Adult Chest Surgery

Chapter 136. Radical Transsternal Thymectomy 

The thymus gland is one of the more common structures in the anterior mediastinum that requires surgical extirpation. The common indications for thymectomy are thymic neoplasm and treatment of the autoimmune disorder myasthenia gravis (MG). Thymus removal should be a safe, straightforward procedure. The key elements in successful and complete thymectomy depend on a comprehensive knowledge of the anatomic and embryologic characteristics of thymic development and the physiology of thymic disease.

EMBRYOLOGY AND ANATOMY

The word thymus comes from a Latin derivation of the Greek thymos because of its resemblance to the flowers of the thyme plant. The thymus is a lymphoepithelial organ that is derived embryologically from the third pair of pharyngeal pouches that descend caudally and medially beginning in the seventh week of life (Fig. 136-1). Through a complex series of migrations, these anlagen continue to descend in a caudal and medial direction. The hollow primordia rapidly become solid epithelial bars, and during the eighth week, the caudad ends of the paired components of the thymus fuse together to form what is generally a four-lobed gland that attaches to the anterior pericardium. This attachment enhances the descent of the thymus into the thorax while the cephalic extremes of the organ become attenuated and generally disappear. However, migration can be incomplete, and remnants (or rests) may be deposited at any point along the excursion of the primordia. In addition to being embedded within the thyroid gland or associated with the parathyroid glands, aberrant thymic rests occur independently along the entire path of thymic descent in as many as 20% of humans.The lower lobe capsule tends to be less distinct, and thymic corpuscles, as well as abundant lymphocytes, trail off into the surrounding mediastinal fat and nodal tissue. The thymus gland itself can occupy a cervical position, reaching occasionally as far cephalad as the hyoid bone. The caudad extremes of the gland can extend as far downward as the xiphoid process.

Figure 136-1.

 

The thymus and parathyroid glands descend from the third and fourth pharyngeal pouches during embryologic development.

 

The thyroid, parathyroid, and thymus share a common origin from the primordial pharynx and its pouches. The inferior parathyroid glands are derived from the dorsal wings of the third pair of pharyngeal pouches. As the thymus migrates downward to its definitive position in the anterior mediastinum, the inferior parathyroid glands are pulled down and left behind at the level of the lower poles of the thyroid. The superior parathyroid glands and the ultimobranchial bodies, the source of parafollicular (calcitonin) cells, develop from the fourth pair of pharyngeal pouches, which also can contribute to the development of the thymus. The parathyroid glands are also "parathymic" glands. In autopsy studies, as many as 20% of inferior parathyroid glands invade the thymic capsule in the neck or mediastinum. Although intrathymic parathyroid is well established, there also have been isolated reports of intrathymic thyroid. Ectopic thyroid usually is found along the normal route of its descent from the base of the tongue to the thyroglossal duct. However, rests of thyroid tissue can be found throughout the mediastinum, including the thymus, and can be mistaken as thymic tumors.

At birth, the thymus weighs 10–35 g, and it continues to grow in size until puberty, when it achieves a maximum weight of 20–50 g. It then undergoes progressive atrophy to little more than 5–15 g in the elderly, with the thymic parenchyma being replaced by fibrofatty tissue. The fully developed gland is bilobed, but its exact shape is largely molded by the adjacent structures. It occupies the anterior mediastinum, with the superior horns often extending into the neck, lying deep to the sternothyroid. At completion of its development, the thymus is separated from the sternum by a thin film of loose connective tissue lying anterior to the pericardium and great vessels. It is in especially close contact with the left brachiocephalic (innominate) vein (Fig. 136-2). The gland can extend laterally to the phrenic nerves and is partially covered on either side by the pleural reflections. The arterial supply to the thymus is derived from three sources: the internal thoracic (mammary), inferior thyroid, and pericardiophrenic arteries. However, the principal blood supply is from the internal thoracic arteries. The veins from both lobes ascend between the lobes posteriorly and usually drain into the left brachiocephalic vein or, rarely, directly in the superior vena cava. The numerous veins that leave the lobes generally converge, forming one or two major trunks, although the number of trunks is quite variable (usually between one and five trunks). The inferior thyroid and thyroid internal mammary veins can receive minor tributaries from the cervical portion of the gland.

