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54 Thymectomy

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the reasons that many neurologists refer only the occasional patient for thymectomy despite the recognition that many patients have a beneﬁcial response. Much of this reluctance is predicated on the “size” and perceived magnitude of the operation, namely a median sternotomy, which is the procedure most commonly employed for thymectomy. Less invasive approaches to thymectomy, speciﬁcally the transcervical approach as presented in this chapter, should go a long way toward addressing many of these concerns.

Speciﬁc preoperative testing prior to thymectomy is limited to CT scanning of the chest and measurement of pulmonary function. The CT scan of the chest is used to assess for the presence of a thymoma, a ﬁnding that could dictate the operative approach. The key ﬁnding, in addition to whether or not a thymoma is present, is an assessment of size and whether the mass appears to be encapsulated or invasive. The deﬁnitive assessment of invasion can only be made at the time of operation, but often a fairly reliable assumption regarding encapsulation can be made. A CT scan of the chest should be obtained in all patients following a diagnosis of MG to speciﬁcally exclude a thymoma, a ﬁnding present in up to 30–40 per cent of these patients. A measurement of forced vital capacity (as a minimum) should be made to ascertain whether any involvement of respiratory muscles exists, a ﬁnding that could have implications following general anesthesia and the operation. Respiratory muscle involvement, if severe, could be predictive of a postoperative mechanical ventilation requirement and would clearly mandate the need for more intensive preoperative preparation.

Prior to thymectomy, patients should be managed with optimal medical therapy following establishment of the speciﬁc diagnosis of MG. First-line therapy in MG usually consists of pyridostigmine, an anticholinesterase inhibitor, given as a single agent. The majority of patients experience signiﬁcant relief of symptoms following initiation of this drug, and in most patients it is the only drug needed. Corticosteroids, speciﬁcally prednisone, is the most commonly used immunosuppressive agent for treating the symptoms of MG and may be necessary in the occasional patient who responds less than optimally to pyridostigmine. Other immunosuppressants, speciﬁcally azathioprine, may also be used. Prior to operation, depending on the judgment of the referring neurologist, plasmapheresis may be performed that usually consists of three plasma exchanges carried out during the week preceding the operation. This procedure signiﬁcantly reduces the

level of circulating antiacetylcholine receptor antibodies. Depending on venous access, this procedure may be done on an outpatient basis. Following plasmapheresis, patients usually report feeling better than they have done in many months. Plasmapheresis should be performed for patients with reduced vital capacity, though this procedure becomes less important when the thymectomy is performed via the transcervical approach.

ANESTHESIA

General anesthesia can be performed safely in patients with MG following optimal preparation and adequate monitoring of neuromuscular transmission during and following the surgical procedure. Patients are requested to take their medication on the morning of the operative procedure just as they would normally. Because of the decreased number of acetylcholine receptors or their functional blockade by antibodies directed against them, the use of succinylcholine or other nondepolarizing muscle relaxants is avoided. Other types of muscle relaxants can be used in smaller amounts as part of a balanced technique of anesthesia. It is important that an anesthesiologist experienced in the care of patients with MG be part of the team in order to avoid postoperative problems. Neuromuscular transmission should be monitored during the operation by peripheral nerve stimulation to aid in titrating the dose of muscle relaxants and to ensure complete reversal of neuromuscular block at the conclusion of the procedure. A detailed discussion of anesthetic technique is beyond the scope of this chapter but may be found in the paper by Bazaka.

OPERATION

The standard operation for thymectomy in patients with MG consists of a median sternotomy with total removal of all thymic tissue. This operation is essentially the same operation as described for excision of an anterior mediastinal mass in Chapter 3, so that a detailed description will not be provided in this chapter. The critical factor for thymectomy in the patient with MG is complete removal of the thymus gland. Some have argued that aberrant rests of thymic tissue are so common that more radical operations are justiﬁed.

Masaoka ﬁrst described the extended trans-sternal

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thymectomy where not only the gross thymus but also the surrounding adipose tissue in the anterior mediastinum is removed.

