159: Thoracoscopic Approach to Thymectomy with Advice on Patients with Myasthenia Gravis

Thoracoscopy is the application of video imaging technology to standard thoracic surgical procedures. The thoracoscopic approach permits indirect visualization of the thoracic cavity without the necessity of performing a full thoracotomy. Before the current era, the standard surgical approach to thymectomy was through a midline sternotomy or a cervical collar incision. In the last two decades, however, thoracoscopic thymectomy has been used increasingly in selected patients as a means of reducing pain and recovery time while maintaining the quality of gland removal, as well as comparable remission and asymptomatic disease rates compared to other minimally invasive and open techniques.¹ Thoracoscopic thymectomy is a good alternative to standard surgical treatment with full sternotomy because it offers excellent visualization (superior to the collar incision) and avoids the morbidity of a sternal division. We enthusiastically advocate a thoracoscopic approach to myasthenia gravis (MG), thymic cysts, thymic masses, and other anterior mediastinal tumors, including small (<2 cm) thymomas.^2,3 Bulky thymomas may be better visualized through a standard sternotomy. In this chapter, we describe our technique for thoracoscopic thymectomy with particular advice on ensuring a complete resection.

For the purposes of this description, we will refer to the superior portions of the H-shaped thymus gland as the right or left cervical horns, and the inferior portions will be referred as the right or left lobes.

Thoracoscopic thymectomy is well tolerated by patients of any age or gender owing to the minimally invasive nature of this approach. The usual position for a thoracoscopic procedure is the lateral decubitus position. We have lately added slight cervical flexion to permit caudal migration of the cervical horns and easier dissection, which obviates the need for a cervical incision. This position permits adequate instrumentation of the chest and rapid conversion to open thoracotomy in the event of bleeding or extended re-section. The patient must be intubated with a double-lumen endotracheal tube for split-lung anesthesia to permit selective deflation of the right or left lung. A left-sided double-lumen endotracheal tube is preferred because it is safer and easier to intubate the left mainstem bronchus owing to its length. Most thoracoscopic procedures can be performed with three ports: one for the camera and two for instrument access. It is important to place the ports as far apart from each other as possible to provide opposing angles of access to the intrathoracic target. A camera with a 30-degree angled telescope is also recommended for better intrathoracic visualization. Ports that have been placed too close together prevent adequate countertension on the tissues and cause crowding of instruments. A baseball diamond analogy has been used to describe port placement.⁴ The camera is at home plate, and the instruments are at first and third base. The target lies between the pitcher's mound and second base. A fourth port can be added later in the procedure to improve exposure and retraction of the specimen. Blake drain is used unless undue air leak or drainage is noted then a single chest tube is preferred.

In the subset of patients with MG, onset of the disease is correlated with gender and age. MG tends to peak in the second and third decades of life for women versus the sixth and seventh decades for men. For women, early resection is associated with a better response. Thus the typical female patient is a young woman between 25 and 30 years of age who has generalized neuromuscular weakness and is seeking to diminish the consequences of lifelong steroid therapy. Since men experience later onset of disease and a greater incidence of thymoma, male patients usually are older than 55 years of age.

Routine preoperative studies include pulmonary function testing, a posteroanterior and lateral chest radiograph, and chest CT scan. The preoperative assessment of patients with MG is performed in collaboration with a team of specialists including the neurologist, anesthesiologist, thoracic surgeon, and pulmonologist. MG is an autoimmune disease resulting from the production of antibodies against the acetylcholine receptors of the neuromuscular synapse. For this reason, patients with severe MG or in crisis may undergo perioperative plasmapheresis or immunoglobulin administration which decreases the level of circulating antibodies.⁵ Often on long-term steroid therapy, patients with MG also may receive a steroid stress dose before surgery, with subsequent taper in the first postoperative week.

Several approaches to thoracoscopic thymectomy have been described, including right, left, bilateral, and bilateral with cervical incision. In general, we prefer to use the right thoracoscopic approach. It provides better visualization of the junction between the innominate vein and the superior vena cava, the so-called innominate–caval junction (ICJ), and thus a better view of the thymic veins. We have encountered more ease of dissection of the cervical horns by adding neck flexion, which permits caudad migration of the lower anterior neck structures. In addition, since the heart and pericardium are predominantly left-sided structures, there is less room on the left for maneuvering the thoracoscope and other surgical instruments.

