial structures and focused on the anatomical typing of lung segments and subsegments as described by scholars such as Nomori, Okada, and Liang Chen in their monographs. At the same time, we adjusted some of the definitions based on careful evaluation of the patient's 3D imaging and surgical practices based on anatomical lobectomy.

Nomenclature Rules for Bronchi

The corresponding bronchus is named according to the position of the lung segment and its substructures (priority is given to the superior–inferior relationship, followed by the posterior–anterior relationship, and lastly the external–internal relationship) and the first emanation of the branch. Lung segmental bronchioles were named with the letter B, specific lung segments were labeled with Arabic numerals in the upper right index position, and subsegmental bronchioles were named with lowercase English letters.

Nomenclature Rules for Pulmonary Segmental Arteries

For pulmonary segmental arteries and their branches accompanying the bronchioles of the lung segments, their nomenclature is consistent with that of the corresponding bronchioles. The pulmonary segmental arteries were named with the letter A, the specific pulmonary segmental arteries were labeled with Arabic numerals in the upper right index position, and the subsegmental arteries were named with lowercase English letters. The major branches of the right pulmonary artery are defined herein as follows: truncus superior—pulmonary artery of the first major branch to the right upper lobe; truncus intermedius—pulmonary artery between the truncus superior artery and the superior segment artery (A⁶); basal artery—A^7–10. Some of the commonly used arteries of the right upper pulmonary segment are defined as follows: recurrent artery to the posterior segment (A². rec)—a branching artery originating from the truncus anterior of the right lung, accompanying and traveling backward over the corresponding bronchiole; ascending artery to the posterior segment (A². asc)—a branching artery originating from the truncus intermedius of the right upper lung, accompanying below the corresponding bronchiole and traveling posteriorly and superiorly; ascending artery to the anterior segment (A³. asc)—a branching artery originating from the truncus intermedius of the right upper lung, accompanying the corresponding bronchiole anteriorly and inferiorly, and traveling anteriorly and superiorly.

Nomori and Okada defined the pulmonary artery between the truncus superior of the left pulmonary artery (the first major branch leading to the left upper lobe of the lung) and A⁶ as the truncus intermedius in their monograph. Based on our experience with 3D reconstruction, unlike the right pulmonary artery, in the 3D model of the left pulmonary artery, A¹⁺² and A³ tend to emanate very close to each other at the pulmonary artery (common trunk of A¹⁺² and A³ are not present in all patients), but with a different direction of travel (the former travels mainly posteriorly and superiorly and the latter anteriorly). Therefore, we suggest that the definition of the truncus intermedius of the left pulmonary artery be adjusted to the pulmonary artery between the first major branch of A¹⁺² (proximal side) and A⁶. The peripheral pulmonary artery after A⁶ branches remains defined as the interlobar artery.

Branching Patterns of Pulmonary Arteries

In our study, we mainly assessed the number of branches, common trunk and trunk length of pulmonary arteries, and classified different types of branching patterns according to them. It should be noted in particular that as shown in the [Fig. 2], a single artery originating from the main trunk is called single branch type, two arteries originating from the main trunk supplying the same area are called double branch type, and so on. In the single branch type, if branches are formed from the beginning, it is called common trunk of the artery, and the type is divided according to the number of branches further.

Fig. 2 Schematic representation of the pulmonary vessels to explain the branching patterns.

Results

We evaluated the complete pulmonary artery tree in 358 patients and counted the number and frequency of major arteries of the pulmonary based on the surgical habits of anatomical lobectomy. [Tables 1] and [2] show the branching patterns of the pulmonary arteries of the left and right lung, respectively.

