Epidemiology
Azygos lobe is a rare abnormality anatomy of the lung, described by Wrisberg [4]. The literature has pronounced its incidence from 0.4% on chest radiographs to 1.2% on chest CT [5–7]. It arises at any age, which varied from 0.9 to 76 years(Table 1). As in our analysis, most of the patients are young and middle-aged male and the mean age was 36.5 years.
Table 1
Characteristics of the patients
Case | Symptoms | Localization | Accompanying disease | Treatment | Author |
1 | none | right lung | Adenocarcinoma | VATS | Samancilar.O[33] |
2 | dyspnoea | right lung | Adenocarcinoma | VATS | Shakir.H.A[19] |
3 | cough | right lung | Adenocarcinoma | RATS | Fukuhara.S[20] |
4 | none | right lung | Adenocarcinoma | VATS | Arai.H[10] |
5 | dyspnoea | right lung | Spontaneous pneumothorax | VATS | Azoury.F.M[15] |
6 | excessive sweating | right lung | Hyperhidrosis | VATS | Kauffman.P[22] |
7 | excessive sweating | right lung | Hyperhidrosis | VATS |
8 | excessive sweating | right lung | Hyperhidrosis | VATS |
9 | excessive sweating | right lung | Hyperhidrosis | VATS |
10 | excessive sweating | right lung | Hyperhidrosis | VATS |
11 | excessive sweating | right lung | Hyperhidrosis | VATS |
12 | excessive sweating | right lung | Hyperhidrosis | VATS |
13 | none | right lung | Spontaneous pneumothorax | Thoracic closed drainage | Betschart.T[16] |
14 | head injury | right lung | Spontaneous pneumothorax | Thoracic closed drainage |
15 | none | right lung | Esophageal cancer | Esophagectomy | Maldjian.P.D[27] |
16 | murmur in the mesocardiac area | right lung | Pulmonary sequestrations | Thoracotomy | Koksal.Y[29] |
17 | hemoptysis and hoarseness | right lung | Adenocarcinoma | VATS | Delalieux.S[9] |
18 | dyspnoea | right lung | Spontaneous pneumothorax | VATS | Internullo.E[17] |
19 | vomiting | right lung | Esophageal atresia | Thoracotomy | Eradi.B[28] |
20 | vomiting | right lung | Esophageal atresia | Thoracotomy |
21 | none | right lung | SCLC | VATS | Sen.S[34] |
22 | excessive sweating | right lung | Hyperhidrosis | VATS | Gill.A.J[24] |
23 | none | right lung | NSCLC | VATS | Grismer.J.T[35] |
24 | excessive sweating | right lung | Hyperhidrosis | Thoracotomy | Sieunarine.K[26] |
25 | dyspnoea | right lung | Spontaneous pneumothorax | VATS | Sadikot.R.T[18] |
26 | excessive sweating | right lung | Hyperhidrosis | VATS | Reisfeld.R[23] |
27 | excessive sweating | right lung | Hyperhidrosis | VATS |
28 | excessive sweating | right lung | Hyperhidrosis | VATS |
29 | excessive sweating | right lung | Hyperhidrosis | VATS |
30 | excessive sweating | right lung | Hyperhidrosis | VATS |
31 | excessive sweating | right lung | Hyperhidrosis | VATS |
32 | excessive sweating | right lung | Hyperhidrosis | VATS |
33 | excessive sweating | right lung | Hyperhidrosis | VATS |
34 | excessive sweating | right lung | Hyperhidrosis | VATS |
35 | excessive sweating | right lung | Hyperhidrosis | VATS |
36 | excessive sweating | right lung | Hyperhidrosis | VATS |
37 | excessive sweating | right lung | Hyperhidrosis | VATS |
38 | excessive sweating | right lung | Hyperhidrosis | VATS |
39 | excessive sweating | right lung | Hyperhidrosis | VATS |
40 | excessive sweating | right lung | Hyperhidrosis | VATS |
41 | excessive sweating | right lung | Hyperhidrosis | VATS |
42 | excessive sweating | right lung | Hyperhidrosis | VATS |
43 | excessive sweating | right lung | Hyperhidrosis | VATS |
44 | excessive sweating | right lung | Hyperhidrosis | VATS |
45 | excessive sweating | right lung | Hyperhidrosis | VATS |
46 | none | right lung | Adenocarcinoma | VATS | Our patient |
Anatomy
During the embryonic development period, if the main vein in the posterior part of the right or left thoracic cavity is displaced in the embryo at the normal medial side of the apex of the lung, the upper surface of the upper lobe in the developmental stage will be cut by the atypical vein. The lobe medial to azygos vein is developed as the azygos lobe. The upper lobe is separated into two parts by a slanting fissure. This abnormal fissure closely looks like a normal lung fissure, ranging from the lung substance to within. It is closed by apposition of the surfaces bounding it and is oval on section. The addition tongue-shaped lobe isolated by the fissure and the material of it is free from macroscopic pathological change with normal lung.
We can see the interior of the right pleural sac after removal of the right lung from picture 1(quote from Stibbe et al[8]). The azygos vein lies behind the esophagus and on the right of the midline till it touches the level of the sixth thoracic vertebra[8]. It dips into the material of the upper lobe and pulls down with the pleural fold. Summarizing from the literatures, the azygos lobe is divided into three types[8]: Type a,b and c. The difference between a and b is that the "cut line" of the upper lobe of the lung is close to horizontal or completely vertical. The c-type is the "cut line" that completely cuts the upper lobe of the lung and cuts a small tongue-shaped projection near the inner surface.
