Radical Transsternal Thymectomy David Park Mason, MD

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bnormalities of the thymus comprise more than half of generalized enlargement of the thymic gland caused by dif- Athe lesions found in the anterior mediastinal compart- fuse thymocyte proliferation. Thymic hyperplasia is an im- ment in adults. Greater than 95% of the tumors of the thymus munologic condition.10 In children, thymic hyperplasia can are thymomas that originate from thymic epithelial cells. be associated with a variety of endocrine disorders including They generally present as an incidental radiographic finding. hyperthyroidism. In adults, thymic hyperplasia has been as- They are of surgical importance both as isolated entities as sociated with thymoma as well as many immune dysfunction well as in association with myasthenia gravis (MG). Surgical syndromes—the most notable being myasthenia gravis. Re- excision is the cornerstone of therapy for thymoma.1 In ad- moval of the thymus gland, by a variety of surgical ap- dition, thymectomy is an integral component of the manage- proaches, appears to influence the immune dysfunction ob- ment of myasthenia gravis. served in myasthenia gravis.7 The mechanism of this Ludwig Rehn performed the first thymic operation in 1896, a influence, and the relative benefit of removing all residual or transcervical exothymopexy for a patient with an enlarged thy- ectopic thymic tissue, is unclear. 2 mus causing episodes of suffocation. He pulled the enlarged The most frequent asymptomatic indication for thymec- thymus out of the mediastinum and performed a pexy of the tomy is thymoma. Chest CT scan imaging of the thymus thymic capsule to the posterior aspect of the manubrium. Trans- gland is often diagnostic of a thymic mass because the thymus cervical thymic surgery was generally the preferred route until gland is the only anatomic structure anterior to the brachio- the 1930s. In 1936, Dr. Alfred Blalock performed the first suc- cephalic vein. Thymomas are not associated with lymphade- cessful transsternal thymectomy through an upper median ster- nopathy. The presence of a separate aortopulmonary window notomy in a patient with myasthenia gravis and a large anterior mass or paratracheal adenopathy should raise the possibility 3 superior mediastinal tumor. of lymphoma. Similarly, Hodgkin’s disease can be associated Radical transsternal resection evolved from this approach and with thymic enlargement.11 the surgical technique now focuses on the en bloc resection of In most cases, the radiographic appearance of thymoma is the entire thymus and pericardial fat pad from the thyroid gland sufficient to preclude the necessity of a tissue biopsy before down to the diaphragm and laterally to the phrenic nerves. This surgical resection. Further, tissue biopsy is notoriously inef- is performed through a full sternotomy. Advantages of this ap- ficient because of the marked heterogeneity within the thy- proach are direct and safe access to the entire anterior mediasti- mus gland. It is common for a resected thymoma to reflect num. Opening the pleural spaces allows visualization and pres- areas of lymphocyte predominance (stage I) and epithelial ervation of the phrenic nerves. Advocates of this approach feel predominance (stage III) within the same tumor.8,12 Al- that radical resection is the technique that is most likely to re- though the subsequent development of pleural implants is move all thymic tissue and give the highest likelihood of cure, commonly attributable to presurgical biopsy, the supportive particularly in the setting of myasthenia gravis.4,5 They point to the fact that even small portions of remnant thymic tissue has data are weak. Pleural implants clearly occur without prior been associated with recurrent myasthenic symptoms and that biopsy. Similarly, needle or mediastinotomy biopsy is infre- reoperation after transcervical thymectomy has been required quently associated with localized pleural disease. Local inci- for resection of remnant tissue.6 sional recurrence has rarely been reported. The three most commonly cited indications for thymec- Thymic carcinomas are rare epithelioid malignancies. Thy- tomy are the following: (1) thymic hyperplasia associated mic carcinomas are frequently aggressive tumors that spread with myasthenia gravis7; (2) encapsulated or invasive thymo- both within the pleural space (so-called “drop” metastases) as mas8; and (3) thymic carcinomas.9 Thymic hyperplasia is well as hematogenously. In most cases, the diagnosis is sus- pected on the radiographic studies and confirmed by anterior mediastinotomy. These tumors should be treated with ag- Cleveland Clinic Foundation, Cleveland, Ohio. 9 Address reprint requests to: David P. Mason, MD, Cleveland Clinic Foun- gressive combination therapy. Combined neoadjuvant che- dation, Thoracic and Cardiovascular Surgery, 9500 Euclid Avenue, F24, moradiation therapy followed by aggressive radical surgery Cleveland, Ohio 44195.E-mail: [email protected]. has had only a limited impact on patient survival.