Table 1 The branching patterns of the pulmonary arteries of the right lung

Branching patterns	Number of patients (%)
	(N = 358)
Truncus superior
Single branch type	322 (90.0)
Double branch type	36 (10.0)
Ascending A2	301 (84.1)
Single branch type	299 (83.5)
Double branch type	2 (0.5)
Ascending A3	136 (38.0)
Single branch type	131 (36.6)
Double branch type	5 (1.4)
Ascending A2 co-trunked with ascending A3	33 (9.2)
Middle lobe (A4 + A5)
Single branch type	129 (36.0)
from the truncus intermedius	121 (33.8)
from the basal artery	8 (2.2)
Double branch type	222 (62.0)
2 from the truncus intermedius	66 (18.4)
1 from the truncus intermedius and 1 from the basal artery	154 (43.0)
2 from the basal artery	2 (0.6)
Triple branch type	7 (2.0)
2 from the truncus intermedius and 1 from the basal artery	1 (0.3)
1 from the truncus intermedius and 2 from the basal artery	6 (1.7)
Superior segment (A6)
Single branch type	307 (85.8)
Common trunk—2 branches	50 (14.0)
Common trunk—3 branches	3 (0.8)
Common trunk—4 branches	1 (0.3)
Double branch type	50 (14.0)
Triple branch type	1 (0.3)
Basal segment
Long-trunk type	324 (90.5)
Short-trunk type	34 (9.5)

Table 2 The branching patterns of the pulmonary arteries of the left lung

Branching patterns	Number of patients (%)
	(N = 358)
Apicoposterior segment (A1+2)
Single branch type	44 (12.3)
Double branch type	166 (46.4)
Triple branch type	131 (36.6)
Quadruple branch type	17 (4.7)
Anterior segment (A3)
Single branch type	292 (81.6)
Common trunk—2 branches	41 (11.5)
Common trunk—3 branches	2 (0.6)
Double branch type	23 (6.4)
Common trunk of A1+2 and A3	221 (61.7)
Lingular segment (A4 + A5)
Mediastinal type	99 (27.7)
Single branch type	97 (27.1)
Double branch type	2 (0.6)
Interlobar type	338 (94.4)
Single branch type	237 (66.2)
Common trunk—2 branches	42 (11.7)
Common trunk—3 branches	2 (0.6)
Double branch type	99 (27.7)
Triple branch type	2 (0.6)
Superior segment (A6)
Single branch type	264 (73.7)
Common trunk—2 branches	105 (29.3)
Common trunk—3 branches	57 (15.9)
Double branch type	87 (24.3)
Triple branch type	7 (2.0)
Basal segment
Long-trunk type	190 (53.1)
Short-trunk type	168 (46.9)

Pulmonary Artery Types in the Right Upper Lung

In 90% (322/358) of the patients, a large truncus superior originated from the right pulmonary artery to supply the right upper lung ([Fig. 3A]). In 10% (36/358) of patients, the truncus superior was divided into two branches and traveled companionably over the corresponding trachea ([Fig. 3B]). In 74.6% (267/358) of the patients, the recurrent artery originated from the right truncus superior and supplied the posterior segment of the right upper lung, running above the trachea ([Fig. 3A]).

Fig. 3 The branching patterns of the pulmonary arteries of the right upper lung. (A–B) Right truncus superior. (A) Single branch type. (B) Double branch type. (C–D) Right ascending A².(C) Single branch type. (D) Double branch type. (E–G) Right ascending A³. (E) Single branch type. (F) Double branch type. (G) The common trunk of A².asc and A³.asc.

In 91.1% (326/358) of patients, the ascending artery from the truncus intermedius supplied the right upper lobe of the lung. In 84.1% (301/358) of patients, the posterior ascending artery from the truncus intermedius supplied the posterior segment of the right upper lung, traveling beneath the corresponding trachea and extending above the back. Among them, 99.3% (299/301) had a single apical artery ([Fig. 3C]), and 0.7% (2/301) had two separate arteries ([Fig. 3D]). A total of 38% (136/358) of patients had anterior ascending artery from the truncus intermedius supplying the anterior segment of the right upper lung, accompanying the corresponding trachea and traveling anteriorly and superiorly. Among them, 96.3% (131/136) had a single apical artery ([Fig. 3E]), and 3.7% (5/136) had two separate arteries ([Fig. 3F]). In addition, a total of 33 patients had ascending A² co-trunked with ascending A³ ([Fig. 3G]).

