Minimally invasive thymectomy for myasthenia gravis: the world seems to turn left

In an era of radicalism as the one we are now facing, the so-called strong thought and politically correct would like to dominate our actions. How can we translate them into Medicine? This is a goal reached over time in recent decades and we all agreed upon it for the interest of the patient and for his safety. Guidelines for diagnosis and treatment (obviously including surgery) gradually spread in our daily clinical practice. And they have gradually replaced our old habits.

The inevitable development of modern technologies has deeply influenced our approach to neoplastic and non-neoplastic thoracic diseases. Minimally invasive techniques minimize surgical trauma, shorten operative time and postoperative stay, improve outcome and cosmesis. VATS lobectomy has become the gold standard for early-stage lung cancer treatment. And even mediastinal surgery has benefitted from Minimally invasive techniques. We gradually left behind sternotomy, cervicotomy with sternal split and nowadays, VATS or robotic thymectomy have become the standard of care for non-thymomatous Myasthenia Gravis (MG) as well as for small and early-stage thymomas [1, 2].

The extent of thymus resection demonstrated to be an important prognostic factor in MG control. From the anatomic point of view, the thymus has 2 cervical poles in the neck and 2 mediastinal ones, broadly extending along the pericardium and in the anterior costophrenic recesses. Nevertheless, a variable thymic anatomy has been described and this has a profound surgical impact for the choice of the most appropriate approach. Additional ectopic thymic foci have been found in the pretracheal, subcarenal and anterior mediastinal fat, from the level of the thyroid to the diaphragm, in the aortopulmonary window, as well as from beyond each phrenic nerve, bilaterally. An extended thymectomy has been described as the en bloc surgical removal of as much thymic tissue as possible, with surrounding mediastinal fat, from the cervical region to the diaphragm, also extending laterally to both phrenic nerves, also including the aortopulmonary window [3].

In an anatomical study on human cadavers by Rückert et al. [4], the authors evaluated the possible complete mediastinal dissection in VATS, by approaching mediastinum from the left or the right side; an extended median sternotomy was thus performed for resection radicality confirmation. Results showed that thymic tissue specimen sizes and aberrant thymic tissue were not significantly different while approaching the mediastinum from the left or the right. However, the left thymic portion demonstrated to be larger and all the targeted anatomical zones were better visualized when VATS was performed from the left side. Moreover, the authors observed that incomplete tissue resection was slightly more frequent with the right approach.

In this issue of EJCTS, a retrospective multicentric International study on minimally invasive thymectomy for MG is published [5]. For the first time, the authors compare the laterality of the surgical approach with MG outcome, by adopting well-defined Myasthenia Gravis Foundation of America standards. In particular, a ‘good outcome’ was defined as postinterventional MG complete stable remission, pharmacologic remission or minimal manifestation with no MG treatment for at least 1 year. As expected from the premises of the autopsy study [4], the left-side approach demonstrated to be superior to the right one to achieve an MG ‘good outcome’, especially in case of low-class diseases. If we go through the data, the majority of interventions were robotic-assisted in about 80% of non-thymomatous patients and the rates of thymomas were quite similar between the 2 approaches. However, there is no mention about the size of thymoma nor whether its presence (and/or location) may influence the surgeon’s laterality choice. Shorter operating time and higher complete stable remission and pharmacologic remission frequency were also reported for left-side thymectomy. An overall MG ‘good outcome’ was observed in 35% of cases, significantly higher when the left approach was adopted. Furthermore, low severity Myasthenia Gravis Foundation of America class was also associated with MG ‘good outcome’.

Should we therefore adapt and convert to a left-side mediastinal approach in MG patients, translating these results into a new guideline? Quoting the ancient Romans, we can argue that Est modus in rebus.

Our belief is that the choice of the optimal surgical approach for thymectomy should consider different points: the neurological outcome (which primarily hinges on the extent of the mediastinal tissue resection), the potential morbidity of the technique and, last but not least, the patient satisfaction. The amount of tissue resected depends upon the surgeon’s commitment in pursuing the resection in terms of time and meticulous search for ectopic thymic tissue as well as the surgeon’s experience with the surgical technique adopted. On the other hand, thymectomy for MG is a potentially morbid operation that is often performed in fragile, young patients at increased risk of developing serious respiratory complications. For these reasons, the surgical approach should also minimize intraoperative and postoperative respiratory complications through a reduced operative and anaesthesia time, avoiding long periods of one-lung ventilation.

In this series, median operating time was 164 min, significantly longer for the right-side thymectomy. Minor and major postoperative complications were few and no differences between the 2 accesses were found [5]. This may suggest that when a thymectomy is performed by experienced operators, no single approach seems to be significantly superior to the others. International data on MG improvement after surgery reveal that crude remission rates (complete stable remission + pharmacologic remission) may range from 37% to 46% after trans-sternal approach [6], from 21% to 38% in the transcervical one [7] and from 14% to 40% in VATS/robotic thymectomy series [8]. The results of this series [5] are certainly in line with the data reported in the literature.

Finally, the location of thymoma may influence the laterality of minimally invasive surgical approach. The tumour, in fact, could be on the right, left or in the middle of the mediastinum and can have, even at an early stage, adhesions with adjacent anatomical structures; therefore, selecting the better way to approach thymoma is an extremely important factor. The correct oncological indications for the resection of thymoma should never be forgotten: complete surgical excision with negative margins is the paramount element in the treatment of anterior mediastinal tumours and any tumour capsule violation could radically degrade the curative intent of the thymectomy for thymoma. Given the indolent course of most thymic tumours, long-term follow-up is needed to truly validate the minimally invasive approach.

In conclusion, we believe that it is not prudent to draw any definitive conclusions on which laterality should be used in minimally invasive thymectomy: surgeons could select either approach according to their own experience and skilfulness, the predominant location of the thymus or thymoma, the presence of possible pleural adhesions as well as the need of concomitant operations, such as pulmonary resections.

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