Robotics: Thymectomy




Introduction



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The standard treatment of isolated disorders of or related to the thymus is typically thymectomy. Indications include known or suspected thymoma, thymic carcinoid tumor, myasthenia gravis (MG) with or without concomitant thymoma, and benign thymic lesions, such as cysts or discrete hyperplasia. Regardless of the indication, complete thymectomy is the ultimate goal in order to avoid retention of ectopic thymic tissue. This is felt to be particularly important in the surgical management of MG.1 The most common surgical approach to thymectomy is the classic transsternal approach (Chapter 160), which has proved effective and safe, both in the setting of thymic neoplasms and MG.2



In the case of MG, however, many patients and neurologists are hesitant to undergo transsternal thymectomy despite evidence demonstrating clinical improvement because of concerns about perioperative morbidity, pain, and cosmesis. As a result, alternative surgical approaches were developed, including the transcervical method, the video-assisted thoracic surgery (VATS) thymectomy, and most recently robotic thymectomy. VATS thymectomy attempted to replicate complete thymectomy performed under direct, intrathoracic vision but eliminating the morbidity associated with dividing and spreading the sternum.3 Meyer et al.4 showed in a single-institution cohort study of VATS versus transsternal thymectomy for MG that there were equivalent clinical outcomes and improved perioperative results (need for postoperative ventilation and length of stay). Despite this, minimally invasive VATS thymectomy never became a widely accepted technique, and significant controversy still exists regarding the optimal surgical approach to thymectomy.



The reason for this controversy is unclear, but similar to VATS lobectomy, it is likely due to a combination of factors, including the technical limitations of an unstable two-dimensional camera platform and limited maneuverability of instrumentation. These issues are especially enhanced in the limited confines of the anterior mediastinum. It was precisely for this application that the master–slave robotic surgical system was developed (da Vinci Surgical System; Intuitive Surgical, Sunnyvale, CA). The three-dimensional (3D) visual system and wristed instrumentation was specifically designed for closed chest cardiothoracic surgery in the anterior and middle mediastinum. However, while this original indication has never been widely realized, other indications evolved, including thymectomy. The earliest case reports consist of only patients with nonthymomatous MG,5,6 but subsequent series have included those with encapsulated thymic lesions as well.710



This chapter reviews the general principles and clinical aspects of robotic thymectomy with an emphasis on patient selection, preoperative preparation, technical aspects, and perioperative outcomes.




General Principles



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The guiding principle that must be remembered when one is considering utilizing robotic surgical systems for thymectomy is that the ultimate goal is to perform complete resection without violating the capsule of the thymus or any associated lesion. It is up to the surgeon to decide whether this can be safely and appropriately achieved though a minimally invasive robotic approach. The incision strategy, conduct of the procedure, and postoperative management between VATS and robotic thymectomy are similar. Ruckert et al.11 were among the first to standardize the steps of minimally invasive thymectomy into a 10-step procedure. In their single-institution retrospective study, they compared outcomes of using this standard approach by VATS or robotics in a cohort of matched patients with MG and showed that while immediate perioperative outcomes were indistinguishable, on the basis of long-term follow-up (42 months) those treated by robotics had a higher cumulative complete remission rate (39.25% vs. 20.3%, p = 0.01).



In the case of thymic neoplasms, the size, location (right- or left-side predominant) and extent of lesion, influence the choice of operative approach, yet these are not the most compelling factors in deciding whether robotic assistance is feasible. Rather, how these factors determine the likelihood of achieving complete macroscopic and microscopic resection without violating oncologic principles is paramount. Marulli et al. 12 recently described a multicenter European experience of patients undergoing robotic thymectomy for early-stage thymoma. All patients had Masaoka stage I or II tumors and, despite a range of diameters from 1 to 12 cm, demonstrated a 5-year survival rate of 90%.