Pulmonary Artery Types in the Right Middle Lung

We categorized the right middle lobe pulmonary artery according to the number of major arteries and the originating site. A total of 36% (129/358) of the patients had a single artery, with 93.8% (121/129) originating from the truncus intermedius ([Fig. 4A]) and 6.2% (8/129) originating from the basal artery ([Fig. 4B]). A total of 62.0% (222/358) of the patients had two separate arteries. A total of 29.7% (66/222) of patients had both branches originating from the truncus intermedius ([Fig. 4C]), 69.4% (154/222) of patients had two branches originating from the truncus intermedius and the basal artery, respectively ([Fig. 4D]) and 0.9% (2/222) had both branches originating from the basal artery ([Fig. 4E]). A total of 1.9% (7/358) of the patients had three separate arteries. In one of these patients, two branches originated from the intermediate trunk and one from the basilar trunk ([Fig. 4F]); in the other six patients, two arteries originated from the basilar trunk and one from the intermediate trunk ([Fig. 4G]).

Fig. 4 The branching patterns of the pulmonary arteries of the right middle lung. (A–B) Single branch type. (A) Originating from the truncus intermedius. (B) Originating from the basal artery. (C–E) Double branch type. (C) both Originating from the truncus intermedius. (D) Originating from the truncus intermedius and the basal artery respectively. (E) Both originating from the basal artery. (F–G) Triple branch type. (F) Two arteries originated from the truncus intermedius. (G) Two arteries originated from the basal artery.

Pulmonary Artery Types in the Right Lower Lung

Based on the surgical custom of anatomical right lower lobectomy, we classified the superior segmental arteries of the right lower lung according to the number of major arteries and the presence of common trunk. The superior segment was supplied by a single branch in 85.8% (307/358) of the patients ([Fig. 5A]), two separate arteries in 14% (50/358) of the patients ([Fig. 5B]), and three separate arteries in 0.3% (1/358) of the patients ([Fig. 5C]). A total of 15.1% (54/358) of patients had a common trunk in the superior segmental arteries, of which 92.6% (50/54) had two branches ([Fig. 5D]), 5.6% (3/54) had three branches ([Fig. 5E]), and 1.9% (1/54) had four branches ([Fig. 5F]). Additionally, a total of 21 patients had a common trunk in the ascending A² and A⁶ ([Fig. 5G]). For the basal arteries, we classified them according to their trunk length. A total of 90.5% (324/358) of patients had a long common trunk ([Fig. 5G]), which we named the long-trunk type, and 9.5% (34/358) of patients had a shorter common trunk of the basal arteries (with earlier branching of the A^7–10 or the presence of a branch of the middle lobe artery emanating from the basal artery) ([Fig. 5H]), and we named this category the short-trunk type.

Fig. 5 The branching patterns of the pulmonary arteries of the right lower lung. (A–C) Right superior segmental artery. (A) Single branch type. (B) Double branch type. (C) Triple branch type. (D–F) The common trunk of the right superior segmental artery. (D) Two branches. (E) Three branches. (F) Four branches. (G–H) Right basal artery. (G) Long-trunk type. (H) Short-trunk type.

Pulmonary Artery Types in the Left Upper Lung

According to the number of major arteries of the apicoposterior segment, there were four types, including the single branch type in 12.3% (44/358) ([Fig. 6A]), double branch type in 46.4% (166/358) ([Fig. 6B]), triple branch type in 36.6% (131/358) ([Fig. 6C]), and quadruple branch type in 4.7% (17/358) ([Fig. 6D]). The phenomenon of common trunk of A¹⁺² and A³ was present in 61.7% (221/ 358) of patients. In some patients, the main trunks of the two pulmonary segmental arteries were common ([Fig. 6E]), and in others, the A³ trunk emanated tiny branching arteries that supplied the posterior apical segment together with the usual A¹⁺² ([Fig. 6F]).

Fig. 6 The branching patterns of A¹⁺² of the left upper lung. (A–D) Left apicoposterior segmental artery. (A) Single branch type. (B) Double branch type. (C) Triple branch type. (D) Quadruple branch type. (E–F) The common trunk of A¹⁺² and A³. (E) The main trunks were common. (F) A³ trunk emanated tiny branching artery.