Right Thoracoscopic Approach

Position

The patient is anesthetized and intubated with a single-lumen endotracheal tube. A flexible bronchoscope is passed through the lumen and down into the airway to assess for the presence of incidental intraluminal lesions or extrinsic compression. If the airway is clear, a double-lumen endotracheal tube is placed for split-lung ventilation, using the flexible bronchoscope to confirm its position. The mechanics of delivering anesthesia in thoracoscopic procedures are detailed in Chapter 5. It warrants mention, however, that muscle relaxants should be used cautiously in patients with MG, if at all, in view of the goal to withdraw the patient from ventilation as quickly as possible after the operation.

For the right thoracoscopic approach, the patient is placed in the left lateral decubitus position. A roll is placed under the patient's side, elevating the body by approximately 45 to 60 degrees. The easiest way to accomplish this position, we have found, is to place the patient in the full lateral decubitus position and then rotate the patient posteriorly by approximately 30 degrees. The right arm is elevated into a swimmer's position, and slight cervical flexion is achieved. The right chest is prepped and draped in the usual sterile fashion.

Port Placement

Three portals are created in a triangular configuration (Fig. 159-1). The first port (5–20 mm) is placed over the fifth intercostal space (ICS) between the anterior axillary and midaxillary lines. From this location, the chest tube exits the skin anterior to the superior iliac crest of the pelvis, thus preventing chest tube compression or kinking in the postoperative period. This port site is one ICS above the site that we generally use for thoracoscopic procedures of the posterior or midchest (i.e., sixth ICS) and permits use of the curved or straight Foerster (ring-hatched) forceps in the upper anterior mediastinum. The second port (5 mm) is placed in the fifth ICS between the mid- and posterior axillary lines, near the tip of the scapula. The third port (2 cm) is placed at the base of the axilla over the top of the third rib. The size of the ports may vary depending on surgical instrumentation and surgeon preference.

The camera is placed initially in the anterior fifth ICS port for exploration of the chest. We recommend a 30-degree 5-mm telescopic lens for easy visualization and dissection of the mediastinum. Ventilation is stopped on the right side. The entire thoracic cavity is examined to identify the surgical landmarks, namely, thymus gland, phrenic nerve, superior vena cava, and internal mammary vessels (Fig. 159-2). The posterior diaphragmatic sulcus is examined for “drop metastases.”

The camera is moved to the posterior fifth ICS port (5 mm) for the thymic dissection. This produces the classic dissection triangle with the surgeon standing posterior to the patient (Fig. 159-3). The left-hand instruments enter the axillary port, the right-hand instruments enter the anterior fifth ICS port, and the camera eye is between the left and right hands in the posterior fifth ICS port. A fourth port can be created at the surgeon's option and, if so, usually is placed caudally and later in the procedure to aid in dissection of the contralateral side. Placement is based on anatomic considerations, but a fourth port is often located in the seventh ICS in the midaxillary line.

While some surgeons recommend CO₂ insufflation to collapse the lung, we find that it is unnecessary for adequate atelectasis, and its use can compromise the patient physiologically.^6,7 Pneumomediastinum 24 hours in advance of surgery also has been reported as an aid to dissection, but we have no experience with this technique.⁸

For patients with MG, the more complete the anterior mediastinal resection, the better are the chances of improvement. Because of the embryologic origin of the thymus, ectopic thymic cells can be found in the parathymic fat and lower cervical pretracheal area. All anterior mediastinal tissue must be removed, including thymic tissue and pericardial fat pads from phrenic nerve to phrenic nerve (Fig. 159-4).

Mediastinal pleural cuts: The dissection begins from a posteroinferior position, just anterior to the phrenic nerve. We incise using scissors for the mediastinal pleura from the caudal end of the gland to just above the ICJ. A second cut is made in the mediastinal pleura just posterior to the internal mammary artery using cautery. These two pleural incisions come together just cephalad to the ICJ (Fig. 159-5).

