To the best of our knowledge, this is the first study to assess the efficacy of RATS for ACT. Currently, the removal of ACT by minimally invasive procedures remains challenging for thoracic surgeons due to distinctive locations and as a consequence, thoracotomy is still the mainstream surgical approach [5, 6]. Although minimally invasive surgery significantly enhances recovery after surgery as well and is strongly encouraged currently in the thoracic field, video-assisted thoracic surgery (VATS) is less commonly used for apical chest lesions owing to its distant view and inferior exposure in ACT . RATS is an advanced modality for minimally invasive surgery that can address these associated problems. Several authors have reported their experiences using RATS for superior posterior mediastinal or paraspinal tumours [1, 3, 8–10]. However, no study has yet focussed on the efficacy of RATS on ACT. To enable radical resection and to simplify the manoeuvre, we selected well encapsulated or less invasive lesions in the apical chest, namely benign tumours according to putative diagnosis, at the start of RATS learning curve. In our small series of 15 neurogenic tumour cases, our results indicated that RATS showed promising efficacy and is an ideal alternative for ACT.
Neurogenic ACT is a subgroup pathology of superior posterior mediastinal tumours in term of its location. Previous experience in the superior posterior mediastinum can contribute to efficient removal of ACT. Massive bleeding (> 500 ml) was the most common intraoperative morbidity in superior posterior mediastinal tumours. Damage to the surrounding great vessels, such as subclavian vessels, is the most probable cause of uncontrollable haemorrhages. Also, injury to the main feeding artery of the tumour may lead to substantial bleeding, as has been reported in this case series. In cases with significant pleural adhesion, minimally invasive surgery procedures should be used with adequate assessment in ACT. Full preparation for thoracotomy must be undertaken during minimally invasive surgery . However, open surgery also possibly leads to troublesome haemorrhages, especially during the transcervical approach . In consideration of the safe and radical removal of ACT, all lesions in our case series were benign and the vast majority well encapsulated.
In addition, the prevention of nerve injury should be kept in mind during operations. Superior posterior schwannoma tumours are mostly derived from sympathetic nerves, the vagus nerve and the brachial plexus. Therefore, subcapsular enucleation or resection of the tumour may lead to nerve injury . Also, large lesions in the superior mediastinum increase the risk of surgical injury to surrounding nervous structures. Injury to sympathetic nerves results in Horner's syndrome or palmar dryness. Recurrent laryngeal nerve injury leads to hoarseness or cough. Robotic da Vinci surgical systems help surgeons to more successfully avoid unwanted damage over VATS .
Postoperative complications are less common in neurogenic lesions posterior to the mediastinum. The rate of complication varies depending on tumour aggressiveness. Nerve-related complications were most common as described above. Also, general thoracic complications such as pulmonary infection or air leakage can commonly occur. Occasionally chylous fistula and arrhythmia may also develop . Non-operative treatments are typically successful in managing these complications.
As depicted above, the prevention of intra-operative morbidity during en-bloc resection is the greatest challenge for surgeons. Robotic surgery can be successfully used in extreme thoracic locations. The stable and high-resolution three-dimensional view available to surgeons can allow accurate identification of the tumour target and adjacent structures. The working arm allows seven degrees of instrument motion and enables high dexterity in small working spaces. Tremor filtration also prevents unwanted injury to vital organs. These advantages plus better ergonomics for the surgeon and the assistant remarkedly shorten the learning curve . Bodner et al. and Podgaetz et al. believed the da Vinci robotic system could be used in broader indications in mediastinal operations compared to conventional VATS [15, 16]. Although there have been few investigations concerning the efficacy of RATS in high-seated lesions in the thoracic cavity, almost all authors show that robotic procedures are the perfect substitute for conventional thoracoscopy [1, 8, 15], closely agreeing with our results. According to our experience on mediastinal tumour resection via RATS [17, 18], we believe that RATS can be used in the treatment of superior posterior mediastinal tumours including apical chest masses.
Also, RATS can allow better exposure of the lesions in high-seated locations, especially for large tumour or adherent masses. In VATS, there are frequently extra retractions by the assistant to gain sufficient exposure to posterior mediastinal lesions . In RATS, the surgeon is normally capable of retraction with a working arm without auxiliary incision [1, 19]. Excellent operative views contribute to minimizing tissue trauma. This has been previously reported in the case by Podgaetz et al. that underwent a robotic minimally invasive surgery in the thoracic component rather than thoracotomy . In some instances, lesions extending to the neck could undergo extirpation via complete robotic procedure without accessory cervical incisions.
Since the introduction of robotic surgery into the thoracic field for superior posterior mediastinal masses, several approaches have been employed depending on the exact location of lesions. Mansour et al. used a three-arm robotic-assisted thoracoscopic technique plus an accessory port in two cases of an ectopic parathyroid gland . Xu et al  detailed a three-port technique for neurogenic ACT. In a previous case series, both approaches were used in the posterior mediastinum . Similarly, Podgaetz et al. employed a three-trocar technique for a huge thyroid goiter in the thorax . Ruurda et al. used 6 trocars to dissect a posterior mediastinal neurogenic tumour during the early initial phase of robotic use . As described in the methods section, we prefer red to utilize a 3-trocar robotic approach, normally without assistant incision. Notably, the 3-trocar technique and the 4-trocar plus one assistant port technique were also possibly used.
Satisfactory prognosis after complete resection has been previously reported in benign neurogenic tumour [1, 10]. Although we selected the most cases with clear tumour boundaries and with less possibility of infiltration, it appeared that robotic surgery can be used in more challenging indications. We treated several large lesions (> 5 cm) with significant adhesions without conversion to thoracotomy in this case series. However, we believe that a larger retrospective study is necessary to assess RATS for posterior mediastinal lesions. A prospective study, or perhaps even a randomised control trial would also be particularly informative and verify our findings.