All 358 patients had mediastinal artery of the anterior segment originating from the trunk of the left upper pulmonary artery, of which 81.6% (292/358) had a single artery ([Fig. 7A]), 6.4% (23/358) had two separate arteries ([Fig. 7B]). In some patients, the anterior segmental artery gave off branches at the beginning of its trunk. A total of 11.5% (41/358) had a double branch type ([Fig. 7C]), and 0.6% (2/358) had a triple branch type ([Fig. 7D]). In addition, tiny branch arteries originating from other sites supplying the anterior segment were present in a small percentage of patients. We found branches originating from the lingular segmental artery of the mediastinal type in 2 (0.6%) patients ([Fig. 7E]). In contrast, we found an anterior segmental artery originating from the interlobar artery, which was located distal to A¹⁺²c and proximal to A⁴, in 15 patients (4.2%) ([Fig. 7F]).

Fig. 7 The branching patterns of A³ of the left upper lung. (A–B) Left artery of the anterior segment. (A)Single branch type. (B) Double branch type. (C–D) The common trunk of A³ in the left lung. (C) Two branches. (D) Three branches. (E–F) Special branch of A³ in the left lung. (E) Originating from the mediastinal A⁴⁺⁵. (F) Originating from the interlobar artery.

The lingular segmental artery can be categorized into mediastinal type (originating from the common trunk of the left upper pulmonary artery) and interlobar type (originating from the interlobar artery) according to the location of its emanation. According to the results of our study, the mediastinal type of lingular segmental artery was present in 27.7% (99/358) of the patients and the vast majority (98%) had a single artery ([Fig. 8A]), only two patients (2%) had two separate arteries in contrast ([Fig. 8B]). The interlobar type of lingular segmental artery was present in 94.4% (338/358) of the patients, with 70.1% (237/338) having a single artery ([Fig. 8C]), 29.3% (99/338) having two separate arteries ([Fig. 8D]), and 0.6% (2/338) having three separate arteries ([Fig. 8E]). The common trunk was present in 13% (44/338) of all patients with interlobar type lingular segmental arteries, with 95.5% (42/44) in the bifurcated type ([Fig. 8F]) and 4.5% (2/44) in the trifurcated type ([Fig. 8G]).

Fig. 8 The branching patterns of the lingular segmental arteries of the left upper lung. (A–B) The lingular segmental artery of mediastinal type. (A) Single branch type. (B) Double branch type. (C–E) The lingular segmental artery of interlobar type. (C) Single branch type. (D) Double branch type. (E) Triple branch type. (F–G) The common trunk of interlobar A⁴⁺⁵ in the left lung. (F) Two branches. (G) Three branches.

Pulmonary Artery Types in the Left Lower Lung

On the same basis of the surgical habitus of anatomical left lower lobectomy, we classified the superior segmental arteries of the left lower lung according to the number of major arteries and the presence of common trunk. A total of 73.7% (264/358) of the patients had a single artery ([Fig. 9A]), 24.3% (87/358) of the patients had two separate arteries ([Fig. 9B]), and 2% (7/358) of the patients had three separate arteries ([Fig. 9C]). The common trunk of the superior segmental arteries was present in 45.3% (162/358) of the patients, with 64.8% (105/162) having a double-bifurcated type ([Fig. 9D]) and 35.2% (57/162) having a triple-bifurcated type ([Fig. 9E]). As for the interlobar arteries, we categorized them according to the length of their trunks. A total of 53.1% (190/358) of the patients had long trunks of the left lower pulmonary interlobar arteries ([Fig. 9F]), which we named the long-trunk type. A total of 46.9% (168/358) had short trunks of the interlobar arteries (with earlier branching from the main trunks by A^8–10 or due to the presence of the lingular segmental arteries of the interlobar type, the total trunk of the interlobar artery was relatively short) ([Fig. 9G]), and we named such as short-trunk type. In addition, we identified one rare case of left lower pulmonary artery of mediastinal type in our study. A⁸ originated from the common trunk of the left pulmonary artery in this patient.

Fig. 9 The branching patterns of the pulmonary arteries of the left lower lung. (A–C) Left superior segmental artery. (A) Single branch type. (B) Double branch type. (C) Triple branch type. (D–E) The common trunk of the left superior segmental artery. (D) Two branches. (E) Three branches. (F–G) Interlobar arteries of the left lower pulmonary. (F) Long-trunk type. (G) Short-trunk type.

