Migratory Azygos Lobe: A Case Report

Abstract

The azygos vein sometimes merges abnormally across the right upper lobe of the lung and it hangs at the lower edge of a membranous septum, called the meso-azygos. The septum invaginates the lobe and makes a fissure. The smaller medial part of the right upper lobe is called an azygos lobe. A 16-year-old male patient was diagnosed with right-sided pneumothorax, and a closed thoracostomy was done in the emergency room. During elective wedge resection including the bulla, the meso-azygos, abnormal azygos vein, and azygos lobe were detected. We reviewed the computed tomography images and found that the azygos lobe had re-expanded laterally, not medially, to the meso-azygos after the closed thoracostomy in the emergency room. The patient had been diagnosed with left-sided pneumothorax a year ago, and no one noticed the azygos lobe at that time. We report the intraoperative findings and comparative images of a migratory azygos lobe.

Case report

A 16-year-old male patient presented to the emergency room. He complained of a sudden onset of right chest pain. A year ago, he had had a history of left-sided pneumothorax, which had been treated with a closed thoracostomy. This time, he was diagnosed with recurrent contralateral pneumothorax. A closed thoracostomy was done in the emergency room, and elective wedge resection of the right upper lobe was scheduled. During the operation, an anomalous azygos vein was found hanging along the lower edge of a membranous septum (Fig. 1A). The septum made a fissure in the right upper lobe—in other words, it partially separated the right upper lobe into 2 areas. The smaller medial area was the azygos lobe (Fig. 1B). The bulla was on the top of the larger lateral area, and wedge resection including the bulla was done. The misplaced azygos lobe was placed back in its original position at the end of the operation.

Fig. 1.

Thoracoscopic view. (A) An anomalous azygos vein (AV) is at the lower edge of the membranous septum, which is a meso-azygos (MA). The right lung is deflated. (B) The inflated azygos lobe (AL). It is in the wrong position, lateral to the membranous septum. SVC, superior vena cava.

The institutional review board waived the requirement for individual consent from the patient (IRB no., 2022-07-016; date of approval: July 19, 2022).

Discussion

The azygos vein sometimes merges abnormally across the right upper lobe of the lung. In these cases, the azygos vein hangs at the lower edge of a membranous septum, called the meso-azygos (Fig. 2) [1,2]. The septum is composed of double layers of internal parietal pleurae and external visceral pleurae [1]. The septum invaginates the right upper lobe and makes a fissure [1,3]. The smaller medial part of the lobe is called an azygos lobe.

Fig. 2.

Meso-azygos and its adjacent structures. A view of the interior of the right pleural sac after removal of the right lung and pericardium.

In 1778, the azygos lobe was first described by Heinrich Wrisberg [3] and it has been reported since then [4-7]. Its prevalence is 0.05%–0.4% on heatlh screening examinations [5]. More rarely, left azygos lobes have been reported [8]. There have been reports of bursts of bullae located in the azygos lobe [4]. However, in the present case, there was a bulla in the right upper lobe, outside of the azygos lobe.

An azygos lobe is not easy to detect, even on computed tomography, if the interpreter is not specifically interested in the possible presence of this finding. After the operation, we reviewed this patient’s computed tomography images, as well as those that had been taken a year beforehand. At that time, no one noticed the azygos lobe [2]. We did not pay particularly close attention to the right lung because we were concentrating on the left sided-pneumothorax. Interestingly, in the newer images obtained after the closed thoracostomy in the emergency room, the azygos lobe seemed to have vanished on the chest X-ray image at first glance. It was displaced laterally, not medially, to the meso-azygos [6]. Images of the migratory azygos lobe are compared in Fig. 3. We moved the azygos lobe to its original location during the operation.

Fig. 3.

Comparisons of computed tomography (CT) images of the migratory azygos lobe. The left figures were taken a year previously, and the right figures were taken at the time of the patient’s more recent presentation, between the closed thoracostomy and the operation. The azygos lobe in the right figures had re-expanded laterally to the meso-azygos after the closed thoracotomy (arrow, azygos vein; asterisk, azygos lobe). (A, B) Axial views of CT images. (C, D) Coronal views of CT images.

In general, the azygos lobe and meso-azygos themselves are not pathological anatomic variants. However, since it is not a common structure, caution is required when operating around the right lung apex with a thoracoscope [6]. In particular, when video-assisted thoracoscopic surgery is performed without 1-lung ventilation, considerable attention is required because the field of view is limited by the ventilating lung. Encountering these structures during operations for hyperhidrosis has been an unpleasant surprise for surgeons [9,10]. The meso-azygos impairs the surgical view and increases the risk of vascular injury during thoracoscopic sympathectomy [10]. Therefore, it is important to carefully check the chest X-ray image preoperatively to determine whether there is an azygos lobe or a meso-azygos [9]. Meanwhile, azygos lobes have often been discovered during treatment for pneumothorax [4-7], so the debate continues on the correlation between an azygos lobe and pneumothorax. Sadilkot et al. [7] stated that an azygos lobe is rarely associated with spontaneous pneumothorax and suggested that the presence of an azygos lobe might protect against the subsequent development of pneumothorax. However, if we happen to find an azygos lobe lateral to the meso-azygos, the previous occurrence of pneumothorax should be surmised, as in our case [1,6].

Herein, we have reported the intraoperative findings and comparative images of a migratory azygos lobe. We therefore urge readers to consider the possibility of an azygos lobe at least briefly before performing thoracic surgery around the lung apex.

Funding Statement

Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-forprofit sectors.