Figure 136-2.

 

A. Lateral view of the thymus gland shows the relationship of the gland to the left brachiocephalic vein, the inferior aspect of the thyroid gland, and the phrenic and recurrent laryngeal nerves. B. Anterior view of the relationship between the gland and the pericardium and great vessels.

PHYSIOLOGY AND PATHOPHYSIOLOGY

The thymus gland is a central lymphoid organ that performs the important immunologic function of transforming null lymphocytes into thymic or T-lymphocytes, which are responsible for cellular immunity. The maturation of T-lymphocytes appears to be promoted by one or more thymic-derived factors, such as the peptide thymosin. The thymus gland is involved in a variety of immunologic, hematologic, endocrine, infectious, and neoplastic diseases. The thymus can display morphologic changes that can be categorized as anomalies associated with abnormal development, immune deficiencies, hyperplasia, and neoplasia. Symptoms related to thymic disease are categorized as the ones arising directly from the thymic lesion by either compression or invasion, symptoms associated with a previously described clinical syndrome (e.g., MG, red blood cell aplasia, or hypogammaglobulinemia), or nonspecific systemic symptoms such as anorexia and fatigue. Developmental anomalies can involve the location of the thymus or its development. Failure of the thymus to descend into the anterior mediastinum might account for cervical thymic tissue, which can be mistaken for neoplasm, lymphadenopathy, or an enlarged parathyroid. This aberrant tissue can cause compressive symptoms such as respiratory stridor or dysphagia. In general, symptoms are more common and specific in patients with malignancy, whereas patients with thymic cysts and germ cell tumors have symptoms less frequently.

GENERAL PRINCIPLES AND PATIENT SELECTION

Thymectomy has been used with increasing success in achieving palliation and remission in patients with a wide spectrum of disease symptoms.1–4 Most commonly, the indications for extirpation are either thymic neoplasm or the autoimmune disorder MG. Patients with a thymoma should undergo operative resection owing to the potential for invasive spread or morbidity from local mass effects. Biopsy procedures are not advised because of the possibility of tumor seeding.Although 30–60% of thymomas are associated with MG, the relationship is not well understood. Thymomas are found in only 10% of MG patients.

The thymus contains many germinal centers with T- and B-cell areas similar to those seen in lymph nodes. It is known that acetylcholine receptor epitopes are expressed in the thymus of both MG patients and healthy controls on muscle-like myoid cells that are imbedded in the thymic medullary epithelium.These cells are thought to be the source of autoantigen acetylcholine receptor. B cells obtained from the thymus spontaneously synthesize anti-acetylcholine receptor antibody, and thymic T cells are normally clonally restricted. Any alterations in this balance via a virus or a genetic mutation may lead to a loss of tolerance and pathogenicity.7

Most thymic abnormalities are treated by surgical extirpation. However, the surgical approach to thymectomy has been a matter of considerable controversy. Thymectomy must be complete in order to achieve lasting remission or improvement of malignant thymomas or autoimmune disorders such as MG. Today there is consensus that most patients with generalized MG, as well as those with debilitating ocular symptoms not controlled by anticholinesterases, should undergo thymectomy.1–4 There is also general agreement that the goal of thymectomy should be the removal of all thymic tissue in an effort to induce an antigen-specific immunosuppression resulting in functional improvement over time. Not all thymic resections are equal in extent, however, and thus the type of resection performed remains a source of debate.