Operative Technique

Figure 1 The thymus gland is derived from the 3rd pharyngeal pouch. The primordia of the thymus gland arises just ventral to the inferior parathyroid gland. The primordial thymic lobes descend caudally and fuse in the midline.13 Ectopic thymus gland can be found along the course of this descent as well as in relation to the parathyroid gland.14 The most common sites of ectopic or variant thymic tissue are (1) indistinct extensions within mediastinal fat (90%)15; (2) extensions lateral to the phrenic nerves (70%)7; (3) extensions into the aortopulmonary window (25%)7; and (4) ectopic thymus in the cervical fat (20%).16,17 Rarely, thymic tissue can be found in a retrothyroid position or posterior to the brachiocephalic vein.7 Radical transsternal thymectomy 233

Figure 2 For anesthetic management, we recommend placement of a double-lumen endotracheal tube for sequential lung isolation. The skin incision for a radical thymectomy can be cosmetically located in the midline. The length of the incision is typically 8 cm, about half the length of the adult sternum (17 to 18 cm). Before sternotomy, skin flaps are mobilized circumferentially. The full-thickness skin flaps are raised superficial to the pectoralis fascia. Perforating vessels are controlled by electrocautery. The mobility of the skin flaps permit comfortable access to the suprasternal notch and the manubrium with the appropriate retraction. 234 D.P. Mason

Figure 3 Retraction of the skin ﬂaps permits a full sternotomy to be performed. The sternotomy facilitates exposure to the inferior mediastinal and cervical fat. A sternal retractor, initially placed in the midline, is moved to facilitate exposure in the appropriate dissection areas. Radical transsternal thymectomy 235

Figure 4 The thymic dissection begins in visible areas of midline pericardium. The dissection is carried cephalad along the pericardium toward the brachiocephalic vein. The dissection is performed with two dental pledgets (cylindrical dental tampon) held by a needle-nosed 11-inch ring handled instrument (Frazier clamp). The cylindrical pledgets facilitate dissection of the pericardial plane while being sensitive to tumor invasion or signiﬁcant adhesions to the pericardium The dissection is completed at the inferior boarder of the brachiocephalic vein. The intervening tissue is the de facto thymic isthmus and is encircled with an umbilical tape. The capsule of the midline thymus is often indistinct. In addition, the midline is a frequent area of ectopic or discontinuous foci of thymic tissue. For these reasons, the entire anterior mediastinal soft tissue from the anterior pericardium to the retrosternal space is included in the specimen. Dissection of the inferior boarder of the brachiocephalic vein invariably reveals the thymic vein near the midline. This vein is transected between silk ties. 236 D.P. Mason

Figure 5 The right-sided dissection begins at the retrosternal pleura and continues posterior to the superior vena cava and right atrium. The pleura is incised to facilitate visualization of the phrenic nerve. In most cases, the pleura is incorporated into the thymic specimen because of adhesions between the thymic gland. The pleura can be left intact if the mediastinal fat and thymic lobe are readily separable from the gland and mediastinal fat and the phrenic nerves have been identiﬁed. Radical transsternal thymectomy 237

Figure 6 The cervical extent of the thymic lobe is dissected bluntly using dental pledgets to facilitate the separation of the thymic horn from the surrounding tissue. The cervical extent of the thymic horn lies medial to the carotid artery and deep to the strap muscles. Surrounding fat should be included in the dissection because of the likelihood of ectopic or accessory thymic tissue.16 During the course of this dissection, arterial blood supply from the internal thoracic artery or inferior thyroid artery may be encountered.18 These branches should be clipped and divided. 238 D.P. Mason

Figure 7 The superior horn of the thymus gland is identified above the thoracic inlet. The cephalad extension of the thymus to the level of the thyroid gland likely reflects its embryologic descent. A leash of small vessels, typically from the inferior thyroid artery, is clipped. The clips provide hemostasis as well as a radiographic marker of the extent of the dissection. The cephalad horn of the thymus is marked with a silk tie and a mosquito clamp. The mosquito is useful because the weight of the instrument is sufficient for retraction without disrupting the delicate cervical extension of the lobe. A similar dissection is performed on the left side. There is no attempt to identify retrothyroid thymic tissue. Radical transsternal thymectomy 239

