John C. Kucharczuk
INDICATIONS/CONTRAINDICATIONS
Controversy surrounds the selection of the surgical approach to thymectomy. Clearly, the emergence and refinement of minimally invasive procedures has challenged the routine application of transsternal thymectomy. Patients with nonthymomatous myasthenia gravis likely benefit from a minimally invasive approach as long as the resection is complete. Similarly, patients with small, well-encapsulated thymomas are likely good candidates for minimally invasive approaches. In our current practice patients with large (>5 cm), well-encapsulated thymomas, patients with clearly invasive lesions who are pretreated with chemotherapy, and all patients with thymic carcinoma undergo a transsternal thymectomy. Figure 28.1 shows the pre- and post-treatment images of a patient who is offered a transsternal resection. This approach allows for easy resection of concomitant involved structures such as lung, chest wall as well as major vascular structures requiring resection and possible reconstruction. Table 28.1summarizes our current approach to thymectomy based on the clinical situation.
There are no major contraindications to transsternal thymectomy. In patients with prior cardiac surgery it is important to know the route of any coronary grafts and their proximity to the inner table of the sternum and the thymoma. These patients should be approached in the same way one would approach a redo sternotomy for cardiac surgery. The graft location should be mapped out preoperatively with either coronary catheterization or CT angiogram. I prefer CT angiogram. The sternum must be opened carefully to avoid damage to any underlying patent grafts. Cardiopulmonary bypass should be available and a plan must be in place should replacement of coronary graft be required either due to injury opening the sternum or due to tumor involvement.
Patients with pectus excavatum can present a challenge. In my experience I have performed transsternal thymectomy with no attempt to repair the pectus resulting in satisfactory outcomes. The lack of working domain makes minimally invasive approaches difficult in these cases although some have reported sternal lift type procedures, which may be applicable and may allow for adequate working domain.
Figure 28.1 CT scan of the chest showing a patient with a thymic carcinoma. A: Shows the initial presenting scan and (B) shows the postchemotherapy scan. The patient subsequently underwent complete resection including partial resection of the sternum and right anterior chest wall. He was reconstructed with a combination of mesh and methylmethacrylate, which was covered with a pedicled muscle flap.
PREOPERATIVE PLANNING
All patients should have a CT scan with intravenous contrast. With large, poorly encapsulated lesions suggestive of invasive thymoma or thymic carcinoma the patient undergoes a preoperative biopsy either by CT-guided needle biopsy or by anterior mediastinotomy (Chamberlain procedure) followed by preoperative chemotherapy. Following chemotherapy treatment patients undergo repeat enhanced CT scan prior to definitive resection for planning purposes. In these situations attention is focused on the possible need for vascular reconstruction.
If not already performed we also obtain acetylcholinesterase antibodies in all patients undergoing thymectomy. These tests can be helpful in uncovering patients with impeding myasthenia gravis despite noticeable symptoms. As part of the preoperative discussion we always inform patients that a percentage of patients with thymoma and no symptoms of myasthenia gravis may develop the disease later in life.
TABLE 28.1 Current Surgical Approach to Thymoma Based on Clinical Scenario
Clinically, many large thymomas are “phrenotropic.” Although most, none myasthenic patients can tolerate a neuropraxia or paralysis of a single phrenic nerve, this can have catastrophic effects in the myasthenic patient. The possibility of phrenic nerve injury should be discussed with all patients undergoing thymectomy by any approach.
Patients undergo preoperative pulmonary function testing. In myasthenia patients these serve as a base line; following the force vital capacity postoperatively to ensure adequate muscle strength for unassisted respiration.
As mentioned above, patients with prior coronary artery bypass surgery undergo graft mapping to determine the location and patency of each graft. Completely occluded grafts, which are involved with an invasive thymoma or thymic carcinoma, can be sacrificed. Patient grafts coursing through or inseparable from the thymoma must be bypassed.
SURGERY
The patient is brought to the operating room receives routine prophylactic antibiotics and preinduction subcutaneous heparin for DVT prophylaxis. For myasthenic patients the anesthesia team, surgical team, and nursing team review the list of contraindicated drugs in the preoperative meeting to assure they are not administered during or after the case. General anesthesia is administered and the patient is intubated with a left-sided double-lumen endotracheal tube. The tube is positioned for isolated lung ventilation with the help of a pediatric bronchoscope to allow for lung isolation if required during the resection.
Positioning
The patient is placed in a supine position with the arms tucked at the sides. A roll is placed length wise under the shoulder blades to extent the neck and drop the shoulders. For particularly large difficult lesions and for those patients with prior sternotomy the groins are prepped into the field and additional arterial or venous access should be acquired. When the lesion appears to involve the superior vena cava, caval atrial junction, or the innominate vein I always place intravenous access above and below the diaphragm, so that intravenous medication can be administered during times of intermittent caval clamping. For complex caval reconstruction, which requires more than a side-biting caval clamp with partial occlusion or a short complete clamping caval–atrial bypass, should be considered to avoid cerebral congestion due to venous outflow occlusion.
For lesions abutting the innominate artery, I usually place a right radial arterial line and a femoral arterial line to allow for monitoring of arterial blood pressure during innominate arterial reconstruction. The right radial arterial wave can also help document reestablishment of flow through and adequate reconstruction.
Technique
The chest is depilated with an electric clipper. The skin is prepared with 3M DuraPrep Surgical solution (iodine povacrylex and isopropyl alcohol) patient preoperative skin preparation. The drapes are applied. A midline sternal skin incision is made from the Angle of Louis to just above the tip of the xiphoid. Electrocautery is used to achieve hemostasis and the midline of the sternum is scored. An army-navy retractor is used to retract the skin and soft tissue in a cephalad direction above the sternal notch. The sternal notch is developed with electrocautery and finger dissection to develop a pathway above the suprasternal ligament. The midline of the sternum is found by palpation and the periosteum of the sternal midline is scored with cautery. Ventilation is temporarily suspended and the sternum is opened in the midline with a sternal saw. Upward lifting on the sternal saw minimizes the risk of injury to the pleura and underlying mediastinal structures. Once the sternum is open, electrocautery is used to achieve hemostasis along the inner and outer bony tables of the sternum. I avoid the application of bone wax or any other foreign material to achieve hemostasis.
Sternotomy for resection of a mediastinal mass after prior cardiac surgery presents requires special attention. First and foremost is to be sure that the target lesion is a thymoma and not a pseudoaneurysm from prior surgery; with modern imaging and preoperative biopsy techniques this confusion should not occur. The techniques for redo sternotomy are well described in the cardiac surgery literature. The major tenants of redo sternotomy are the avoidance of injury to mediastinal structure directly underneath the sternum and the complete resection of the thymic mass. Cardiac bypass is immediately available for these cases and in particularly difficult cases the arterial and venous groin cannula are placed prior to any attempt at opening the sternum. The previous sternal wires are left in place as a depth guide and an oscillating saw is used. The final inner table of the sternum is opened below with a heavy scissors. In these complex cases it is probably best to have a joint surgical team including an experienced thymic surgeon and a cardiac surgeon skilled at redo operations.
Once the sternum is open and the retractors are placed attention is turned toward resection. I start my dissection as inferiorly as possible; usually at the right inferior pole, sweeping up all the mediastinal contents with the dissection just superficial to the plane of the pericardium. Laterally, the dissection extends out to the pleural envelope. I avoid dissection around the main lesion and division involved structures until the final step in the procedure. Next I identify the innominate vein. If the vein is involved and requires resection, this is left for later in the procedure and we continue on to dissect out the cervical poles of the thymus. The cervical poles are followed up to their distal extent in the neck and tagged with silk sutures for retraction both for later pathologic orientation and for intraoperative retraction.
Finally, I turn my attention to the main lesion and the surrounding structure. If the lesion is adherent to the pericardium, no attempt is made at separation. A wide en bloc resection of the pericardium is performed. The pericardium is not reconstructed. In cases involving the innominate vein, the vein is generally divided with vascular staplers proximal and distal to the lesion with vascular staplers. No attempt at repair is made, accepting some postoperative upper extremity swelling, which responds to elevation and usually resolves as collateral venous pathways open. Innominate arterial involvement with resection is best reconstructed. A prosthetic ringed graft is used.
Superior vena cava involvement requires special mention. Although clamping of a partially occluded SVC is usually well tolerated, prolong complete clamping may cause intracranial edema and bleeding due to increased cerebral venous pressure. The increase in pressure is evident by the cyanotic facies patients develop under the drapes. Rapid clamping can also cause cardiovascular collapse due to acute decreased venous return to the right heart. Working closely with the anesthesia team, fluid administration and vasoconstrictive agents are used to increase the mean arterial blood pressure and normalized the brain arterial venous pressure gradient. The surgical team should also have a low threshold for intraoperative shunting or veno–veno bypass during particularly complex or lengthy reconstruction. Figure 28.2shows the CT scan of a patient with an invasive thymoma following preoperative chemotherapy who required atrial–caval reconstruction at the time of resection.
Figure 28.2 Post chemotherapy, presurgical CT scan showing invasion into the superior vena cava, which extended down to the level of the right atrium.
Figure 28.3 Post chemotherapy, presurgical CT scan showing an invasive thymoma with phrenic nerve involvement. A: The scout films show elevation of the left diaphragm consistent with phrenic nerve paralysis, (B) the axial image shows the primary lesion, which was completely removed via a transsternal approach including resection of the left phrenic nerve.
It is not uncommon for large invasive lesions to grow through the pleural envelope and into the adjacent lung. In most cases en bloc wedge resection with a generous gross margin is all that is required. Infrequently, a formal anatomic lung resection is required, which, nevertheless, can easily be performed from via the anterior approach through a sternotomy.
The phrenic nerves are at risk especially with large thymomas, which seem to have a predilection to abut, invade, and grow around the phrenic nerve. The most common place to injure the phrenic nerve is at the cephalad extent where it is in close proximity to the origin of the internal mammary arteries. To avoid injury I do not use electrocautery in these locations. When the thymic mass extends into the pleura at these locations I widely open the pleural space, locate the phrenic nerve lower in the chest, and follow it back up to the area of concern to avoid injury. The second most common location to injure the phrenic is lower down in the chest when the mass extends laterally over the pericardium. Often an intraoperative decision must be made as to whether or not to sacrifice the phrenic nerve or “peel” the lesion off the phrenic hoping that function will return. The decision is easier when the phrenic nerve is invaded by tumor, it is inseparable surgically and the diaphragm is paralyzed preoperatively as shown in Figure 28.3. I generally will sacrifice one phrenic nerve in a nonmyasthenic patient if I am confident that the resection will be complete. In patients with myasthenia I will not resect the phrenic nerve accepting a slightly higher risk of local recurrence. Instead I sharply dissect of the lesion sparing the nerve along its entire course. When the phrenic nerve is sacrificed, I do not perform diaphragmatic plication at the time of the sternotomy and I have not had any instance of patients requiring later plication. Consideration of nerve grafting is possible, but I have not had any experience with the application of these techniques.
Once the specimen is resected it is oriented for the pathology. The orientation is particularly important for postoperative radiation treatment should pathologic areas of invasion and/or positive surgical margins be confirmed microscopically. A photograph is generally taken as shown in Figure 28.4 utilizing either a hand-drawn background or a standardized mediastinal board for use in postresection treatment planning.
I open both pleural spaces and examine for unsuspected pleural drop metastasis. A single soft Blake drain is placed across the mediastinum crossing both pleural spaces. The sternum is closed with sternal wires and the remaining incision is closed in layers. The patient is extubated in the operating room and transported to our thoracic surgical unit for postoperative care.
Figure 28.4 Images show resected invasive thymomas following pretreatment with chemotherapy. The specimens are photograph for orientation and the pictures are placed in the patient’s electronic medical record should postoperative radiation planning be needed. A:Demonstrates a specimen, which included resected lung as well as the midportion of the innominate vein. It is oriented on a hand-drawn picture to document the associate with nearby structures. B: Demonstrates a specimen oriented on a standard medisatinal board.
POSTOPERATIVE MANAGEMENT
The mediastinal tube is placed to a Pleuravac drainage system. The tube is maintained on suction for 24 hours and then converted to water seal. Once the drainage tapers off the tube is removed, usually at 48 to 72 hours. Patients are generally discharged 24 hours following tube removal to allow for titration of pain medications. They are restricted from heavy lifting and twisting exercises and athletics for 6 weeks.
COMPLICATIONS
Complications are best divided into acute and long term. The most common acute complication is bleeding requiring reexploration. Fortunately this is rare especially in the absence of vascular reconstruction. Respiratory complications occur but can be avoided by very aggressive pulmonary physiotherapy and early ambulation, which is instituted on the morning following surgery. Special attention is required in the myasthenia patient who should be restarted on all preoperative medications especially mestinon and immunosuppression. Dose timing of these drugs can be critically important in the brittle myasthenic and a well-informed nursing staff is essential. A number of commonly administered drugs can initiate a myasthenic crisis. A current list of contraindicated medications in myasthenia is kept updated by the pharmacist on the thoracic surgical unit and reviewed with all house staff and nurses caring for these patients.
RESULTS
The results following transsternal resection of a large thymoma are driven by on the stage of disease and the completeness of resection. In early-stage disease with smaller lesions minimally invasive techniques probably provide similar outcomes to transsternal resection. In more advanced-stage disease with larger lesions, local invasion, and/or preoperative treatment the transsternal approach provides outstanding exposure with the opportunity to carry out a complete resection.
CONCLUSIONS
Thymectomy for nonthymomatous myasthenia is probably best approached through minimally invasive techniques (VATS, robotic, transcervical).
Thymectomy for small thymomas with or without myasthenia can be approached successfully with either minimally invasive techniques or a transsternal approach (full or partial sternotomy) with good results.
Patients with large thymomas (>6 cm), thymomas invading adjacent structures, and those pretreated with chemotherapy are probably best served by transsternal thymectomy.
Recommended References and Readings
Detterbeck FC, Moran C, Huang J, et al. Which way is up? Policies and procedures for surgeons and pathologists regarding resection specimens of thymic malignancy. J Thorac Oncol. 2011;6(7 suppl 3):S1730–S1738.
Hamdi S, Mercier O, Fadel E, et al. Is sacrificing the phrenic nerve during thymoma resection worthwhile? Eur J Cardiothorac Surg. 2014;45(5):e151–e155. doi: 10.1093/ejcts/ezu025. Epub 2014 Feb 23.
Huang J, Detterbeck F, Wang Z, et al. Standard outcome measures for thymic malignancies. J Thorac Oncol. 2010;5(12):2017–2023.
Manoly I, Whistance RN, Sreekumar R, et al. Early and mid-term outcomes of trans-sternal and video-assisted thoracoscopic surgery for thymoma. Eur J Cardiothorac Surg. 2014;45:e187–e193.
Ruffini E, Detterbeck F, Van Raemdonck D, et al. Thymic carcinoma: A cohort study of patients from the European society of thoracic surgeons database. J Thorac Oncol. 2014;9(4):541–548.