Based on the anatomic and embryologic origins of the thymus, the key to successful and complete thymectomy is wide exposure and meticulous dissection. Since aberrant thymic rests can exist anywhere along the entire path of thymic descent, as well as within the thyroid or associated with the parathyroid glands, Jaretzki and colleagues have argued that a combined cervical and transsternal approach is necessary to accomplish complete thymic extirpation.Although this "maximal" approach has become the standard by which other resectional procedures are measured, in practice, it does not appear that the morbidity of this exposure, coupled with the increased risk of injury to the recurrent laryngeal, phrenic, and left vagus nerves, justifies the small potential gain over the radical transsternal technique.In the early experience with the transsternal approach, there was a relatively high mortality caused primarily by inadequate respiratory and perioperative support. Thus transcervical thymectomy was long advocated despite the abundant documentation of residual thymic tissue following this approach. More recently, with improved perioperative support and increased experience with median sternotomy, this procedure has become a relatively innocuous approach to the anterior mediastinum and affords far greater opportunity for adequate exposure of the mediastinal structures, permitting complete removal of the gland. Proponents of the transcervical route argue that improved techniques in exposure and visualization of the anterior mediastinum via a cervical incision permit complete excision under direct vision with equivalent results. The advantages of this less invasive approach in terms of morbidity, length of hospital stay, and acceptance of the procedure early in the disease are obvious.However, this method is clearly more difficult to learn and requires considerably more experience than the sternotomy approach. The recent advances in videoscopic technology have led to the use of thoracoscopic visualization of the anterior mediastinum alone or in conjunction with a transcervical incision.This method potentially will provide a minimally invasive technique that may not compromise the exposure and extent of the dissection.

PREOPERATIVE ASSESSMENT

Regardless of the method of thymectomy chosen, preoperative evaluation of the thymus and accurate localization of the mediastinal lesion(s) are very important. When a mass is discovered in the anterior mediastinum (usually on routine chest roentgenogram) or in a patient with MG, the initial workup should include a careful history and physical examination; the neck and particularly the thyroid gland require careful palpation. A complete blood count, serum electrolytes, thyroid function tests, acetylcholine-receptor antibody assay, pulmonary function tests, electromyographic studies, immunoglobulin assay, bone marrow biopsy, and cervical lymph node biopsy may be indicated. Routine chest roentgenography can demonstrate a mass or reveal obliteration or displacement of mediastinal structures. Ultrasound can be used to differentiate between solid and cystic masses. CT scan of the chest is far superior to the other methods in evaluating suspected mediastinal tumors. CT scanning can define the anatomic location, nature, and extent of mediastinal tumors, identify pulmonary metastases, and evaluate the status of mediastinal lymph nodes. However, CT scanning cannot always determine invasiveness. MRI can provide additional views of the thymus as well as more detail concerning invasion and its relationship to adjacent structures.

Removal of the thymus is never an emergency, and preoperative preparation of the patient should be complete before the operation. This step is especially important when performing thymectomy for MG. In these patients, there is usually a lag time of up to 24 months after the thymus is removed and before the results become apparent. The patient's strength and respiratory status should be optimized with the use of pyridostigmine and immunosuppressive agents when indicated. Twenty-two percent of patients with preoperative respiratory insufficiency will require long-term mechanical intubation.10 Preoperative plasmapharesis or IV immunoglobulin therapy may be beneficial in patients with a vital capacity of less than 2 L, suggesting severe pulmonary compromise. The major risk is the presence of oropharyngeal and respiratory muscle weakness that may lead to aspiration of oral secretions, inability to cough effectively, and respiratory failure during the postoperative period.

When performing a thymectomy for MG, the perioperative strategy must be a collaborative effort among the respiratory therapists, primary care physician, neurologist, anesthesiologist, intensivist, and surgeon. The problems associated with postoperative care can be correlated directly with the severity of symptoms at the time of operation.10 Unless patients require preoperative parenteral steroids, hemodynamic stabilization, or plasmapheresis, they can be admitted to the hospital on the day of surgery. In general, anticholinesterase agents (e.g., pyridostigmine bromide) should be discontinued 8 hours prior to operation. Discontinuing these medications any earlier, especially in patients with severe MG, can result in a myasthenic crisis, whereas continuing the medications, particularly in patients with mild symptoms, can result in a postoperative cholinergic crisis. In severe cases, an additional intramuscular injection of a small dose of pyridostigmine bromide can be administered just before the operation. Alternatively, a continuous infusion of neostigmine may be used in severe cases (total daily dose = total daily dose of pyridostigmine bromide divided by 60).If the patient is on steroids, perioperative parenteral steroid coverage is provided, beginning with 100 mg hydrocortisone 1 hour before surgery and continuing every 8 hours for the first 24 hours, then every 12 hours, and then resuming the preoperative oral dosage.Perioperative antibiotics (usually a first-generation cephalosporin) are administered until the mediastinal tubes are removed. Aminoglycoside antibiotics are contraindicated because they increase the neuromuscular block.

