PS is an uncommon lung tissue that lacks communication with the normal bronchial tree and receives its aberrant artery blood supply from the systemic circulation, most frequently the descending aorta . PS is classified into two main types: ILS and ELS. ILS is the most common variant, accounting for 75-93% of all PS cases [6,21,22] and 87.5% in our study. Both two types are more common in lower lobes in the literature , and all patients in our study located in lower lobes, especially in the left lower lobe. PS is a congenital and benign disease, but the potential complications are serious, which may include common pneumonia, emphysema, lung abscess, severe hemoptysis, congestive heart failure, and even malignant transformation [23-25]. Therefore, surgical resection of PS is the preferred and definitive treatment of choice after the diagnosis is made.
The conventional surgical procedure is open posterolateral thoracotomy, which is safe and feasible, however, this technique might lead to greater trauma and pain, and patients recover more slowly [3,26]. More recently many surgeons have confirmed the feasibility of VATS for PS, because of its minimally invasive, pain relief and quick recovery [10-14]. However, surgeons' pursuit of ultimate minimally invasive goals never stops. At present, UVATS has become an increasingly popular approach for surgical treatment of thoracic diseases, including PS. The potential advantages of UVATS include more intuitive vision, less postoperative pain, reduced paresthesia, and better cosmetic results compared with the conventional multiple-port VATS [27,28]. Nevertheless, UVATS remains many difficulties, as they still some controversies regarding the safety and feasibility associated with this technique, including small operating space, instruments interfering with each other and fewer entry points for introducing staplers . In addition to the PS patients, repeated infections lead to dense adhesion of the pleural cavity, and more importantly, the aberrant arteries are very concealed and difficult to handle, all of that cause great challenges for the treatment of PS by UVATS.
In our institute, we have quite a lot of UVATS experience, in addition to conventional lobectomy and segmentectomy, and many complex operations, such as bronchus sleeve lobectomy, double sleeve lobectomy, and trachea resection can be performed, which have overcome some limitations of the UVATS itself. However, to our knowledge, only several previous case reports of UVATS for PS were published [16-19]. The first challenging step is to separate the presence of extensive adhesions. The following is to make the identification and closure of the aberrant artery, which is a supply from the systemic circulation. In case of failure to safely remove aberrant arteries, it can lead to fatal catastrophic hemorrhage. In this case, it is necessary and relatively safe to follow the principle of "first abnormal blood vessels, posterior pulmonary blood vessels", priority to closure aberrant arteries.
In this study, anatomical lung resections of PS were carried out using the UAVTS approach successfully with no significant postoperative complications and no perioperative death in all 24 cases. In terms of skills and details during operation, the following conclusions are made: (i) Preoperative preparations must be sufficient, as for patients with symptoms of infection, antibiotics must be used to control the symptoms of infection, because repeated infections not only suggest that patients may have extensive pleural adhesions, but patients in the infected period are prone to postoperative sepsis, it also increases the difficulty of identifying aberrant arteries. In addition, preoperative CTA, if necessary combined with MRI or DSA, to identify the caliber and number of aberrant arteries, is essential for surgical planning. As the principle of "first abnormal blood vessels, posterior pulmonary blood vessels" is followed, it is an indispensable rule to get the basic information of the aberrant artery before surgery. (ii) The importance of a single incision is not negligible, an approximately 3 cm single incision is made in the fifth intercostal space along the anterior axillary line and slightly backward. Because the PS is basically in the lower lung, and the aberrant arteries are usually located in the inferior pulmonary ligament, and the incision is slightly backward to gain better exposure of the aberrant arteries, which can make the vision more intuitive and increase the safety of the operation. (iii) For most patients with PS, pleural adhesions are present, and 16 of our 24 patients had various kinds of adhesions. For pleural adhesions, we should carefully and alternately use electrocoagulation and ultrasonic scalpel separation, as little as possible lung injury and extensive oozing, less lung air leakage, and postoperative drainage, fully loosening adhesions, mainly increase lung freeness, easy to flip, adjust the angle, get a better surgical vision. Of course, thoracotomy or multiple-port VATS is a wise choice when the adhesions are too dense for dissection by UVATS. (iv) Before any lung resection is performed, the most important step is to find out the aberrant arteries. Combined with the preoperative images and clinical experience, the aberrant artery is mainly located in the inferior pulmonary ligament and enters the lung tissue. Note that some uncommon local sources, such as abdominal aorta and intercostal aorta, and so on, in this study, most of the aberrant arteries could be identified by preoperative CTA and other tests, without damage to aberrant arteries, the mean intraoperative blood loss was 94.17±78.90 ml (range, 10-300ml) and the most bleeding patient was 300ml, mainly due to dense adhesion of the pleural cavity. (v) Drawing on our experience, removal of the aberrant arteries should depend on their caliber and avoid blind clamping, cutting and sewing. The smaller aberrant artery was first ligated proximally using a not-resorbable suture, then proximally and distally clipped with hemo-o-Lock clips, and then finally was cut with scissors. However, the bigger aberrant artery was also first ligated proximally using a not-resorbable suture and then divided using a vascular endostapler. Due to the local infection, lacking of muscle layers and high pressure of aberrant artery, it is easy to rupture and hemorrhage, so suture ligation is very necessary to reduce the risk of bleeding. Following make sure that all aberrant arteries are processed. Sometimes more than one aberrant artery may exist, if there are any omissions, if the pulmonary veins are treated, it will cause the congestion of the lungs to occupy most of the chest, which will interfere with the surgical field and increase the risk. In addition, if the aberrant artery branch left unprocessed, it may encounter unpredictable damage that causes the aberrant arteries to retract to the mediastinum or inside the diaphragm causing uncontrollable bleeding. We strongly recommend that for a wider inferior pulmonary ligament, careful dissection must be done to ensure that the isolated aberrant arteries are not missing. Besides the number of aberrant arteries determined should be consistent with the preoperative images, and any suspect aberrant artery should be treated with caution. In our studies, one patient was found to have rapid hyperemia and swelling of the diseased lung after the inferior pulmonary vein was cutting off. Almost half of the chest cavity was occupied, and the anesthesiologist found that there was also oozing in the double-lumen endotracheal. After careful investigation, small diameter of about 8 mm was presented in the lower part of the inferior pulmonary vein originated from the descending aorta. After the dissection of this aberrant artery, hyperemia and swelling of the diseased lung and oozing in the double-lumen endotracheal were stopped. (vi) For ILS patients, although literature reported that sublobar resection was feasible, we recommend lobectomy to reduce the likelihood of recurrence. We have previously reported that the UVATS lobectomy procedure . For ELS patients; only need a mass excision, but because the anatomical location is close to the esophagus, surgery should be careful to avoid injury to the esophagus, if necessary, stomach tube can be applied to assist operation preoperative or intraoperative. (vii) Last but not least, in the surgical operation surface, especially on the stump of the aberrant arteries, the fibrin glue is covered to reduce the air leakage, exudation and drainage, so that the chest tube can be removed early and the hospital stay can be shortened.
Additionally, the potential limitations of the present study may include a small size of retrospective cases study, and a lack of statistical data analysis with other surgical approaches. In our further study, we would increase the sample size and further investigate the clinical outcomes to confirm the safety and feasibility of UVATS technique for anatomical lung resection of pulmonary sequestration.