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Transcervical Thymectomy

  • Bryan F. Meyers
    Correspondence
    Address reprint requests to Bryan F. Meyers, MD, 3108 Queeny Tower, One Barnes-Jewish Hospital Plaza, St. Louis, MO 63110
    Affiliations
    From the Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO
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      Removal of the thymus gland is an accepted component of the overall therapy for myasthenia gravis. As yet there is no clearly delineated pathophysiology to explain the role of the thymus in the generation of myasthenia gravis, but over the past several decades it has become increasingly clear that a complete thymectomy improves the clinical course of patients with myasthenia. This article outlines the techniques and results from transcervical thymectomy for myasthenia gravis.
      Patients with thymomas are generally treated with sternotomy, with the transcervical approach reserved for patients with thymic hyperplasia or normal thymus seen on computed tomography (CT) scan. A recent report suggests that the transcervical approach may be appropriate for small tumors as well, but such extended indications should be used only by those familiar with the technique in typical patients.
      • Deeb ME
      • Brinster CJ
      • Kucharzuk J
      • et al.
      Expanded indications for transcervical thymectomy in the management of anterior mediastinal masses.
      Patients with previous median sternotomy for other reasons are controversial candidates, and careful consideration should be given to full or partial sternotomy.

      Surgical Technique

      Figure thumbnail fx1
      1A general anesthetic is provided with a single lumen endotracheal tube that is secured low to avoid obstruction of the surgeon's view. The intravenous line is placed in the right arm to avoid obstruction when the innominate vein is compressed. If an arterial line is necessary, the anesthesiologist is advised to use the left arm because compression of the innominate artery throughout the surgery may lead to false determinations of low blood pressure in the right radial artery. An inflatable pillow behind the shoulders elevates the shoulders and hyperextends the neck. A sternal saw should be ready in case conversion to a sternotomy is required.
      Figure thumbnail fx2
      2The incision is 4 cm in width and reaches a distance of 2 cm above the sternal notch when the neck is hyperextended. The lower flap is elevated in the subplatysmal plane to the sternal notch. The ligamentous insertion of the two sternocleidomastoid muscles (cleidocleido ligament) is divided with electrocautery to allow improved exposure into the substernal plane. The upper subplatysmal flap is elevated to the inferior border of the thyroid. The strap muscles are separated at the midline and the upper poles of the thymus gland are found deep to the sternothyroid muscle and anterior to the inferior thyroid veins. Older patients have often undergone fatty replacement of the thymus and the upper poles will closely resemble the surrounding fat in the neck. By remaining close to the undersurface of the left strap muscles, the left upper pole is reliably found.
      Figure thumbnail fx3
      3This figure shows the surgeon's view in the early dissection. The upper pole veins are doubly ligated and divided, with the silk tie on the thymus left long as a retraction aid. The left superior pole is identified and is dissected down toward the point at which it merges with the right superior pole. The strap muscles are usually retracted laterally by an assistant with a vein retractor; the cutaway view of the straps in this figure is chosen for clarity. The right superior pole is similarly dissected free, and ligatures are placed around both upper poles to allow gentle retraction during the subsequent thymectomy. The upper poles meet around the level of the sternal notch and together pass into the chest, usually anterior to the innominate vein (although in about 5% of cases, one or both of the upper poles may pass posterior to the innominate vein). With the upper poles fully freed to the level of the innominate vein, the prethymic and retrosternal plane is developed with blunt dissection of an examining finger into the substernal location.
      Figure thumbnail fx4
      4Additional development of the substernal plane is performed with a Kitner dissector or a larger sponge stick. The thymus is gently retracted cephalad and forward by the silk ties on the upper poles to display the posterior veins draining directly into the innominate vein. These thymic veins are doubly ligated with silk ligatures and divided. The anterior surface of the innominate vein becomes the posterior border of the thoroughfare into the mediastinum. We have found that electrocautery and surgical clips provide unreliable hemostasis of these thymic veins, because of the multiple instruments and sponge dissectors that pass through this narrow thoroughfare.
      Figure thumbnail fx5
      5The sternum is retracted vipward using a specially designed sternal retractor (Cooper thymectomy retractor, Pilling Co., Fort Washington, PA). The sternum is retracted upward to the point at which the patient is nearly lifted off the inflated shoulder bag. The bag is then deflated, and the thymectomy retractor is indeed suspending the weight of the patient's chest. This allows the head and the shoulders to fall back and provides direct visualization into the mediastinum through the 4-cm incision. Care is taken to ensure that the head is not “floating,” that is, some of the weight of the head must be supported by a foam cushion at the occiput. Small curved retractors (Parker) are placed at the corners of the incision and hooked via looped Penrose drains to the side rails of the operating table to pull the incision edges laterally and toward the surgeon. The combined effects of the upward retraction of the sternum and the downward and lateral pull of the Penrose drains on the Parker retractors produces optimal surgical exposure. The rest of the operation takes place with the surgeon seated and illumination provided by the surgeon's headlight.
      Figure thumbnail fx6
      6After all thymic veins are divided, the dissection is carried along the anterior pericardial surface into the mediastinum. The thymus generally remains encapsulated and is separated without difficulty from the pericardium. If necessary because of adhesions, a portion of pericardium can be removed along with the gland at the site of the adhesion. As the dissection continues deeper into the mediastinum, the bulging pleura on either side commonly obstruct the surgeon's view. With some coordination, the anesthesiologist can intermittently suspend ventilation for a reasonable period to allow better visualization deep into the mediastinum. Using a Kitner dissector or a larger sponge dissector, the surgeon can easily depress the great vessels and allow direct visualization into the aorto-pulmonary window for complete removal of the thymus in this vicinity. Some direct contributing blood vessels can be identified in the form of veins draining into the superior vena cava on the right or small branches of the internal mammary veins from the left or right. These can be dealt with using electrocautery, although care should be taken to avoid injury to the phrenic nerves. Because patients with myasthenia gravis are generally not given a paralytic agent during the course of anesthesia, the proximity of the phrenic nerves will be apparent when electrocautery is used in the mediastinum. Injury to the nerves is exceedingly rare as long as the electrocautery is on a low setting and the point of application is always adjacent to the thymus and not wide in the mediastinum. In most cases, the thymus gland is removed as a complete gland with both upper poles and both lower poles intact. In these circumstances, careful inspection of the remaining tissue in the mediastinum is performed to identify any possible congenital thymus tissue remaining after the removal of the gland. Any suspicious bits of fat in the mediastinum are removed and, if necessary, sent for frozen section to ascertain whether or not they contain thymic tissue. This verification is advised in the surgeon's early experiences, but becomes less important as the techniques become more familiar. A red rubber catheter is placed into the mediastinum, and the deep layers of the incision are closed around it. The catheter is pulled out slowly during a sustained positive-pressure breath, and the skin closure is completed. If either pleural space was entered, the entry should be enlarged to allow evacuation of the pleural space with the red rubber catheter. The skin is closed with a subcuticular suture of absorbable material and Steri-strips. The patient is then extubated and taken to the recovery room for a follow-up upright chest x-ray. The presence of a small pneumothorax does not require remedial action, because the air will be absorbed within a few days.