Robotic Training and Accreditation



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Currently, much like with VATS thymectomy, there are no established guidelines for the training and accreditation of surgeons and operating room teams for performance of robotic thoracic procedures. As a result, each hospital center has developed its own policies regarding the credentialing of individual practitioners. Most uniformly mandate that surgeons attend an intensive, 2-day training course given by Intuitive Surgical® that is comprised of didactic instruction regarding the system components followed by simulation training for basic skills and cadaver-based training for specific procedures. It is critical for specialty-specific personnel, including operating room nurses, surgical technicians and bedside assistants, to be formally trained on the basics of system functioning, instrument changes, and position of the surgical cart. This is typically done by the robotic company representative. It is common, but not required for the prospective robotic surgeon to observe an established practitioner in order to become familiar with specific index procedures. This author cannot stress enough how critically important case observation is during training and prior to implementing robotics into the treatment of patients.



Once the entire surgical team has received the appropriate training, institutions usually will allow implementation of the robotic system into procedures under the supervision and guidance of a case proctor, defined as a surgeon with documented clinical experience independently performing robotic procedures. The console surgeon is typically required to perform 3 to 10 proctored cases before being granted independent robotic procedure privileges. Some hospitals require that eligible proctors themselves have performed a minimum number of cases, while the majority has no such requirement. In fact, most institutions do not mandate that the proctor be specialty-specific. Thus, a robotic urologist may proctor a thoracic surgeon. While this may be in compliance with a specific institutional requirement, this type of implementation is ill-advised. The ideal situation is for the training surgeon to observe an experienced robotic surgeon in their respective field and then enlist that individual, if possible, to serve as the case proctor. This maximizes the continuity of training and, consequently, patient safety during clinical implementation.




Patient Selection and Preoperative Assessment



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Mg With Or Without Thymoma


It is well accepted that thymectomy is most effective in younger patients with generalized MG with the goal of symptom improvement, decreased medication requirement, and for some, complete remission. Its role in patients with pure ocular MG or late onset of disease is less clear as ocular MG typically has a better overall prognosis and is less likely to resolve following thymectomy. However, up to 70% of patients who present with ocular symptoms only eventually progress to more generalized disease. Thus, in this patient population, the emphasis must be placed on prevention of disease progression. Patients with generalized disease diagnosed at an older age should be counseled about the realistic chances of benefit from thymectomy because even minimally invasive approaches can have long-term adverse effects.



The extent and severity of muscle weakness should be carefully elicited and documented. Patients should see their neurologist preoperatively for optimization of their medical treatment. In patients with severe weakness, preoperative treatment with either plasmapheresis or intravenous immunoglobulin therapy may be required. Patients should be prepared for the possibility of postoperative mechanical ventilation and myasthenic crisis. It is critical for the neurologist, anesthesiologist, and surgical team to work closely to achieve the best results. Recent imaging of the chest is advised preoperatively as 25% of patients with MG will have a concomitant thymoma. Although a computed tomography (CT) of the chest with intravenous contrast is preferred, magnetic resonance imaging (MRI) with and without contrast is also suitable.



Thymoma


Patients with known or suspected thymoma should undergo a recent CT chest with intravenous contrast to ascertain the size and extent of the lesion (Fig. 167-1). Particular attention should be paid to the possibility of invasion of surrounding structures, such as the lung, pericardium, and phrenic nerves. In addition, it is important to note if the tumor is located predominantly on one side or centrally as this may determine from which side the procedure will be approached. Careful assessment in the history and physical examination should be directed at eliciting any suspicion of undetected MG, as one-quarter of patients with newly diagnosed thymoma will have concomitant MG. As with any new surgical technique or approach, careful selection of initial cases is critical to success and progression. While scenarios such as large (>5 cm) tumors and/or those with suspected gross invasion of the thymic capsule into surrounding structures or prior sternotomy do not absolutely preclude a robotic approach, it is wise to avoid these conditions until a sufficient experience has been developed with the most straightforward cases. Informed consent for the use of robotic assistance should be obtained as a distinct portion of the procedure.

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Dec 30, 2018 | Posted by in VASCULAR SURGERY | Comments Off on Robotics: Thymectomy
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