Operation 55

Skin incision

Thymus gland

This procedure removes all thymic tissue as well as adipose tissue from the lower poles of the thyroid (superior extent) to the diaphragm (inferior) and from phrenic nerve to phrenic nerve (posterior). A modiﬁcation of this procedure, the maximal thymectomy, was advocated by Jaretzki and others and involves a cervicomediastinal approach with both a cervical incision and median sternotomy. The extent of this procedure exceeds that of the extended thymectomy by including the cervical region, the aortopulmonary window, and the lateral region of the phrenic nerves. The pericardium is taken along with both pleural reﬂections. As might be expected, the incidence of complications following this procedure exceeds that reported for other procedures including phrenic and recurrent laryngeal nerve injuries as well as postoperative respiratory failure.

Despite the assumption made by advocates for the more

extensive procedures, it seems likely that in a patient with multiple aberrant rests of thymus any procedure will remove all thymic tissue, especially since many of these areas are visible only microscopically. Indeed, results with a less invasive approach, transcervical thymectomy, are equivalent to those achieved by the “extended” approaches with signiﬁcantly less morbidity and shorter hospital stay.

Our preferred operation for thymectomy is via the transcervical approach utilizing the technique popularized by Joel Cooper. This less invasive approach is contraindicated only when a large thymoma (>4 cm) is present or hyperextension of the neck is unable to be achieved. Otherwise, cervical thymectomy is the approach that we have now used in over 200 patients.

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Retrothyroid (6%)

Attached by cord (20%)

Accessory cervical lobe (98%)

The patient is positioned supine with an inﬂatable bag

behind the scapulae and with the neck hyperextended. A transverse skin incision is made just at the level of the sternal notch and deepened through the platysma. Superior and inferior subplatysmal ﬂaps are raised so as to maximize the operative ﬁeld and allow for the placement of skin retractors. Dissection is carried along the midline separating the right and left strap muscles, speciﬁcally the sternohyoid and sternothyroid muscles. The sternothyroid muscle is elevated, and the dissection proceeds along the posterior surface of the muscle.

Thymus in cervical fat (22%)

A-P window (24%)

Behind innominate vein (3%)

Cervical mediastinal lobes (98%)

Lateral to phrenic nerves (72%)

Extracapsular mediastinal lobes (90%)

Thymus in mediastinal fat (32%)

Left lobe of thymus gland

Trachea

Sternothyroid muscle

Right lobe of thymus gland

Sternohyoid muscle

The lobe of the thymus gland is identiﬁed anterior to the

inferior thyroid vein. The gland can be distinguished from adjacent fat by its salmon pink color and by the presence of a capsule. Once the gland is identiﬁed it is freed up laterally and medially, and the dissection proceeds superiorly while applying downward retraction on the gland. This maneuver allows for complete dissection of the gland up to its origin where a small vein usually is found. The vein is clipped, and the gland is mobilized anteriorly and freed away from adjacent structures. A silk ligature is placed at the apex of the lobe of the gland to be used as a “handle” to facilitate the mobilization. Dissection then proceeds toward the mediastinum until the innominate vein is encountered. Both lobes of the gland are freed away from surrounding structures in a similar manner. Locating one lobe of the gland leads to the other lobe as the dissection proceeds in a caudad direction. The gland is always located anterior to the inferior thyroid veins, and the veins are dissected away from the gland and left intact.

Operation 57

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Both lobes of the gland are lifted anteriorly, and using

blunt dissection with peanut sponges, the gland is separated away from the innominate vein. As this maneuver proceeds, individual thymic venous branches come into view. These branches are individually ligated and divided. The number of branches varies, but usually at least two or three are identiﬁed and must be divided in order to mobilize the gland away from the vein. Care must be taken to avoid avulsing one of these venous branches since bleeding is difﬁcult to control in the limited operative ﬁeld. The gland usually courses anterior to the innominate vein, but in the occasional patient either a lobe or the entire gland may pass posterior to the vein. This anatomical variant needs to be recognized and dealt with appropriately so as not to leave any residual gland. Using ball sponges on a ring forceps, the gland is separated away from the sternum anteriorly.

