Transcervical Thymectomy
Smit Singla
Joseph B. Shrager
Transcervical thymectomy (TCT) was developed primarily for excision of the thymus gland in patients suffering from myasthenia gravis (MG). A relationship between MG and the thymus gland was first proposed by Oppenheim in 1889 and Weigert in 1901, both of whom described thymic tumors at autopsy in patients with MG.37,49 The advent of chest radiography in the first half of the twentieth century provided further evidence that MG was associated with enlargement of the thymus gland in the anterior mediastinum.
In 1911, Sauerbruch40 performed the first operation for MG. Using a transcervical approach, he successfully removed a 49-g hyperplastic thymus gland from a young woman, with subsequent control of her symptoms. This operation appears to have been largely an isolated event. However, a new era for thymic surgery began at Johns Hopkins when Blalock,5,25 in 1939, reported successful removal of a thymic tumor via a median sternotomy (MS), with a favorable effect upon the associated MG. The patient’s symptoms resolved slowly and she remained asymptomatic for many years. Blalock popularized thymectomy for nonthymomatous MG, reporting in 1944 a series of 20 patients with similar results.3,4 With this demonstration, interest in surgery of the thymus gland grew rapidly, along with controversy regarding the best means of approaching the gland.
The history of the transcervical approach to the anterior mediastinum begins with Ludwig Rehn of Frankfurt, Germany. In 1896, he performed a transcervical approach to fix an anterior mediastinal mass to the posterior manubrium.26 Sixty years later, using the same principle, Papatestas38 popularized the transcervical approach to the thymus gland. In 1987, he published data collected over the previous 30 years. His technique of TCT was carried out without a self-retaining, sternum-lifting retractor and largely by blind, blunt dissection into the anterior mediastinum. It is likely that this approach rarely led to a total thymectomy. He argued, however, that the approach had significant advantages over sternotomy, and he advocated it for all patients with MG.
During this period MS became the most widely accepted approach to thymectomy in MG. The rationales for a transsternal approach and other even more extensive procedures, including “maximal transsternal and transcervical thymectomy,” were described best by Jaretzki and colleagues.21,23 These authors emphasized, first, the carefully documented presence of nests of thymic tissue outside the thymic capsule in the mediastinal and cervical fat in autopsy studies in a high percentage of patients. They argued that it was unlikely that this tissue would be resected by a limited transcervical approach. Second, they emphasized the occasional cases of complete remission from MG after removal of residual thymic tissue after a failed initial thymectomy. They, therefore, emphasized the importance of removing even small extrathymic nests of tissue at operation.
The development of a sternum-lifting retractor by Joel Cooper in 1988 dramatically improved the visualization of the thymus gland via the neck, converting a largely blind procedure into one that allows good visualization of the entire anterior mediastinum and dissection of the thymus from surrounding structures under direct vision. This operation, termed “extended TCT” by Cooper,11 allowed a far more complete resection of thymic tissue than had previously been possible through a cervical incision, and the results published by his group and others (including the authors) repopularized the transcervical approach to the gland.6,42 In the last decade of the twentieth century, other minimally invasive approaches to the thymus gland—various video-assisted thoracoscopic (VATS) approaches—were also advocated and gained some popularity.30 There certainly remains significant controversy regarding the ideal surgical approach for thymectomy in MG.
For reasons that are described further below, the authors believe that extended TCT has certain advantages over each of the other approaches, and there is no doubt that it has become a well-accepted approach in patients with nonthymomatous MG.10,43
In any discussion of thymectomy for MG, it is important to note that there has never been a randomized trial establishing the added benefit of thymectomy over medical therapy alone. Many believe that most of the published retrospective studies support a role for thymectomy in the management of this disease, but no level 1 evidence on the issue exists.
Anatomic Considerations
The thymus gland is a flattened bilobed structure residing in the anterior mediastinum overlying the pericardium and the great vessels. The two lobes fuse at the gland’s midportion, making an H-shaped structure. The two upper horns extend into the neck, generally passing over the innominate vein and joining the thyroid gland by the thyrothymic ligaments. The lower horns lie on the pericardium and attach to the pericardial fat pad. Although the body of the gland contains over 95% of the functioning thymic tissue, aberrant nests of thymic tissue have also been reported at multiple locations within the chest cavity. Masaoka and Fukai31,16 found that nearly 70% of their patients had
microscopic collections of thymic tissue in the mediastinal fat separate from the main, intracapsular gland. Jaretzki and Wolff,23 in 1988, not only reported similar rates of mediastinal extracapsular thymic tissue but also noted that approximately one-third of patients had ectopic thymus in the fatty tissues of the neck. The clinical and physiologic significance of these extracapsular nests—for example, whether their resection is important—remains controversial.
microscopic collections of thymic tissue in the mediastinal fat separate from the main, intracapsular gland. Jaretzki and Wolff,23 in 1988, not only reported similar rates of mediastinal extracapsular thymic tissue but also noted that approximately one-third of patients had ectopic thymus in the fatty tissues of the neck. The clinical and physiologic significance of these extracapsular nests—for example, whether their resection is important—remains controversial.
The thymus gland receives its arterial supply superiorly via branches of the inferior thyroid artery, laterally via branches of the internal mammary arteries, and inferiorly via the pericardiophrenic branches. The predominant venous drainage of the gland is via central branches draining from the undersurface of the gland into the left innominate vein and via small veins that accompany the arterial supply.
The thymus lies close to the two phrenic nerves at the level of the thoracic inlet, becoming intimate with these at its middle portion as the two nerves descend from the neck into the chest. This relationship is obviously of great surgical importance. Whereas the upper poles of the gland usually pass anterior to the left innominate vein, the phrenics invariably pass posterior to the vein.
The thymus gland weighs approximately 15 g in a newborn and grows until puberty to reach a maximum weight of nearly 40 g. It involutes thereafter and persists in an atrophic state into old age, although in patients with MG and thymic hyperplasia it may be as large as in adolescence.
Indication for Thymectomy in Myasthenia Gravis
The indication for thymectomy in patients with MG has been a topic of sustained discussion. Numerous nonrandomized studies have shown improvement in myasthenic symptoms in 60% to 100% of patients and drug-free complete remission in 19% to 50% of patients after thymectomy.29,20 This can be contrasted with historical complete remission rates in medically treated patients that seem far lower. An American Academy of Neurology practice parameter published in 2000,17 however, recommends thymectomy only “as an option” to increase the probability of remission or improvement for patients with MG.
This important evidence-based review17 focused on the 21 controlled studies comparing MG patients undergoing thymectomy with those treated medically. Of the studies that did not attempt to correct for confounding variables, all but three suggested that patients undergoing thymectomy are more likely to achieve a drug-free complete remission (an approximately doubled chance) or to improve. Of the four studies that used a case-matched design to try to eliminate multiple confounding variables, three-quarters showed a benefit to thymectomy, but each of these either failed to match for all of the known important variables or was otherwise severely flawed. Finally, of the three studies that utilized multivariate analysis to account for all possible confounding variables, two-thirds showed no significant benefit to thymectomy.
Many neurologists, on the basis of these admittedly inconclusive data, do consider thymectomy to be standard-of-care therapy in selected MG patients, while others recommend it only very rarely or not at all.
The literature in support of thymectomy generally recommends it in patients with Osserman class I (ocular only) or II (mild generalized weakness) MG whose myasthenic symptoms interfere with their lives enough for them to consider undergoing major thoracic surgery.18,35,39,41 The recommendation tends to be stronger for Osserman class 3 MG, where there is a general consensus that patients between puberty and age 60 should undergo thymectomy.29,43 For Osserman class 4 MG and myasthenic crisis, thymectomy is discouraged without an attempt by all available nonsurgical means to bring the disease under control preoperatively.
The role of thymectomy for patients with purely ocular symptoms is perhaps the most controversial issue.19,39 However, if a patient with substantial ocular symptoms prefers surgery to immunosuppressive or cholinesterase-inhibiting drug therapy or if medical treatment has been ineffective, thymectomy is reasonably offered. This becomes a more reasonable approach when an outpatient procedure with minimal morbidity, such as extended TCT, can be offered.
Several studies have demonstrated that young patients have better response rates to thymectomy than the elderly.1,7,18,32,46 The benefits of thymectomy decrease with age, and at some point the risks outweigh the benefits; although with TCT, the age at which this is the case is likely greater. Patients with a short duration of illness prior to surgery have also been reported to be more likely to benefit from surgical intervention.15,36 Thus, there is a premium on performing thymectomy as early after disease onset and at as early an age as feasible, although notably the operation remains particularly controversial in children.14,27,28,44,47,50
The role of gender in determining clinical outcome after thymectomy for MG is also unclear. In some studies, male patients have been noted to be more likely than female patients to achieve disease remission.8 However, in the absence of definitive evidence, it is recommended that thymectomy be offered to both genders without prejudice.
Specifically with regard to TCT, there are certain preoperative criteria that must be met. Most importantly, the patient must be able to hyperextend his or her neck to a reasonable extent, as access to the mediastinum from the head of the operating table is impossible in a patient who cannot extend. This issue makes the operation difficult in some but not all elderly patients. Morbid obesity is also a relative contraindication, as neck extension and also the lifting of the sternum essential to the operation may be compromised in such patients. Prior mediastinal surgery is a strong contraindication, and most feel that TCT is also contraindicated in the presence of known or suspected thymoma. It should be noted, however, that as experience with the operation grows, complete resection of small, clearly noninvasive thymomas can be reliably performed.
In class I to III myasthenic patients who meet these criteria, we recommend TCT. Transcervical thymectomy offers these patients fewer complications, less postoperative pain, a far shorter length of stay, and very similar remission rates as compared with procedures performed via median sternotomy.
Preoperative Preparation
Patients with myasthenia gravis can undergo a thymectomy with limited morbidity provided that a careful preoperative preparation is carried out. The minimally invasive nature of TCT without doubt reduces morbidity versus MS approaches, but it does not reduce the importance of preoperative optimization of disease status. In more advanced patients, this requires the combined
efforts of teams from neurology, anesthesiology, and thoracic surgery who have experience in the care of these patients.
efforts of teams from neurology, anesthesiology, and thoracic surgery who have experience in the care of these patients.
During preoperative evaluation, patients found to have more than mild generalized symptoms, bulbar symptoms, or respiratory symptoms despite drug therapy are generally referred for plasmapheresis,34 since these patients are at high risk for aspiration, pneumonia and reintubation postoperatively.19,48 This not only facilitates the postoperative recovery but also allows tapering of corticosteroids to low levels prior to surgery. Patients with substantial pulmonary symptoms also undergo preop pulmonary function testing. Forced vital capacity (FVC) has also been found to be a useful tool to monitor postoperative progress.48
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
