167: Robotics: Thymectomy

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.^7–10

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.

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%.

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.

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.

All patients considered for thymectomy should have adequate cardiopulmonary and performance status to tolerate single-lung ventilation and possible intrathoracic CO₂ insufflation. Patients with significant smoking history, diminished exercise tolerance or a history of chronic obstructive pulmonary disease should probably undergo preoperative pulmonary function testing. Smoking cessation for active smokers should be aggressively advocated.

Preparation of the Robot

The operating room technical staff sets up the robotic surgical system (surgical cart, surgeon's console, vision system) in the room (Fig. 167-2). In the beginning of the case, the nursing staff power up the system, run the appropriate diagnostics, and drape the robotic arms and camera. This requires two individuals and typically takes 5 to 10 minutes for staff who are trained and familiar with the process and occurs prior to or while the patient is undergoing induction of anesthesia and positioning.

Anesthesia Considerations and Patient Positioning

Standard methods of induction of general anesthesia and endotracheal intubation are used. Single-lung ventilation via either double-lumen endotracheal tube placement or bronchial blocker, while not mandatory, greatly facilitates the procedure and can be initiated early once correct tube position has been verified bronchoscopically or clinically. Patients with MG are exquisitely sensitive to nondepolarizing muscle relaxants, and their use should be avoided as much as possible. Anesthesia can be maintained with volatile, inhalational agents. If muscle relaxation is necessary, a reduced dose of intermediate-acting nondepolarizing agents can be employed at the beginning of the procedure.

The patient is placed in a supine position with the ipsilateral side elevated 30 degrees with a gel roll or padding placed longitudinally below the tip of the scapula. The contralateral arm is padded and tucked. The ipsilateral arm should be slightly abducted, padded and placed on an armboard that is fully adducted in line with the operating room table so that the arm and shoulder are below the anterior chest. The operating table is moved away from the anesthesia machine and angled with the foot of the table away from the surgical cart. This establishes enough space to dock the robot which will be positioned at the contralateral side. Thus, with a left-sided robotic approach, the left side of the patient is elevated with the robotic cart docked from the right side of the table. Care must be taken to insure that sufficient length of the circuit tubing is available during this positioning, and the anesthesia team must be comfortable that there is adequate access to the patient's airway once docking of the robotic system has taken place. The entire neck and chest below the xiphoid process should be prepped and draped in the event that a transsternal or contralateral incision is needed.

Initial Exploration and Docking of the Robot

Robotic thymectomy is a three-incision, three-arm procedure. Initial thoracic exploration is conducted with the robotic thoracoscope through a 12-mm port in the fifth or sixth intercostal space (ICS) in the anterior axillary line. Use of CO₂ insufflation to 8 to 10 mm Hg is generally well tolerated and enhances the visualization and working space by increasing the anteroposterior diameter of the chest. The anesthesia team should be alerted to the initiation of insufflations so that they may monitor the patient's airway and blood pressure. When operating on the left side, care must be taken in making this initial incision as it will be quite close to the pericardium. The camera port should be placed without the use of a sharp trocar and CO₂ insufflation should be initiated prior to placing the subsequent ports.

The remaining ports are 8 mm reusable metal robotic ports placed under robotic thoracoscopic visualization. Because the working space is limited, it is critical to space the ports at least one handbreadth apart to avoid arm collisions that will limit full range of motion of the instruments in the chest. The second port is placed in the sixth or seventh ICS in the inframammary crease in the midclavicular line. The last port is placed in the third or fourth ICS anterior to the anterior axillary line. Once all three ports have been placed, the surgical cart is brought into position from the contralateral side with the center column and camera arm in a line between the camera port and the contralateral shoulder. It is important to position the arms within the working range and avoid having them too close to the ports and the patient as this will limit the working range of the instruments.