Left lobe of thymus gland

Tributaries to innominate vein (thymic venous branches)

Right lobe of thymus gland

Innominate vein

Cooper thymectomy retractor

Thymus gland

The Cooper Thymectomy Retractor (Pilling-Weck Co.,

Ft. Washington, PA) is put in place to further deﬁne the operative ﬁeld and allow for better visualization of the anterior mediastinum. This retractor attaches to the operating table, and the L-shaped blade is placed behind the sternal notch and lifted. The inﬂatable bag is deﬂated so that an optimal view of the mediastinum is provided. If the neck is able to be well extended, the entire thymus gland may be visualized, and the mediastinum is viewed down to the diaphragm with appropriate downward traction applied to the pericardium.

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Once the retractor is in place, additional skin retraction

is provided by an army-navy retractor placed on each side of the incision held in place by Penrose drains attached to the arms of the Cooper retractor. The gland is completely dissected away from the pericardium down to its inferior extent by blunt dissection with ball sponges. Likewise, the gland is completely separated from the sternum anteriorly. The gland is bluntly dissected away from the right pleural reﬂection and reﬂected from right to left. Care is taken to avoid entry into the pleural space; but if a rent is made in the pleura, the lung simply is re-expanded at the time of closure by placing a red rubber tube through the pleural rent while the anesthesiologist inﬂates the lungs. The gland is easily distinguished from pleural fat by the difference in appearance and texture. The gland readily separates from the pleural reﬂection with blunt dissection. Once the gland is freed off the right pleural reﬂection, the left lobe is likewise freed. Often, a tongue of gland tracks down into the aortopulmonary window, and this extension needs to be followed to its termination to assure complete removal of the gland. All of the dissection in this area is done bluntly, taking care to avoid any signiﬁcant traction on the phrenic nerve. The gland is then reﬂected from inferiorly up into the neck sweeping off any residual pericardial attachments, some of which may need to be divided sharply. Following this maneuver the gland is delivered into the neck and removed. With the retractor still in place a thorough inspection is made to assure hemostasis as no drains are left. Both pleural reﬂections should be assessed for integrity. The retractor is then removed. The neck is closed in layers in the usual fashion, ﬁrst reapproximating the strap muscles in the midline followed by a subcuticular skin closure.

Pericardium Right pleural reflection

Cervical portion of thymus gland

Innominate vein

Mediastinal thymus gland

Thymus gland

Pericardium

Sternum

Lung

POSTOPERATIVE CARE

With careful neuromuscular monitoring the patient should be easily awakened and extubated prior to transfer to the postanesthesia recovery area. A chest radiograph should be obtained to assure that both lungs are fully inﬂated in case any entry into the pleural space had been made. Preoperative medications are resumed as soon as the patient is fully awake and able to take ﬂuids by mouth. Patients are watched for several hours in the recovery area prior to discharge. Routinely in our experience, patients are discharged home on the day of the procedure, though early in our experience they were discharged on the morning of the ﬁrst postoperative day. Mild analgesics are prescribed for the postoperative discomfort, and patients usually return to full activity within 1 week.

OUTCOME

The goal of thymectomy in MG is the induction of remission or improvement of symptoms with less reliance on medication. Remission can be expected in 40–50% of patients undergoing thymectomy, but the time that it takes to achieve

this rate may be somewhat prolonged. Patients may see continued improvement for up to 18 months following operation, and some patients may not go into remission until some time after that. Our data and that from Cooper’s group suggest that results obtained following transcervical thymectomy do not differ from those obtained via the trans-sternal route, either the extended or the maximal approach.

FURTHER READING

Baraka A. Anesthesia and critical care of thymectomy for myasthenia

gravis. Chest Surgery Clinics of North America 2001; 11: 337–61.

Blalock A, McGehee HA, Ford FR, et al. The treatment of myasthenia

gravis by removal of the thymus gland. Journal of the American Medical Association 1941; 117: 1529.

