Epidemiology
An azygos lobe is a well-known normal variant of the lung thatwas described by Wrisberg[4].The literature has pronounced its incidencefrom 0.4% on chest radiographs to 1.2% on chest CT[5–7]. It arises at any age, which varied from0.9 to 76 years(Table 1). As in our analysis, the male to femaleratio was 1.3:1 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
The superior surface of the developing lung will be sliced bythe azygos vein if the normal medial migration of the rightposterior cardinal vein over the apex of the lung fails in theembryo. The lobe medial to the azygos vein is developed as theazygos lobe. The upper lobe is separated into two parts by aslanting fissure. This abnormal fissure closely looks like a normallung fissure, ranging from the lung substance to within. It isclosed by apposition of the surfaces bounding it and is oval onsection. The addition tongue-shaped lobe isolated by the fissureand the material of it is free from macroscopic pathological changewith normal lung.
We can see the interior of the right pleural sac after removalof the right lung from picture 1(quote from Stibbe etal[8]). The upperpart of the pleural cavity is realized to be divided into twosections by a dome-like fold seen in picture 1. The fold is areduplication of the parietal pleura. Its bowed margin is attachedalong a line on the thoracic wall; the attachment that commencesposteriorly at the fifth thoracic vertebra in right thorax passesimplicitly upwards across the posterior parts of the intercostalspaces to the middle of the second rib[8]. After that it changes downwards andforwards to the first costal gristle. The azygos vein is containedbetween two layers in the fold and the pleural fold and azygos veinare related to one another[8]. The azygos vein lies behind the esophagusand on the right of the midline till it touches the level of thesixth thoracic vertebra[8]. It dips into the material of the upperlobe and pulls down with the pleural fold.
Summarizing from the literatures, the azygos lobe is dividedinto three types[8]:
Type a
More or less horizontal and cutting the outer (lateral) surfaceof the lung at some point between the apex and a point two inchesbelow the apex.
Type b
More nearly vertical and dividing the apex of the lung intolaterals halves.
Type c
Vertical and cutting off a small tongue-shaped lobe from theinner surface, the pedicle being attached to the upper margin ofthe root of the lung.
Clinical characteristics
It is very rare to find an isolated case of azygos lobe withoutany associated anomaly. From our Table, there are many primarythorax 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 radiologicalinvestigation of symptoms related to primary thorax disease. In theeight patients with lung cancer, half of them are asymptomatic,even in our case. In Delalieux et al.[9] report, however, the patient presented withhemoptysis and hoarseness. In the research of patients withspontaneous pneumothorax, most of them presented with dyspnea. 29cases diagnosed as hyperhidrosis presented with excessive sweatingtypically.
Imaging characteristics
Chest radiographs are the most generally performed imaginglearning to evaluate the mass in the thorax, but it may not bepossible to distinguish azygos lobe from others. Typical chestX-ray shows a fine, curved line suggesting the meso-azygos and asmall nodule shaped like a tear drop telling the azygosvein[9,10]. Azygos lobecan be dependably diagnosed by High-resolution chest computedtomography (HRCT). In our case, HRCT scans confirmed presence of anazygos lobe and a GGO measuring 1.2 × 1.0 cm in the anteriorsegment of the right upper lobe adjacent to the arch of the azygosvein (Figs. 2A,B).
On HDCT, the azygos vein is seen as a thicker structurefollowing the same path as the fissure. The position of the azygosarch is higher than normal one [11]. The visceral and parietal layers ofpleura forming the mesoazygos are not fused, as is shown by thecommon occurrence of pleural effusion extending into the azygosfissure [12,13]. This statefavors mobility of the azygos vein and enables it to jump from itsusual position in the fissure and migrate to the mediastinum[14]. Becausethe repositioned azygos vein is joined to a structure whoselocation is higher than the normal anatomic path of theintramediastinal azygos vein [15–18].