Blunt dissection anterior/posterior: Blunt dissection of the mediastinal fat and thymic tissue is performed by developing the avascular plane posterior to the gland and anterior to the pericardium and, likewise, anterior to the gland and posterior to the sternum. This dissection is facilitated by removing the ipsilateral pericardial fat pad. The posterior plane is dissected first because the tissue attachments to the sternum, which suspend the gland anteriorly, assist in visualization of this dissection plane. Once all the parathymic fat has been dissected from the surrounding tissues, the right lobe of the thymus gland is exposed.

Ipsilateral cervical horn: We pull the right cervical horn down from the neck by broadly placing a Foerster forceps across the horn and pulling caudally. A second, ringed Foerster forceps permits a hand-over-hand technique. Electrocautery is used to cauterize the thymic branch from the inferior thyroid artery, which feeds into the thymus at the apex of each of the superior horns of the gland. The cervical horn then is bent back onto itself anteriorly and retracted to the left and caudad, exposing the innominate vein.

Thymic vein: With careful blunt dissection along the innominate vein, it is relatively easy to locate the thymic veins. The thymic veins, usually two or three, can be divided between endoclips. Once these vessels are ligated and divided, the area caudad to the innominate vein opens further with blunt dissection. The thymic tissue can be distinguished from parathymic fat best at this point in the procedure because it has been partially devascularized. Its color is deeper yellow or somewhat purple, and it has a firmer consistency, surrounded by a capsule.

Contralateral cervical horn: In the same blunt traction fashion, we dissect and mobilize the left cervical horn and cauterize the thymic artery entering at its tip. At this point, the suspensory ligament from the deep pericardium is freed using electrocautery. This completes the cephalad margin of dissection.

Blunt dissection of contralateral lobe and fat pad: The left lobe is retracted cephalad with right lateral direction. Blunt dissection frees the gland from the pericardium. A small portion of the left-sided parathymic fat is removed along with the surgical specimen, with care not to injure the left phrenic nerve. The specimen is placed in an Endobag and brought out through the axillary incision. The specimen is oriented for the pathologist, and areas of concern can be frozen to assess the margins. The mediastinum is irrigated, and hemostasis is confirmed. A Blake tube is placed posterior to the sternum through the anterior fifth ICS wound. The remaining ports are closed using two or three layers of absorbable suture.

Left Thoracoscopic Approach

Position

For a left thymectomy, the patient is placed in a 45- to 60-degree right lateral decubitus position with small rolls placed along the right scapula and behind the patient's hip, and cervical flexion is also warranted.⁹

Ports

The first port is placed in the fifth ICS on the anterior axillary line. The second port is placed between the posterior and midaxillary line in the fifth ICS near the tip of the scapula. The third port is placed at the base of the axillae over the third rib. The best location for the camera is in the posterior port between the left and right instrument ports, with the surgeon standing posteriorly.

Mediastinal pleural cuts: Once the ports have been placed and the mediastinal structures identified, dissection begins with the left thymic lobe. The mediastinal pleura is opened anterior to the phrenic nerve with scissors and posterior to the mammary vessels using cautery (Fig. 159-6).

Blunt dissection anterior/posterior: Blunt dissection is performed posterior and then anterior to the gland.

Ipsilateral cervical horn: Since the left cervical horn is displaced more posteriorly than the right horn because of the contour of the ascending aorta, this may limit the posterior dissection of the upper part of the gland until the left horn has been pulled down from the neck.

Thymic veins: The lateral extent of the innominate vein is usually hidden by mediastinal fat on the left. After the left pole has been dissected, the thymic veins are clipped and divided proximal to the thymus.

Contralateral cervical horn: The right phrenic nerve can be found lateral or just anterior to the superior vena cava. Visualization of this area is not as good from the left approach. This nerve could be injured from blunt traction if the clamps extend beyond the right lateral margin of the gland. Clear visualization and skeletonization of the right cervical horn avoid this injury by displacing the right horn in a posterocaudal manner and pushing the right mediastinal pleura off the right lateral side of the horn and then off the lateral side of the right lobe (Fig. 159-7). The most difficult portion of thymectomy from the left-sided approach is dissection at the ICJ.