Bril V, Kojic J, Ilse WK, et al. Long-term clinical outcome after

transcervical thymectomy for myasthenia gravis. Annals of Thoracic Surgery 1998; 65: 1520–2.

Jaretzki A III, Wolff M. Maximal thymectomy for myasthenia gravis:

surgical anatomy and operative technique. Journal of Thoracic and Cardiovascular Surgery 1988; 96: 711–6.

Masaoka A, Yamakawa Y, Niwa H, et al. Extended thymectomy for

myasthenia gravis patients: a 20-year review. Annals of Thoracic Surgery 1996; 62: 853–9.

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Chylothorax

ROBERT J. CERFOLIO MD, FACS, FACCP

Associate Professor of Surgery, Chief of Section of Thoracic Surgery, University of Alabama at Birmingham; Department of Surgery, Division of Cardiothoracic Surgery, Birmingham, Alabama, USA

HISTORY

Munk and Rosenstein ﬁrst described chylothorax in 1891. They noted that the clear pleural efﬂuent from a patient’s chest tube turned milky when the patient ate a fatty meal. Chylothorax is now deﬁned as the presence of lymphatic ﬂuid in the pleural space that results from a leak in the main thoracic duct or one of its branches. Chylothorax is suggested today, as Munk described over 100 years ago, by the presence of milky drainage from a tube that is in the chest, or the accumulation of this type of ﬂuid in the pleural space. The diagnosis is conﬁrmed by analysis of the efﬂuent with measurement of a triglyceride concentration that is greater than 110 mg/dl. The diagnosis may also be established by the presence of fat and chylomicrons via microscopic examination of the efﬂuent. Staining with Sudan-3 is another diagnostic test because it highlights fat globules. If the patient is not eating, the ﬂuid may not be milky, and the diagnosis should be suspected by a persistently high, unexplained chest tube output in a patient with stable hemoglobin who does not have a subarachnoid–pleural ﬁstula.

Thoracic duct ﬂuid is a mixture of chyle, which contains cholesterol, protein, and lymphatic ﬂuid, from the small intestine. The main cellular element is lymphocytes. In the past chylothorax had extremely high operative mortality because it used to lead to leukopenia and malnutrition mainly because of delayed treatment. However, because of a heightened awareness of this problem by surgeons, chylothorax is being more quickly diagnosed and treated.

Chylothorax is classiﬁed as congenital, traumatic, neoplastic, spontaneous, or miscellaneous. Operative chylothorax (an iatrogenic subset of the traumatic type) is the most common form that the surgeon needs to address operatively, and this type will be the main scope of this chapter. A 1996 report found chylothorax to be a very rare complication

after a general thoracic surgical procedure. We found the incidence of chylothorax to be 0.26% after lobectomy and

0.37% after pneumonectomy. However, after esophagectomy, we found this complication to occur in 2.9% of patients. Because esophagectomy is by far the most common setting in which chylothorax requires operative intervention, we will focus on this operation in the remainder of this chapter.

PRINCIPLES AND JUSTIFICATION

The best way to manage chylothorax after esophagectomy is to prevent it. Prevention is best accomplished during an Ivor Lewis-type approach by carefully examining the posterior mediastinum prior to doing the esophageal–gastric anastomosis. The thoracic duct, if visualized, should be ligated. If it is not seen, sponges should be placed in the area and should be observed for 1 minute to ensure that clear ﬂuid does not collect. Similarly, during a transhiatal approach, the posterior mediastinum at the hiatus should be examined prior to passing the conduit from the abdomen to the neck.