Once the surgical cart is in position, the camera arm is attached first to the 12-mm port. The camera arm and port are used to elevate the anterior chest wall for increased visualization. The robotic thoracoscope is introduced and secured to the camera arm. A 0-degree scope is preferred for the initial dissection and avoids excessive torque in the interspace. The remaining ports are attached to the robotic arms, and the surgical instruments are introduced under direct thoracoscopic vision. A Cadiere forceps is most commonly controlled by one hand for grasping tissue, and a cutting instrument (monopolar spatula, Maryland bipolar, monopolar hook) is used in the other hand. After the instruments have been introduced, the operating surgeon moves to the surgeon's console. The first assistant remains at the table and performs instrument exchanges as needed. A separate, nonrobotic assistant port is typically not required.

Thymectomy

Dissection is initiated by incising the mediastinal pleural medial to the phrenic nerve. It is easiest to begin in the midpoint of the pericardium where fat content is lowest. The perithymic and pericardial fat is mobilized along the entire length of the phrenic nerve from cephalad to caudad off of the pericardium as far toward the contralateral chest as is convenient. CO₂ insufflation greatly facilitates dissection once the mediastinal pleural is divided. Dissection at the ipsilateral anterior diaphragmatic recess can be limited by instrument conflict. It often helps in this situation to retract with the superior instrument arm and divide the tissue with the inferior arm.

Next, the mediastinal pleural just posterior to the posterior table of the sternum is incised from the thoracic inlet to the diaphragm and from the ipsilateral to the contralateral pleural space. The contralateral pleura is divided completely, allowing dissection up to the contralateral phrenic and for greater manipulation of the specimen as the mobilization proceeds. The dissection continues cephalad and toward the contralateral pleural space by dividing en bloc all attachments of the specimen to the pericardium. Visualization of tissue at the limits of the contralateral pleural space is improved through the use of the 30-degree robotic thoracoscope.

Once the majority of the specimen has been mobilized off the pericardium toward the neck, the ipsilateral portion of the innominate vein is identified. The superior horns are bluntly separated from the innominate vein. The thymic veins are isolated and divided either by serial clips or through the use of the robotic harmonic scalpel. Similarly, the superior horns are freed from the surrounding attachments, pulled inferior out of the neck and either clipped and divided or resected by harmonic scalpel. It is useful to place a clip of one of the horns for proper orientation of the specimen once ex vivo. Visualization can be improved by allowing the already mobilized portion to fall into the contralateral pleural space. After all of the tissue from the thoracic inlet has been freed, the remaining attachments to the anterior surface of the pericardium medial to the contralateral phrenic should be divided. At this point, if not done so previously, a change to the 30-degree thoracoscope in a downward orientation will facilitate identification and avoidance of the phrenic nerve.

Specimen Removal

Once the entire gland and surrounding tissue have been completely mobilized, the inferior port may be removed. Removing the specimen from this incision is preferable because the rib space is widest in the anterior position. When the thymoma or other thymic mass is larger than the initial incision, the incision should be enlarged with an Anchor™ tissue retrieval bag (Anchor Products Company, Addison, Illinois) or other suitable bag is placed through it to retrieve the specimen. A durable nylon bag is preferred to plastic to minimize the chance of rupture and spillage. A conventional thoracoscopic grasper can be introduced in the superior port manually and used to grasp the specimen. The sac should be positioned such that the full extent of the bag may be opened toward the contralateral chest. Once the specimen is placed into the bag, it is removed (Fig. 167-3).

Termination of the Procedure

After the specimen has been removed, the operative bed should be inspected for any signs of active or potential bleeding. Any blood or clots should be irrigated and removed. The ports are then removed, and a single chest tube is placed through the camera incision and positioned with the tip at the apex of the ipsilateral chest or in the anterior mediastinum. The lung should be reinflated under direct thoracoscopic vision with the robotic scope placed in the inferior incision. The remaining wounds are closed in a standard fashion.

Standard postoperative management should be undertaken. In virtually all cases, patients can be extubated in the operating room and brought initially to the postanesthesia care unit. The chest tube may be left to water seal. Patient-controlled analgesia should be initiated through the use of a preoperatively placed epidural or a peripheral narcotic combined with intraoperative intercostals blocks. Patients may be transferred to a surgical floor with telemetry. If the immediate postoperative chest radiograph shows no evidence of pneumothorax or effusion, and there is no air leak, the chest tube may be removed immediately. Chest physiotherapy and early ambulation should be provided and encouraged. In patients with MG, their preoperative medications should be resumed and regular checks of oxygen saturation and incentive spirometry should be performed for early detection of respiratory muscle weakness. Commonly, patients can be discharged the following day provided there are no other concomitant complications; and pain control on oral medication is sufficient.