TECHNIQUE

Anesthesia

In 1991, Kirsh and colleagues showed in a randomized, prospective, double blinded clinical trial that MG patients who receive a perioperative epidural have less postoperative pain and improved pulmonary function.11General anesthesia can be performed safely with selective use of agents that do not potentiate the neuromuscular defect. While rarely considered, ether should not be used because it will increase the neuromuscular block. Chemical paralysis is not required for a sternotomy. Neuromuscular blocking agents, especially competitive (nondepolarizing) agents, should be avoided because of the long-lasting adverse effects on myasthenic patients. Myasthenic patients are very sensitive to the administration of nondepolarizing agents, which could result in prolonged postoperative respiratory failure. If needed for intubation, a small dose of a noncompetitive depolarizing agent (e.g., succinylcholine) may be used.

Surgical Management

The patient is positioned on the operating table in the supine position. A transverse shoulder roll is placed behind the patient, and the neck is extended with the occiput of the head resting on a "donut" pillow. After induction of anesthesia, a urinary catheter and arterial line should be placed. The operation is carried out via a median sternotomy (Fig. 136-3). The incision can be a midline incision from the sternal notch to below the xiphoid process. Since many of these patients are young women, a more cosmetic incision might be preferable. The more cosmetic Y-shaped skin incision follows the upper contours of the breasts and converges on a point in the midline approximately 10 cm below the sternal notch and continues down the midline to the tip of the xiphoid (Fig. 136-3). A cephalad skin/subcutaneous flap is developed carefully so that cosmesis of the upper chest area is maintained. The superior limit of the subcutaneous dissection is the sternal notch. Electrocautery is used to divide the fascia overlying the sternum. The cleidocleido ligament, which is attached to the posterior surface of manubrium at the sternal notch, is divided vertically, and the sternum is separated from the upper mediastinal structures by blunt finger dissection. Inferiorly, the avascular anterior mediastinal space is entered with finger dissection just below the xiphoid and developed as far cephalad as possible. The sternum is divided longitudinally with a sternal saw.

Figure 136-3.

 

Y-shaped skin incision with a cephalad skin/subcutaneous flap to permit access to the entire sternum for midline sternotomy. The Y-shaped incision provides superior cosmesis of the upper chest area, particularly in females.

 

In adults, obese individuals, and patients on long-term steroids, it is often not possible to distinguish the thymus from the mediastinal fat until the specimen is removed and examined microscopically. Gross and microscopic thymus is found outside the confines of the classic cervical mediastinal lobes in the neck in approximately 30% of specimens and in the mediastinum in approximately 98% of studies.1,3 Therefore, wide exposure and meticulous dissection are needed to remove all the potential thymic tissue completely and safely. An en bloc dissection from diaphragm to thyroid gland and from phrenic nerve to phrenic nerve is undertaken by means of a combination of cautery and sharp dissection of the mediastinal pleura and pericardium. All thymus, suspected thymus, and mediastinal fat, including both mediastinal pleural sheets, are removed.