The cava and innominate veins form a 120-degree angle at the ICJ, and blunt dissection with an endo-Kitner dissector through the lower anterior port hits this junction at a 45-degree angle (Fig. 159-8). This can lead to injury to one of these structures. Dissection from the upper axillary port tends to avoid this problem.

Blunt dissection of the contralateral lobe and fat pad: The surgeon grasps the right lobe with gentle traction toward the left side, dissecting it bluntly away from the left phrenic nerve.

During the last couple of years, we have begun using CO₂ insufflation in the chest. Insufflation is well tolerated to 10–12 cm H₂O. Ports have decreased in size (5 mm) and advanced dissection instrumentation (ultrasonic dissector) is preferred. This has enhanced our ability to extend into the cervical horns of the thymus. Using unilateral or bilateral approaches we have maximized the ectopic thymic tissue extra action with equal results to the open techniques.

Thoracic drainage is done with silastic tubes when needed and most uncomplicated VATS thymectomies are left without a drain nowadays.

The Blake drain or chest tube is removed when the effluent is serous and less than 100 mL/d, usually on the first postoperative day. Diet is resumed as tolerated on the first postoperative day. Pain is controlled with IV medications and with oral medication when oral intake is restored. Postoperative chest x-ray is obtained to ensure complete lung reexpansion. Mean postoperative hospital stay for thoracoscopic thymectomy patients has been reported to be 1.64 days (range 0–8 days).¹⁰ The patient is seen in clinic approximately 2 weeks after surgery.

Special considerations for patients with MG include early extubation, preferably before leaving the OR, and careful monitoring of ventilatory function. Before considering tracheal extubation, adequate respiratory function must be ensured. For example, if the patient can lift his or her head for 5 seconds or when the inspiratory force exceeds −25 cm H₂O, the patient can be extubated safely.

The most serious complications of thoracoscopic thymectomy include iatrogenic injury to the phrenic nerve, which can lead to phrenic nerve palsy and diaphragmatic paralysis. Thorough knowledge of the regional anatomy and meticulous technique, as detailed earlier, including alternating use of scissor (nerve) versus cautery (vessel) dissection, are the best protection against this sort of injury. Performing the thymectomy from a right approach whenever possible avoids the potential pitfalls of working in the crowded left chest. Other morbidities such as hemorrhage, infection, pneumothorax, pneumonia, failure to wean from the respirator, conversion to thoracotomy, pleural effusion requiring drainage, myocardial infarction, empyema, and pulmonary embolus are managed according to standard practice. In the event of conversion owing to bleeding, we recommend an axillary thoracotomy to control the event and complete the procedure with video-assisted technique.

Thoracoscopic thymectomy is an excellent alternative to standard surgical treatment with full sternotomy. Its benefits can be enumerated in terms of reduced morbidity and mortality, shorter postoperative recovery, and enhanced cosmesis resulting from avoidance of sternal division.¹¹ Lately, a retrospective analysis of 57 patients with MG that underwent right three port VATS thymectomy were followed up with strict Myasthenia Gravis Foundation of America (MGFA) Clinical Classification for a minimum of 12 months. The complete stable remission rate was 15% and 28%, for 3 and 5 years, respectively. The asymptomatic disease rate was 59% at 5 years, with a median follow-up of 32 months. This study shows right VATS thymectomy achieves comparable remission and asymptomatic disease rates to other minimally invasive and open techniques.¹ Adequate resection with excellent visualization can be achieved by thoracoscopic technique and meticulous attention to the regional anatomy.

All surgical approaches to thymectomy have strengths and weaknesses. Transcervical thymectomy allows for excellent visualization of the cephalad horns of the thymus gland, whereas thoracoscopic approaches offer better visualization of the intrathoracic thymic tissue. A potential limitation of all approaches is unrecognized or “ectopic” thymic tissue. Since the thymus gland is derived from the third pharyngeal pouch, just ventral to the inferior parathyroid gland, ectopic thymic tissue can be found anywhere along its descent into the chest.