Clinical characteristics
From our Table, there are many primary thorax diseases with azygos lobe, such as lung cancer (n = 8), spontaneous pneumothorax (n = 5), esophageal cancer (n = 1), pulmonary sequestration (n = 1), esophageal atresia (n = 2), hyperhidrosis (n = 29). The azygos lobe is typically asymptomatic. It tends to be incidentally discovered during radiological investigation of symptoms related to primary thorax disease. In the eight patients with lung cancer, half of them are asymptomatic, even in our case. In Delalieux et al.[9] report, however, the patient presented with hemoptysis and hoarseness. In the research of patients with spontaneous pneumothorax, most of them presented with dyspnea. 29 cases diagnosed as hyperhidrosis presented with excessive sweating typically.
Imaging characteristics
Using the most common chest X-ray examination, we can see that the typical azygous veins appear as small nodular changes in the upper lobe of the lungs. But such changes may be overlooked by most clinicians [9, 10]. Azygos lobe can be diagnosed by High-resolution chest computed tomography (HRCT). In our case, chest The CT scan confirmed that there were azygos lobe in the right upper lobe near the tip of the lung, while a ground glass opacity (GGO) was observed on the outer side of the azygos lobe near the azygous vein whose size was 1.2 × 1.0 cm (Fig. 1A, B). On HRCT, the position of the azygos arch of the azygos lobe is relatively high compared to the normal azygos vein [11]. From an anatomical point of view, it is understood that the inner pleura is not fused with the top layer of azygos, which ultimately makes the azygos arch appear more plentiful [12, 13]. The elevation of the azygos arch will facilitate the migration of the azygous vein [14]. The azygous vein, based on the azygos arch, is more higher connected to the mediastinum than the normal anatomical path [15–18].
Treatment
In the group of patients with lung cancer, all of them were treated with surgical procedure. Arai et al reported the first case of azygos lobe in a patient with lung cancer and underwent by VATS of right upper lobectomy [10]. According to some researches, tumors may exist directly in the azygos lobe [9, 19, 20]. In Fukuhara et al [20] research, they reported that lesions present in the azygos lobe can be removed by robot-assisted minimally invasive surgery and ultimately confirmed by pathological findings as primary lung adenocarcinoma. Since the azygos lobe are not isolated, but part of the lung tissue separated from the right upper lobe, if the patient only simply removes the azygos lobe and leave the remaining part of the right upper lobe, it will be considered as a limited operation [20]. Some other cardiopulmonary pathology might be existing in patients with azygos lobe so that it is important to keep this in mind when examining such patients [1, 21]. As we showed from the table and the surgical picture, we performed a mediastinal lymph node dissection and a complete resection of the right upper lobe by VATS. During the operation, we can clearly see the azygos lobes located in the upper lobe of the right lung through the display. The area of the pleural cavity near the top of the right chest appears to be divided into two spaces. The parietal pleura and the azygous vein are connected by a dome-like fold (Fig. 2).
According to a small number of studies, in some benign lung diseases, especially in the case of hyperhidrosis or spontaneous pneumothorax, the presence of azygos lobes may be related to these diseases [3, 12, 14]. Azygos lobe has an inhibitory effect in spontaneous pneumothorax possibly. This theoretical basis is mainly derived from three possible mechanisms. Firstly, the reflexed pleura may limit the size of the potential pneumothorax; Secondly, the mechanical stress generated by the azygos lobe at the top of the lung can reduce the pleural effusion of the spontaneous pneumothorax tension in order to avoid the occurrence of pneumothorax; Thirdly, it may directly change the anatomy of the lung lobe to substantially prevent the formation of bullae. VATS is used for the management of a spontaneous pneumothorax proposing its superiority to open thoracotomy [15, 17, 18].
Several researches also reported the surgical difficulty in patient with azygos lobe [22–24]. Since the azygous vein is a thin wall, blood flow and a very fragile structure, it must be carefully pushed aside by the surgeon or ligated if necessary during surgery [5–7, 25]. Some scholars believe that it is difficult to achieve hemostasis in the case of damaged of azygous veins [26]. The Azygos vein covers the sympathetic chain between the second and fourth of thoracic ganglia. The third ganglion is the most difficult to identify ganglion in surgery and should be highly valued during surgery [22]. When venous tributaries are not seen in the surgical field, it is useful to create a operating field of exposure to the sympathetic chain for safety reasons [22]. Reminding all thoracic surgeons that at the end of the VATS, it is important to check if the azygos lobe has returned to their original position. If it does not return to its original position, there will be a problem of atelectasis. [2–4, 22].
In the group of patients with esophageal diseases, azygos lobe was also found in surgery [27, 28]. Two cases were babies diagnosed as esophageal atresia. Due to the abnormal anatomical structure of the azygous vein, the azygous lobes are produced, which makes the surgeon difficult to separate the azygous veins during the operation. In some operations, the azygous veins may not be separated successfully [27, 28]. Therefore, literature studies suggest that once the vein is found, the dissection of the azygos vein is safe. Then Koksal et al [29] firstly reported a child with an extralobar pulmonary sequestrations (ELPS). ELPS is a rare congenital lobular abnormality commonly found in the left lobes [30–32]. Under normal circumstances, ELPS receives blood supply from the ascending aorta and right brachiocephalic artery, and through the accompanying venous drainage to the superior vena cava [29].