Discussion

In 1959, Cory and Valentine evaluated local anatomical variations of the pulmonary arteries in 426 patients and performed a detailed analysis of the arterial systems of a total of 524 lungs or lobes.[10] Although they worked in great detail, the study was mainly based on the authors' intraoperative recollections and they did not specifically summarize the anatomical typing of the basal segmental arteries. In 1960, Jiayuan Jiang of Anhui Medical College used the method of injecting pigmented gelatin to plastically shape the bronchial tubes and blood vessels before stripping them off, and after an anatomical study of 85 pairs of cadaveric lungs, he published the first monograph on “Surgical Anatomy of the Broncho-Pulmonary Segments” in China, which laid the foundation of the anatomical study of lung segments. The development of medical imaging technology has pushed the research of lung bronchus and blood vessels from physical anatomy to a new stage of imaging anatomy. In 1978, Yamashita further elaborated the anatomical study of lung segments by using imaging methods in his monograph, which introduced and summarized the normal anatomy and variations of lung segments and subsegments in extreme detail. In 2008, Fukuhara confirmed the importance of 3D-CTBA in the anatomical study of lung segments and the safety of 3D-CTBA in lobectomy.[7] The results of his study showed that preoperative use of CT angiography combined with 3D reconstruction was able to accurately identify the various branches of the pulmonary artery with an accuracy of 95.2%. However, this study did not summarize the anatomical typing and variants of the pulmonary arterial tree. In 2018, Fourdrain evaluated the pulmonary arterial tree in 44 lobectomy patients using 3D reconstruction[11] and supplemented Cory and Valentine's study[10] by summarizing 11 arterial variants of the basal segment of the lungs in the typology. Japanese scholars such as Nagashima et al and Murota et al also summarized the normal anatomical typing and variants of local arteries in the lung lobes in detail based on 3D reconstruction and thin-layer CT images.[12] [13] [14]

The frequency of distribution of each branch of the pulmonary artery that we found in the present study is in general agreement with the results reported by Nomori and Okada in their monograph. However, we did not specifically summarize the subsections to which each arterial branch belonged for ease of memorization, and we have adapted and improved on some of the concepts to make them more useful for the understanding and education of anatomical lobectomy. In all patients, the truncus superior originates from the beginning of the common trunk of the right upper pulmonary artery and supplies the right upper lung, which Fourdrain called the mediastinal artery in his study.[11] However, we found that the truncus superior emanated in two branches in 10% of the patients ([Fig. 3B]). The branch vessels supplying the anterior segment in this group of patients were thicker in diameter and traveled anteriorly and superiorly over the anterior trachea from the 3D reconstruction model, whereas ascending A³ that emanate from the truncus intermedius generally appeared to have a relatively thin diameter and traveled anteriorly and superiorly over the anterior trachea from the lower part of the anterior trachea from the 3D image ([Fig. 3E–G]); therefore, we categorized and counted them separately. In contrast, these two were usually counted together in the past studies.[13] Nomori and Okada did not summarize the anatomical typology and probability of occurrence of the right middle lobe pulmonary artery in their monograph. Our findings showed that two middle lobe arteries were the most commonly present in the study cohort with a probability of 62%, which was slightly higher than those reported by Cory and Valentine[10] (57%) and Fourdrain et al[11] (54.5%). Moreover, we did not find a common trunk in the branches of the right middle lobe pulmonary artery, which may be related to the ethnicity of the study population. Based on the surgical custom of anatomical right lower lobectomy, we categorized the arteries of the superior segment of the right lower lung according to the number of major arteries and the presence of common trunk. Similar to the results reported by Nagashima et al,[14] the individual most commonly had a single artery ([Fig. 5A]) in 85.8% of cases, followed by two arteries in 14%. Nagashima et al's results were 82.6 and 17%, respectively, but the presence of a common trunk of the individual segmental arteries was not described in his study. In addition, the basal arteries were categorized according to their common trunk length into long- and short-trunk types. The common trunk of the basal artery was short in 9.5% of the patients (with early branches of A^7–10) or was relatively short due to the presence of branches of the middle lobe artery emanating from the basilar artery. Therefore, during right lower lobectomy in these patients, particular attention should be paid to the protection of the middle lobe artery, which should be carefully identified intraoperatively to avoid inadvertent injury.