The mediastinal dissection begins at the diaphragm. The mediastinal fat, including the anterior pericardiophrenic fat pad, is elevated bilaterally and continued superiorly with the lower lobes of the thymus. The mediastinal pleura is incised anteriorly, and once the lower lobes are mobilized bilaterally, the phrenic nerves should be clearly identified. The lymph nodes and fat that course along the nerves are separated from the phrenic nerves on either side anteriorly as part of the en bloc specimen. The thymus is elevated off the pericardium using upward traction and electrocautery (Fig. 136-4). The main arterial supply to the thymus is derived from the internal thoracic arteries, which enter the gland laterally at the level where the isthmus joins the two lobes. Once identified, the arteries and accompanying veins should be isolated and divided in continuity between ligatures. These lateral vessels tend to tether the gland in position, and their division permits the en bloc specimen to be rotated upward to expose the undersurface of the gland (Fig. 136-5). This method is the safest approach to the brachiocephalic vein and the venous drainage of the thymus. The brachiocephalic vein should be exposed and the thymic veins isolated and divided in continuity between ligatures. The thymus then can be elevated from the brachiocephalic vein, and the dissection is continued laterally anterior to the phrenic nerves until the entire specimen is tethered only by the cephalic horns of the thymus in the vicinity of the thyroid and inferior parathyroid glands. An attempt should be made to identify and spare the inferior parathyroids and their blood supply, but this step is not always possible. The cephalad extent of the thymus should be isolated carefully, and the branches of the inferior thyroid vessels entering the two horns should be clamped at the superior aspect of the thymic lobes, divided, and ligated.

Figure 136-4.

 

After the mediastinal pleura is opened, the thymus is elevated, along with the adherent mediastinal pleura, from the pericardium and separated from the phrenic nerves bilaterally.

 

Figure 136-5.

 

Branches of the internal thoracic arteries are divided to permit the en bloc specimen to be rotated upward, exposing the undersurface of the gland and the draining veins. The exposed brachiocephalic and thymic veins are isolated and divided between ligatures or clips (inset).

It is important to include in the en bloc dissection all the fatty thymic tissues that lie in the sulcus between the superior vena cava and the aorta, as well as the tissues in the region of the aortopulmonary window deep under the brachiocephalic vein. During this part of the dissection, identification and avoidance of the left phrenic and vagus (recurrent laryngeal) nerves, which are especially at risk here, are essential. Injury to either of these nerves would be catastrophic, particularly in a patient with MG. The wide mediastinal exposure obtained by opening both pleural spaces not only ensures complete thymus removal but also helps to safeguard the phrenic and vagus nerves.

Gross evidence of invasiveness is the most important prognostic sign of malignancy. Malignant thymic tumors are notorious for local extension and lack of distant metastases, as well as having a deceptively benign appearance on microscopic examination. When a thymoma is present, the same extensive removal of thymic tissue is performed en bloc with the thymoma. The initial exploration includes palpation and visualization of each hemidiaphragm for possible tumor implants. If the pericardium, lungs, brachiocephalic vein, and sternal periosteum are adherent to the tumor, they are removed en bloc because tumor invasion can be present. Unless a phrenic nerve is nonfunctional from tumor invasion, it should be preserved, if at all possible. Postoperative radiation therapy can be used as adjuvant therapy to control residual unresected tumor.

After the thymectomy and anterior mediastinal dissections are complete, two angled chest tubes are placed through separate incisions in the superior epigastrium and positioned along the diaphragms in both pleural cavities. The sternum is reapproximated using no. 5 stainless steel wire, and the fascia and skin incisions are closed.

POSTOPERATIVE MANAGEMENT

Patients usually are extubated in the OR within 30 minutes of the conclusion of the operation. If the preoperative pulmonary status off cholinergic medications is satisfactory, regardless of the surgical approach, it should be anticipated that myasthenic patients will be extubated immediately postoperatively.They are usually kept in a monitored setting overnight. If the patient does not have an epidural catheter in place, parenteral analgesia can be administered in small intermittent doses of hydromorphone or morphine or self-administered via a patient-controlled analgesia device. Continuous infusions and large boluses of narcotic should be avoided, and parenteral ketorolac can be used as a synergistic agent for breakthrough pain. On the morning after the operation, oral medication and a clear liquid diet are begun and advanced as tolerated. Continuous monitoring is discontinued unless the patient requires further intensive monitoring or respiratory support. The chest tubes are removed when no air leak or significant output is present and the lungs are fully expanded on chest x-ray. These tubes usually can be removed by the second postoperative day. Antibiotics and the continuous epidural infusion are discontinued, and oral narcotic analgesics are started once the chest tubes are removed. Patients with MG are discharged when their symptoms are adequately controlled with oral medication and they are well able to tolerate a regular diet. Most patients are able to return to normal activity and work within 2–3 weeks after transsternal thymectomy.