Potential intraoperative and postoperative complications are no different with a robotic approach to thymectomy than VATS or transsternal thymectomy. However, there are unique aspects to robotic thoracic procedures and thymectomy that need to be considered.

1. Lack of tactile feedback: The robotic arms do not impart haptic feedback to the console (operating) surgeon. Therefore, both the console surgeon and the bedside assistant must be constantly vigilant about inadvertent injury to either the external patient or surrounding internal structures by the instrument arms or the instruments themselves. Externally, care must be taken to insure that the arms do not compress any part of the patient with undue force or for a prolonged period of time. Internally, the surgeon must pay close attention to the visual feedback to prevent direct traction injury and compression injury by the shaft or heel of the instruments to adjacent structures.

2. Visual magnification: The robotic thoracoscope by design has greater magnification compared with the optics of the conventional camera. This is quite beneficial when working in a narrow, confined space, but results in decreased overall perspective view. This can be a disadvantage in the chest when one is attempting to delineate anatomic boundaries. It is critical to zoom out to the farthest extent possible when a greater overall view is required.

3. Hemorrhage: While the threat of hemorrhage during thymectomy is not unique to robotic procedures, absence of the operating surgeon at the bedside for immediate intervention is a necessary condition of the current master–slave robotic system. There are several strategies to maximize safety and minimize patient morbidity in the event of significant vascular injury. First, anticipation of a potential injury and maintaining a low threshold for conversion is key. Second, there must be a sponge stick ready and available for the bedside assistant to use for temporary tamponade of a bleeding vessel. Third, the bedside staff must be poised for rapid instrument removal and undocking of the surgical cart in preparation for conversion. With proper training, this can be executed in less than 1 minute, and use of robotic technology should never impede timely management of potentially catastrophic bleeding.

4. Right or left-sided approach: Robotic thymectomy is typically performed from a unilateral approach, and there is much debate regarding the optimal side from which robotic thymectomy should be approached. Advocates of a right-sided approach feel that there is initially more room to safely place the ports and initiate dissection. In addition, identification of the innominate vein from the right is technically easier than from the left. The main weakness of a right-sided approach is that the left phrenic nerve is more difficult to visualize, particularly near the thoracic inlet. Proponents of a left-sided approach feel that identification of the right phrenic is easier, as is dissection high into the neck. The innominate vein, however, is more difficult to identify from the left, and the pericardium is very close to the chest wall during initial exploration and docking. Most agree, however, that in the case of a mass that is predominantly located on one side, the thymectomy should be approach from the same side as the mass.

5. No touch technique: Robotic thymectomy, particularly in the setting of a known or suspected thymoma, should be conducted with a no-touch technique with respect to both the thymic tissue and the lesion, if present, to avoid seeding of the anterior mediastinum and pleural spaces with either tumor or retained thymic tissue. This is particularly important with respect to robotic technology where there is no haptic feedback. Thus, during active retraction, it is critical to grab only perithymic tissue. As the specimen becomes more mobilized and especially when a mass is involved, a better strategy is to use the closed instrument to push rather than grab the specimen. If adequate retraction and exposure cannot be accomplished without increased risk of tearing and spillage, conversion to a transsternal approach should be considered.

Robotic thymectomy is a safe and feasible method of accomplishing complete thymectomy for surgical treatment of MG and thymic neoplasms. The 3D high-definition visual system and wristed instrumentation are ideal for the anterior mediastinum. The procedure can be performed with minimal morbidity and an expected hospital stay of just 1 to 2 days. As with any procedure, patient selection, preoperative preparation, and multidisciplinary care are critical for success.

The risks and benefits of robotic thymectomy are outlined. The “insider's” tips as to how to do this better are important for anyone new to robotic surgery.