Anatomical variations often occur in the left upper lung. As the most representative typology of left upper pulmonary artery variants, we found mediastinal lingual segmental arteries in 27.7% of patients, and the vast majority (98%) were unibranched ([Fig. 8A]), and Gao et al hypothesized that this type of anatomical variant might originate from the anterior segmental tracheal variant.[15] Similar to the right lower lung, the superior segmental arteries of the left lower lung were also most commonly unibranched, accounting for 73.7% of the cases, but they had significantly more common trunk than those of the right lower lung (45.3 vs. 15.1%), and the exact mechanism needs to be further investigated. Due to the presence of interlobar lingular segmental arteries, the proportion of short common trunk type of interlobar arteries in the left lower lung was significantly higher than that in the right (46.9 vs. 9.5%). In addition, mediastinal type lower pulmonary arteries are very rare, and one case of mediastinal type right lower pulmonary artery has been reported by Kawai et al[16] and Nakamura et al,[17] respectively. There was also one case of extremely rare mediastinal type left lower pulmonary artery identified in our study. Through preoperative evaluation with 3D reconstruction, we confirmed the presence of this artery by careful intraoperative dissection and successfully completed the procedure.

We also identified some uncommon drainage patterns of arteries, such as A⁴ and A⁵ both from the basal artery and mediastinal A⁸. In general, mediastinal A⁸ was not identified in previous reports. Fine anatomy of the arteries is crucial in lobectomy, and once damaged can cause disastrous consequences. These minor anatomical variations in pulmonary arteries can cause serious problems undergoing surgery. For example, we may encounter unexpected bleeding when we treat the lung fissure and the anterior mediastinal pleura if we do not have preoperative knowledge of mediastinal A⁸. Therefore, knowledge regarding minor uncommon arteries is necessary to safely perform lung resection. In this study, based on 3D-CTBA technology, combined with the surgical practice of anatomical lobectomy, we analyzed the different morphology of the pulmonary artery tree and classified the pulmonary artery tree according to the number of main arteries, the origin of the arteries, and the occurrence of common trunk phenomenon. Through the discussion of the vascular distribution of the main arteries of different pulmonary lobes, we try to provide a new perspective for the description of complex pulmonary artery morphology. For lobectomy, we found many uncommon variations through this study, and the proportion of partial variations is not low. Therefore, in the face of patients who are to undergo pulmonary resection, we should not blindly be confident to prepare according to the routine situation but should pay attention to the individualized preoperative planning for each patient. Due to the existence of these variations, we can routinely perform preoperative 3D-CTBA if conditions permit. Similarly, for young surgeons, this is a relatively simple naming and classification model. The anatomical classification of pulmonary artery tree is summarized from the perspectives of the starting position, number and whether there is a common-trunk phenomenon of pulmonary artery branches, which is helpful for beginners to understand the anatomy in an orderly sequence, also for the further learning.

There are some limitations in this study. Firstly, the inclusion of this retrospective study was for inpatients of thoracic surgery department, who themselves suffered from lung diseases and were predominantly patients with primary lung cancer, and there may have been selection bias. Secondly, one of the main purposes of this study was to facilitate young thoracic surgeons' understanding of segmental anatomy and lobectomy, so only the lung segments to which the pulmonary arteries belonged were counted, and their subsegments were not further generalized. In addition, this study did not discuss the mechanism of pulmonary artery anatomical variations, which needs to be further investigated in future studies.

Conclusion

In summary, the present study on pulmonary artery tree anatomy and variant frequencies is in general agreement with previous results in the literature. The 3D-CTBA technique provides a good perspective for recognizing pulmonary artery morphological typing and common variants. We thus provide a practical classification scheme of pulmonary arterial anatomical patterns based on lobectomy and 3D-CTBA. Our data can be used by clinicians in the teaching of pulmonary artery anatomy and the preoperative preparation for anatomical lobectomy.

Conflict of Interest

None declared.

Authors' Contribution

Data collection: Z.X., X.Z., F.L.; design of the study: X.Z., J.Z., C.L.; imaging reconstruction and data analysis: Z.X., X.Z., F.L.; drafting the manuscript: Z.X., X.Z.; critical revision of the manuscript: J.Z., C.L. Z.X., X.Z., and F.L. have contributed equally to this work.

^* These authors contributed equally to the study.

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Publication History

Received: 04 November 2023

Accepted: 26 March 2024

Article published online:
02 May 2024