Tapering of medications in patients with MG begins at various times after operation depending on the judgment of the neurologist caring for the patient. In most patients, tapering can be started in the early postoperative period. However, some patients require more gradual attempts at weaning. This situation is particularly true for patients on large preoperative doses of steroids and for patients with long-standing symptoms before the operation. Such individuals can require weeks to months after the operation to begin a substantial tapering in dosage. Patients who do not achieve drug-free remission by 2 years after thymectomy are unlikely to do so subsequently.

COMPLICATIONS

Postoperatively, the greatest threat to the patient's life in MG is weakness and fatigability of the respiratory and oral or pharyngeal musculature. Although rare, a ventilator may be required to support intercostal muscle and diaphragm weakness. Measurement of forced vital capacity is the most useful tool to monitor pulmonary function perioperatively. Anticholinesterase medication generally is not given in the immediate postoperative period because many patients have an increased sensitivity to these drugs, poor relief of their weakness, or a decreased need for these medications. Additionally, drug toxicity can be confused with symptoms of myasthenic crisis. A myasthenic patient with respiratory insufficiency or inability to maintain a patent airway is said to be in "crisis," and this is the greatest danger postoperatively.A postoperative myasthenic crisis is rare, but when it occurs, the patient is unable to maintain an open airway free of secretions or an adequate ventilatory exchange because of failing muscle function. If the patient develops respiratory difficulties or signs of an exacerbation of myasthenic symptoms, a trial dose of edrophonium chloride should be given. If this medication results in prompt improvement in the patient's strength, small doses of a long-acting anticholinesterase drug such as pyridostigmine bromide (approximately one-thirtieth of the oral dose) should be administered cautiously by intramuscular or very slow IV injection until a salutary effect is achieved. The patient should be monitored for signs of overmedication. These would include diaphoresis, muscle fasciculation, excessive salivation, myosis, and wheezing.10 Stress doses of steroids should be used concomitantly. If rapid improvement does not ensue, plasmapheresis should be started and continued for 3 days and then every other day until symptoms can be controlled by oral medications.

Fortunately, the incidence of postoperative myasthenic crisis is rare today and likely reflects the rarity of the state overall. The overall incidence of crisis among MG patients remains about 15–20%, but the mortality rate has declined over time.In the 1950s, the mortality rate of a patient with a myasthenic crisis was approximately 80%. It dropped to 6% in the 1970s and 4% in 1994. This overall decrease in mortality can be attributed directly to advances in management of the critically ill patient.6

RESULTS

Previously, the mortality and considerable morbidity associated with transsternal thymectomy in MG were caused primarily by respiratory complications. Improvements in the surgical technique, anesthesia, respiratory care, and the use of IV immunoglobulin or plasmapheresis in severe cases of MG have markedly reduced the mortality and morbidity of the procedure. Thymectomy is now recognized as a standard procedure in combination with medical management for MG. Most surgeons today performing transsternal thymectomy use an extended procedure that includes removal of intracapsular thymic tissue as well as a radical dissection of the anterior mediastinal fat.1,3 Most series report low rates of morbidity, little or no perioperative mortality, and similar rates of patient improvement and remission.4,12 In a large series of 662 patients undergoing radical transsternal thymectomy for MG over 15 years, Maggi and colleagues demonstrated a remission rate of 38% and a symptom improvement rate of 87% in 500 patients without thymoma.13 A similar evaluation of the short- and long-term experience at the University of Cincinnati supports the utility of this technique. We conducted a retrospective review of 64 consecutive patients operated on between 1979 and 2000. Drug-free remission was achieved in 50% of patients with Osserman grade 1 or 2, whereas patients with more advanced stages of the disease responded to surgery with overall improvement in their symptoms and drug requirements. Symptoms were absent or improved in 76.8% of patients. When followed out greater than 10 years, these numbers improved to 71.4% (remission) and 85.7% (improved), respectively. In addition, mean dosages of prednisone and pyridostigmine bromide were decreased by 69.3% and 58.8%, respectively.14 These results confirm the findings of other investigators that early thymectomy, before progression of symptoms, influences the progression of this disease and should be offered routinely to patients.