Figure 8 The inferior extent of the dissection encompasses mediastinal fat from the retrosternal space to the phrenic nerve. The pleura is rarely involved at this level. If adhesions to the pleura or lung are present, the tissue is resected en bloc. The dissection is extended from phrenic nerve to phrenic nerve. Care is taken to avoid injury to the phrenic nerve. Electrocautery is used sparingly. The arterial blood supply arises from the pericardiacophrenic artery bilaterally.18 240 D.P. Mason

Figure 9 The aortopulmonary (AP) window extension of the thymus is only partially visualized from a median sternotomy. Particularly in AP window thymomas, we commonly use complementary thoracoscopic imaging to facilitate an assessment of hilar involvement. Occasionally, large AP window tumors cannot be adequately resected using a median sternotomy. In these cases, we use a hemi-sternotomy combined with an anterior thoracotomy in the 3rd or 4th intercostal space (hemi-clamshell incision). The AP window thymic neoplasms are the most frequent site of phrenic nerve involvement. Tumor involvement of the phrenic nerve requires division of the nerve. If the phrenic nerve is resected, consideration should be given to immediate plication of the diaphragm to limit discoordinate respiratory movement (pendeluft) in the postoperative period. Plication of the central tendon of the diaphragm is particularly important in patients with compromised preoperative lung function. Radical transsternal thymectomy 241

Figure 10 The dotted lines represent the boundaries of the radical, en bloc transsternal resection. 242 D.P. Mason

Figure 11 The incision is drained using two 19 FR Blake drains. One drain is placed in the anterior mediastinum. Occasionally, when a pulmonary resection has been performed as part of the en bloc resection, a separate shortened Blake drain is placed in the pleural space. The sternum is closed using five sternal wires; two wires are placed in the manubrium. A superficial Blake drain is placed beneath the skin flaps to prevent a hematoma from developing in the subcutaneous space. The drains are placed on active suction overnight and usually removed the next morning. Patients are typically discharged from the hospital on postoperative day 3. Radical transsternal thymectomy 243

Conclusion thenia gravis patients: a 20 year review. Ann Thorac Surg 63:853-859, 1996 In the absence of lymphadenopathy, mediastinal invasion, or 5. Roth T, Ackermann R, Stein R, et al: Thirteen years follow-up after radical anatomic ambiguity, we recommend transsternal total thymec- transsternal thymectomy for myasthenia gravis. Do short-term results pre- dict long-term outcome? Eur J Cardiothorac Surg 21:664-670, 2002 tomy of a thymoma without prior biopsy. The transsternal ap- 6. Masaoka A, Monden Y, Seike Y, et al: Reoperation after transcervical proach can be performed with a cosmetically acceptable inci- thymectomy for myasthenia gravis. Neurology 32:83-85, 1982 sion. The superficial skin incision of 7 to 8 cm is comparable to 7. Jaretzki A 3rd, Bethea M, Wolff M, et al: A rational approach to total the aggregate incision of a thoracoscopic approach and the ster- thymectomy in the treatment of myasthenia gravis. Ann Thorac Surg 24:120, 1977 notomy is well tolerated by most patients. More importantly, the 8. Detterbeck FC, Parsons AM: Thymic tumors. Ann Thorac Surg 77: transsternal approach provides sufficient incision and exposure 1860, 2004 to extract the tumor intact for detailed pathologic evaluation of 9. Greene MA, Malias MA: Aggressive multimodality treatment of invasive the thymic capsule and to adequately assess for any local inva- thymic carcinoma. J Thorac Cardiovasc Surg 125:434, 2003 sion. We feel that this approach provides exposure of the neck 10. Beeson, D, Bond AP, Corlett L, et al: Thymus, thymoma, and specific T cells in myasthenia gravis. Ann NY Acad Sci 841:371, 1998 and anterior mediastinum that is superior to a transcervical ap- 11. Wernecke, K, Vassallo P, Rutsch F, et al: Thymic involvement in Hodgkin proach. We recommend transsternal thymectomy for thymo- disease: CT and sonographic findings. Radiology 181:375, 1991 mas that may require a radical resection and for total resection of 12. Loehrer PJ Sr, Wick MR: Thymic malignancies. Cancer Treat Res 105: the observable thymus gland and associated ectopic thymic tis- 277, 2001 13. Gilmour JR: Some developmental anomalies of the thymus and para- sue. thyroids. J Pathol Bacteriol 52:213, 1941 14. van Dyke JH: On the origin of accessory thymus tissue, thymus IV: The occurrence in man. Anat Rec 79:179, 1941 References 15. Morin A, Riou RJ, