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Thymectomy by Median Sternotomy

Cameron D. Wright, MD
Thymectomy by Median Sternotomy is a topic covered in the Pearson's General Thoracic.

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Introduction

The two primary indications for thymectomy are the treatment of patients with thymoma and the treatment of patients with myasthenia gravis (MG) without thymoma. A number of different methods have been described to remove the thymus gland, including transcervical-trans-sternal “maximal” thymectomy, extended trans-sternal thymectomy, classic transsternal thymectomy, transcervical thymectomy, video-assisted thoracoscopic (VATS) thymectomy and robotic-assisted thymectomy (RATS). Each approach has its pros and cons, but this chapter will focus on the traditional sternotomy approach to resection of the thymus and/or thymic tumor.

Myasthenia gravis patients referred for thymectomy require a careful preoperative neuromuscular evaluation prior to undergoing surgery. Preoperative planning is critical in patients with MG to avoid postoperative complications such as aspiration, respiratory failure or myasthenic crisis. Most patients are taking pyridostigmine (Mestinon), which normally is continued until the time of surgery. Patients may also be taking prednisone or other immunosuppressive medications and these should also be continued up until surgery. Spirometry preoperatively may help identify those patients at increased risk of having problems postoperatively. Patients with a vital capacity less than 2.9 liters, forced expiratory force less than 40 cm H2O, previous respiratory insufficiency secondary to MG, or a history of MG greater than 6 years should be considered as higher risk for postoperative difficulty [1],[2],[3]. Patients with significant bulbar or extra-bulbar weakness or who are identified preoperatively as high risk for respiratory complications may also benefit from either preoperative plasmapheresis or IV immunoglobulin (IVIG) therapy to optimize their status prior to surgery. Plasmapheresis typically is performed over three to five sessions performed every other day prior to surgery. Studies have shown a reproducible benefit to patients who have undergone plasmapheresis treatment [4],[5],[6]. IVIG also appears in studies to show a post-operative benefit for patients with MG undergoing thymectomy, but studies comparing IVIG therapy against plasmapheresis are difficult to interpret since there is a bias for the more symptomatic MG patients to receive plasmapheresis preoperatively [7]. In patients with more modest symptoms, IVIG and plasmapheresis appear to be comparable, with greater ease in treatment noted with IVIG therapy. IVIG treatment is given as a 400 mg/kg/day dose administered over three to five days [7].

The goal of thymectomy for either treatment of thymoma or management of MG is the complete removal of all thymic tissue. There is a proven oncologic benefit in thymoma patients of performing a complete resection of the tumor, as most studies demonstrate that a complete resection is the most important prognostic factor [8]. It would seem likely that performing a complete thymectomy is the safest way to ensure a complete tumor resection as well, although there is some controversy over whether total thymectomy is in fact required in patients with thymoma and no evidence of MG. In MG, studies appear to demonstrate a higher remission rate with complete removal of all thymic tissue [9],[10]. The most effective method of removing all thymic tissue, however, continues to remain controversial. Studies have demonstrated the presence of microscopic deposits of thymic tissue in pericardial fat overlying the heart, in the aortopulmonary window, and behind the innominate vein [11]. Based on this information, some surgeons believe that the presence of any amount of mediastinal fatty tissue left behind compromises the results of the operative procedure [12], and this might suggest that median sternotomy is the best approach. Whether this assumption is correct continues to be a source of debate.

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Introduction

The two primary indications for thymectomy are the treatment of patients with thymoma and the treatment of patients with myasthenia gravis (MG) without thymoma. A number of different methods have been described to remove the thymus gland, including transcervical-trans-sternal “maximal” thymectomy, extended trans-sternal thymectomy, classic transsternal thymectomy, transcervical thymectomy, video-assisted thoracoscopic (VATS) thymectomy and robotic-assisted thymectomy (RATS). Each approach has its pros and cons, but this chapter will focus on the traditional sternotomy approach to resection of the thymus and/or thymic tumor.

Myasthenia gravis patients referred for thymectomy require a careful preoperative neuromuscular evaluation prior to undergoing surgery. Preoperative planning is critical in patients with MG to avoid postoperative complications such as aspiration, respiratory failure or myasthenic crisis. Most patients are taking pyridostigmine (Mestinon), which normally is continued until the time of surgery. Patients may also be taking prednisone or other immunosuppressive medications and these should also be continued up until surgery. Spirometry preoperatively may help identify those patients at increased risk of having problems postoperatively. Patients with a vital capacity less than 2.9 liters, forced expiratory force less than 40 cm H2O, previous respiratory insufficiency secondary to MG, or a history of MG greater than 6 years should be considered as higher risk for postoperative difficulty [1],[2],[3]. Patients with significant bulbar or extra-bulbar weakness or who are identified preoperatively as high risk for respiratory complications may also benefit from either preoperative plasmapheresis or IV immunoglobulin (IVIG) therapy to optimize their status prior to surgery. Plasmapheresis typically is performed over three to five sessions performed every other day prior to surgery. Studies have shown a reproducible benefit to patients who have undergone plasmapheresis treatment [4],[5],[6]. IVIG also appears in studies to show a post-operative benefit for patients with MG undergoing thymectomy, but studies comparing IVIG therapy against plasmapheresis are difficult to interpret since there is a bias for the more symptomatic MG patients to receive plasmapheresis preoperatively [7]. In patients with more modest symptoms, IVIG and plasmapheresis appear to be comparable, with greater ease in treatment noted with IVIG therapy. IVIG treatment is given as a 400 mg/kg/day dose administered over three to five days [7].

The goal of thymectomy for either treatment of thymoma or management of MG is the complete removal of all thymic tissue. There is a proven oncologic benefit in thymoma patients of performing a complete resection of the tumor, as most studies demonstrate that a complete resection is the most important prognostic factor [8]. It would seem likely that performing a complete thymectomy is the safest way to ensure a complete tumor resection as well, although there is some controversy over whether total thymectomy is in fact required in patients with thymoma and no evidence of MG. In MG, studies appear to demonstrate a higher remission rate with complete removal of all thymic tissue [9],[10]. The most effective method of removing all thymic tissue, however, continues to remain controversial. Studies have demonstrated the presence of microscopic deposits of thymic tissue in pericardial fat overlying the heart, in the aortopulmonary window, and behind the innominate vein [11]. Based on this information, some surgeons believe that the presence of any amount of mediastinal fatty tissue left behind compromises the results of the operative procedure [12], and this might suggest that median sternotomy is the best approach. Whether this assumption is correct continues to be a source of debate.

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Last updated: September 13, 2020