SUMMARY

There continues to be critical debate regarding which thymectomy technique is the procedure of choice. The debate persists primarily because there is a lack of controlled, prospective outcome data. The standard transsternal thymectomy was used by Blalock and colleagues and other pioneers of thymic surgery.15 Its efficacy was limited by the removal of only the cervical and mediastinal lobes, originally thought to be the entire gland. Findings by Rosenberg and colleagues, Jaretzki and colleagues, and others of residual thymus in the neck and mediastinum at reoperation following standard transsternal resection have suggested that this technique is not optimal.1,16 The overwhelming evidence that thymic tissue normally resides outside the intracapsular thymus supports the use of an extended procedure that includes removal of the intracapsular thymic tissue as well a radical dissection of the anterior mediastinal fat.12 This typically amounts to an en bloc resection from thyroid to diaphragm, phrenic nerve to phrenic nerve. It would be presumed that failure to remove this tissue would negatively affect outcome. However, no level I data exist to support this notion. In Cincinnati, our practice is to perform transsternal thymectomy with extended anterior mediastinal dissection based on an understanding of the embryologic origins of thymic tissue.14 Analysis of our data suggests that this meticulous operative technique yields comparable results to more aggressive resections without the associated morbidity.

CASE HISTORY

A 61-year-old man noted ptosis as well as diplopia, and his primary care physician referred him to an ophthalmologist, who made a preliminary diagnosis of ocular MG. Subsequent neurologic evaluation revealed physical signs of generalized MG and a markedly elevated serum acetylcholine receptor antibody. Recently, he had noted some difficulty with chewing, excessive drooling, and a change in his speech to a more nasal tone. He was currently on pyridostigmine bromide 60 mg four times daily. He noted some improvement of his symptoms on the medication, but he still was not at his baseline. The neurologist recommended a surgical evaluation for thymectomy. During the encounter, he became progressively weaker, had difficulty keeping his head up, and phonation became more nasal. The patient reported that he had otherwise been very healthy without any significant medical problems. A CT scan of the chest revealed no evidence of thymoma. Elective transsternal thymectomy was recommended.

In preparation for surgery, the patient underwent an echocardiogram and pulmonary function testing, which were normal. Electrolytes and a complete blood count were within normal limits. He was started on a beta blocker, atenolol 25 mg/d, beginning 1 week before surgery. Preoperatively, an epidural catheter was placed for perioperative pain management. The patient underwent an uncomplicated transsternal thymectomy that removed a 430-g thymus (Figs. 136-6, 136-7, and 136-8). He was extubated in the OR and admitted to the ICU on 2 L of nasal cannula O2. Forced vital capacity was noted to be 800 mL. On the night of surgery, the patient was given an IV dose of pyridostigmine bromide, which improved his respiratory effort. On the morning of the first postoperative day, he was started on clear liquids and restarted on his oral medications. A repeat forced vital capacity determination was noted to be 1.2 L. Later that day, the patient was transferred to a surgical floor and advanced to a regular diet. On postoperative day 2, the patient sat in a chair without difficulty. His lungs were fully expanded on his postoperative chest x-ray. There was no air leak, and the chest tubes were noted to have output of less than 150 mL per shift and were removed. This was followed by removal of the epidural and urinary catheters and cessation of perioperative antibiotics. The patient was ambulating without difficulty and tolerating a regular diet and was discharged to home on the third postoperative day on oral narcotic analgesics as well as his preoperative pyridostigmine and atenolol. Final histology on the thymectomy specimen revealed thymic hyperplasia with germinal centers.

Figure 136-6.

 

The thymus, including left pleura, is dissected off the brachiocephalic vein.

 

Figure 136-7.

 

Gross specimen from a radical thymectomy.

 

Figure 136-8.

 

The appearance of the operative bed after thymectomy.

Over the course of the next 6 months, the patient noted moderate subjective improvement in his muscle strength. The ptsosis and diplopia resolved. His neurologist successfully tapered the pyridostigmine bromide down to 30 mg qid with plans to continue a gradual taper as long as the patient continued to improve.