PREOPERATIVE ASSESSMENT AND PREPARATION

Once diagnosed postoperatively, chylothorax usually requires operative intervention. We have shown that if the chest output is consistently greater than 1000 ml per day for 4–5 days after esophageal resection, nonoperative management with total parenteral nutrition or medium chain triglycerides diet will probably fail. Because esophagectomy, coupled with a high output, suggests an injury to the main duct or to a major tributary, thoracic duct ligation is required. Delay can lead to

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serious morbidity. Lymphangiography prior to surgery can be helpful. This test may demonstrate a leak from a large collateral, and this information can help guide treatment. Moreover, 40% of patients have a thoracic duct that has an atypical course. Lymphangiography helps not only to identify the leak, but also to identify the course of the main thoracic duct that may help in ligation. A gastrograﬁn swallow should be performed prior to reoperation to ensure no anastomotic leaks exist. If one is present, perhaps that can be addressed at the same time as the chylothorax. Usually, though, a small anastomotic leak is best left alone as it will heal on its own.

OPERATION

Once surgical intervention is decided, many surgical approaches are available. The options include both a right and left video-assisted thoracoscopy, laparoscopy, redo celiotomy, right or left thoracotomy, and even a neck approach. The site of drainage is the most important deter-

minant as to the side and type of surgical approach chosen. However, if a patient has had an Ivor Lewis operation initially, we prefer a redo right thoracotomy, even if the drainage is mostly coming out of a left chest tube. The duct can be ligated from the right, and this approach saves the patient the morbidity of a left thoracotomy several days after having had a right.

The goal of operative therapy is to ligate the thoracic duct and to also perform a pleurodesis. We prefer a mechanical pleurodesis, but some use chemical pleurodesis. Others have used ﬁbrin glue over the duct as well. Another option is to use a pleural shunt, which we believe does not address the problem, but merely reroutes it.

The best way to identify the chylous ﬁstula at the time of surgery is to give the patient a fatty meal, either through the feeding tube (that many surgeons place at the time of esophageal resection), or though the nasogastric tube. Cream, milk, or olive oil can be given approximately 1 hour before the operation. This maneuver is done so the surgeon can see the duct actively spurting the milky discharge. Once identiﬁed, the duct can be clipped or ligated.

Probably the best and most commonly selected way to

identify the duct is through a right thoracotomy. One may re-enter the chest over the same rib used initially (usually the ﬁfth rib), or go over the eighth rib for easier access to the lower chest.

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Since this reoperation is most commonly performed

after an Ivor Lewis esophagogastrectomy, the gastric conduit lies on top of the main thoracic duct, and this is where most ﬁstulas lie. One needs to mobilize the conduit carefully to avoid injuring the freshly formed anastomosis, which is usually only a few days old, and to avoid injuring the gastroepiploic artery. For this reason, we prefer placing a lap pad along the lesser curve (which always lies against the right chest), and retracting gently with a retractor to lift the conduit up slightly.

Once the duct is visualized with the milky discharge coming out of it, the surrounding tissue should be oversewn with Prolene suture buttressed by pledgets.

If the duct cannot be found, then mass ligation of all of the supradiaphragmatic tissue lying on top of the vertebral body should be performed. This maneuver is done just above the diaphragm on top of the vertebral body. Fibrin glue can then be placed over this area as well. Others have described the use of talc. Mechanical pleurodesis helps create pleural symphysis and helps prevent the re-accumulation of chyle. The system should be continuously challenged with a fatty meal prior to closure, to ensure that the ﬁstula has been properly closed. The chest is closed with a right angle chest tube placed posterior-inferior and a straight chest tube placed apicalanterior.

POSTOPERATIVE CARE

Keys to good postoperative care include challenging the patient with a high fatty meal both via tube feeds initially and later by mouth, prior to removing any chest tubes. If mechanical and/or chemical pleurodesis has been performed, and if no air leaks exist, we prefer leaving the chest tubes on suction. The patient should have chest physical therapy, nebulizer treatments, frequent ambulation daily, incentive spirometry, and strict aspiration precautions.

OUTCOME

With quick diagnosis, careful intraoperative management and diligent custodial, postoperative care results are out-

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standing. Early intervention is crucial; and when performed, most patients have few to no sequelae. This complication may only add a few extra days to the usual 7-day postoperative course that most patients who undergo Ivor Lewis esophagogastrectomy currently have.