      Comments

      The short- and long-term outcomes after transcervical thymectomy have been previously reported. Our report of 100 consecutive patients noted a low morbidity rate and no perioperative deaths.
      • Calhoun RF
      • Ritter JH
      • Guthrie TJ
      • et al.
      Results of transcervical thymectomy for myasthenia gravis in 100 consecutive patients.
      The complication rate was 8%, including one seizure, one deep vein thrombosis, one myasthenic crisis, and five episodes of postoperative pneumothorax. No phrenic nerve or recurrent laryngeal nerve injuries occurred. The mean operative time was 104 minutes and postoperative length of stay was just longer than 1 day. In this report, 78 patients had more than 12 months of follow-up and thus were available for long-term analysis. Overall, the median Osserman grade improved from 3 before surgery to 1 after surgery. Eighty-five percent (66 of 78) of the patients improved by 1 or more Osserman grades; 63% (49 of 78) improved by 2 or more Osserman grades. Thirty-five percent achieved complete remission, experiencing no symptoms and requiring no medications. This complete remission rate is as high as 50% if patients who are free of symptoms and off Mestinon therapy but maintained on low-dose steroid therapy at the preference of their neurologist are included. Seventy-one percent (55 of 78) were free of any generalized symptoms of weakness. Only one patient deteriorated by a single Osserman grade, and 14% of the patients (11 of 78) experienced no change in Osserman grade after thymectomy.
      The transcervical approach for thymectomy allows safe, complete removal of the thymus and provides clinical benefit equal to that from more extensive resections.
      • Bril V
      • Kojic J
      • Ilse WK
      • et al.
      Long-term clinical outcome after transcervical thymectomy for myasthenia gravis.
      The low morbidity and short hospitalization after transcervical thymectomy present minimal barriers and should improve the neurologists' willingness to refer suitable patients and increase the patients' acceptance of surgical therapy. In addition, the transcervical approach is attractive for older patients with less likelihood for improvement and for patients at higher risk for complications such as those on high-dose prednisone therapy. Early, safe, and complete thymectomy offers all of the benefits of surgical removal of the thymus to a patient with myasthenia with a minimal risk of morbidity and postoperative pain. The report by Gronseth suggested that multiple confounding variables prevent the comparison of results of uncontrolled trials and, as a result, there is no conclusive evidence of the superiority of one technique over another.
      • Gronseth GS
      • Barohn RJ
      Practice parameter: Thymectomy for autoimmune myasthenia gravis (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology.

      References

        • Deeb ME
        • Brinster CJ
        • Kucharzuk J
        • et al.
        Expanded indications for transcervical thymectomy in the management of anterior mediastinal masses.
        Ann Thorac Surg. 2001; 72: 208-211
        • Calhoun RF
        • Ritter JH
        • Guthrie TJ
        • et al.
        Results of transcervical thymectomy for myasthenia gravis in 100 consecutive patients.
        Ann Surg. 1999; 230: 555-561
        • Bril V
        • Kojic J
        • Ilse WK
        • et al.
        Long-term clinical outcome after transcervical thymectomy for myasthenia gravis.
        Ann Thorac Surg. 1998; 65: 1520-1522
        • Gronseth GS
        • Barohn RJ
        Practice parameter: Thymectomy for autoimmune myasthenia gravis (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology.
        Neurology. 2000; 55: 7-15