EDITOR'S COMMENT

The traditional argument for radical thymectomy is the infrequent, but real, incidence of ectopic (discontinuous) thymic tissue. In addition, visual inspection is frequently inaccurate: The thymus gland may resemble the surrounding fat tissue and microscopic thymic tissue cannot be grossly identified. The counter-argument is that most patients do not need radical thymectomy; certainly, the efficacy of the operation is unclear. Furthermore, some of the potential sites of ectopic thymic tissue (roughly paralleling the potential sites of ectopic parathyroid tissue) are not addressed even with radical thymectomy. Perhaps reflecting an acknowledgement of both arguments, most surgeons are selective in their use of radical thymectomy.

–SJM

REFERENCES

1. Jaretzki A, Steinglass KM, Sonett JR: Thymectomy in the management of myasthenia gravis. Semin Neurol 24:49–62, 2004. [PubMed: 15229792]

2. Kirschner PA: The history of surgery of the thymus gland. Chest Surg Clin North Am 10:153–165, 2000. [PubMed: 10689534]

3. Nussbaum M: Transsternal, transcervical, and thoracoscopic thymectomy for benign and malignant disease. In Baker RJ, Fischer JE (eds): Mastery of Surgery. Philadelphia, Lippincott Williams & Wilkins, 2001:530–42.

4. Wilkins KB, Bulkley GB: Thymectomy in the integrated management of myasthenia gravis. Adv Surg 32:105–33, 1999. [PubMed: 9891741]

5. Persico G, Martignetti A, Imbriani A, et al: Role of surgery in thymic disorders. Ann Med 31:70–2S, 1999. 

6. Keesey JC: Clinical evaluation and management of myasthenia gravis. Muscle Nerve 29:484–505, 2004. [PubMed: 15052614]

7. Scherer K, Bedlack RS, Simel DL: Does this patient have myasthenia gravis? JAMA 293:1906–14, 2005. [PubMed: 15840866]

8. Calhoun RF, Ritter JH, Guthrie TJ, et al: Results of transcervical thymectomy for myasthenia gravis in 100 consecutive patients. Ann Surg 230:555–9; discussion 559–61, 1999. 

9. Sugarbaker DJ: Thoracoscopy in the management of anterior mediastinal masses. Ann Thorac Surg 56:653–6, 1993. [PubMed: 8379763]

10. Kernstine KH: Preoperative preparation of the patient with myasthenia gravis. Thorac Surg Clin 15:287–95, 2005. [PubMed: 15999526]

11. Kirsch JR, Diringer MN, Borel CO, et al: Preoperative lumbar epidural morphine improves postoperative analgesia and ventilatory function after transsternal thymectomy in patients with myasthenia gravis. Crit Care Med 19:1474–9, 1991. [PubMed: 1959365]

12. Zielinski M, Kuzdzal J, Szlubowski A, Soja J: Comparison of late results of basic transsternal and extended transsternal thymectomies in the treatment of myasthenia gravis. Ann Thorac Surg 78:253–8, 2004. [PubMed: 15223438]

13. Maggi G, Casadio C, Cavallo A, et al: Thymectomy in myasthenia gravis: Results of 662 cases operated upon in 15 years. Eur J Cardiothorac Surg 3:504–9; discussion 510–1, 1989. 

14. Stern LE, Nussbaum MS, Quinlan JG, Fischer JE: Long-term evaluation of extended thymectomy with anterior mediastinal dissection for myasthenia gravis. Surgery 130:774–8; discussion 778–80, 2001. 

15. Blalock A, Mason MF, Morgan HJ, Riven SS: Myasthenia gravis and tumors of the thymic region: Report of a case in which the tumor was removed. Ann Surg 110:544–61, 1939. [PubMed: 17857470]

16. Rosenberg M, Jauregui WO, Herrera MR, et al: Recurrence of thymic hyperplasia after trans-sternal thymectomy in myasthenia gravis. Chest 89:888–9, 1986. [PubMed: 3709255]



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