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. Additionally, 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
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 45–60 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. The right chest is prepped and draped in the usual sterile fashion.
Three portals are created in a triangular configuration (Fig. 135-1). 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.
For right thoracoscopic thymectomy, the patient is in the left lateral decubitus position and elevated approximately 30 degrees by placing a roll under the patient's side. Three ports are placed in triangular configuration with the patient's arms in swimmer's position.
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. 135-2). The posterior diaphragmatic sulcus is examined for “drop metastases.”
Important mediastinal landmarks that are visible with the camera placed in the anterior fifth intercostal port.
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. 135-3). 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.
For thymic dissection, the camera is moved to the posterior fifth intercostal port.
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.2,3 Pneumomediastinum 24 hours in advance of surgery also has been reported as an aid to dissection, but we have no experience with this technique.4
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. 135-4).
Anatomy of the thymus gland with most likely sites of ectopic thymic tissue.
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. 135-5).
A. Two mediastinal pleural cuts are made and conjoined at the ICJ. B. The ipsilateral cervical horn is pulled down from the neck using two ringed Foerster forceps permitting hand-over-hand technique. C. The thymic veins, which lie along the innominate vein, are dissected bluntly.
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.
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
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.5
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.
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. 135-6).
Initial mediastinal pleural cuts are indicated (dashed line) for a left thoracoscopic thymectomy. For this approach, the patient is in the right lateral decubitus position.
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.
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. 135-7). The most difficult portion of thymectomy from the left-sided approach is dissection at the ICJ.
Thymic dissection from a left-sided approach is more difficult owing to the necessity of circumnavigating the ICJ. A. Dashed lines indicate the ICJ, which lies below the “aortic” horizon. B. Injury of the right phrenic nerve is also more risky from a left-sided approach, especially when dissecting the contralateral (right) cervical horn. Visualization is improved by displacing the right horn posterocaudally and pushing the mediastinal pleura gently off both sides of the right horn.
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. 135-8). This can lead to injury to one of these structures. Dissection from the upper axillary port tends to avoid this problem.
The junction between the innominate vein and superior vena cava (ICJ) is encountered when operating from the lower port on the left side. Approaching the dissection through the upper axillary port is recommended 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.