Treatment
In the group of patients with lung cancer, 8 cases were treatedwith surgical procedure. The first report of a right upperlobectomy by video-assisted thoracic surgery (VATS) in a patientwith an azygos lobe was published by Arai et al [10]. Some tumors may originatedirectly from the azygos lobe reported in several research[9,19,20]. In Fukuharaet al [20]research, they firstly reported the case with operativedemonstration of a primary adenocarcinoma arising from an azygoslobe, which was treated with robot-assisted azygos lobectomy. Asthe azygos lobe is a portion of the right upper lobe isolated bythe azygos vein and not a developmentally separate lobe, lobectomyin the patient with azygos lobe without concurrent resection of theright upper lobe is considered to be a limited resection[20]. However,an azygos lobectomy with mediastinal lymph node dissection may bean acceptable healing alternative for elderly individuals with poorpulmonary function and this method is considered to be a better wayfor preserving of postoperative pulmonary function and reducingmorbidity and mortality [1, 21]. Some other cardiopulmonary pathologymight be existing in patients with azygos lobe so that it isimportant to keep this in mind when examining such patients. Asshowed in our case from the Table, we approached the neoplasm withmediastinal lymph node dissection and then it was removed by VATS.The azygos lobe was visible during the operation. The upper part ofthe pleural cavity was seen to be divided into two compartments bya dome-like fold and occupied the fissure. The fold is areduplication of the parietal pleura (Fig. 3).
The presence of an azygos lobe is considered a complicatingissue, especially in cases with hyperhidrosis or spontaneouspneumothorax. An azygos lobe might have a protective effect againstthe improvement of spontaneous pneumothorax reported from somestudies [3,12,14]. Threemechanisms were offered: the reflected pleura might be limiting thesize of a potential pneumothorax; the mechanical stressestransferred to the apex of the lung will be lessening with themeso-azygos; or the changed anatomy may essentially shield againstbullae formation. As it is relatively under-inflated, there isdecreased perfusion and ventilation of the azygos lobephysiologically. The anatomical explanation for the decreasedventilation is distortion of the bronchi caused by the azygosfissure. On the other hand, the similar bronchial anatomy coulddispose the azygos lobe to air trapping and develop into emphysema,bronchiectasis, or atelectasis. VATS is used for the management ofa spontaneous pneumothorax proposing its superiority to openthoracotomy [15,17,18].
Several researches also reported the surgical difficulty inpatient with azygos lobe [22–24]. As the azygos vein is a thinwall, blood flow and very breakable structure, it has to be pushedaside or ligated with extreme carefulness[5–7, 25]. The first case was reported by Sieunarineet al [26] in1997. It was considered that difficulty would have been experiencedin achieving haemostasis in the event of injury[26]. Azygos covered thesympathetic chain between the second and fourth thoracic ganglia.The third ganglion was the most difficult one to identify duringthe surgery [22]. When there were no venous tributaries inthe curtain, it was useful to create a window to expose thesympathetic chain [22]. At the end of VATS, it is important tocheck whether the azygos lobe has gone back to its originallocation or there is a possibility of atelectasis[2–4, 22].
In patients with esophageal diseases, azygos lobe was also foundin surgery [27,28]. Two caseswere babies diagnosed as esophageal atresia. The overarching of theazygos vein in the extrapleural plane compromises the preferredextrapleural approach to the posterior mediastinum. Its apparentpassage through the upper lobe may be disconcerting, and doubtabout the anatomy depresses the surgeon from simply dividing it[27,28]. Theysuggested that once the vessel is recognized, ligation and divisionare safe and permit dissection to continue. Then Koksal et al[29] firstlyreported a child with an extralobar pulmonary sequestrations (ELPS)located in the upper posterior mediastinum associated with theazygos lobe. ELPS is a rare congenital anomaly that commonly occurson the left side [30–32]. In their case, ELPS tissue was receivingblood supply from the ascending aorta and right brachiocephalicartery, and draining to the superior vena cava by an accompanyingvein[29].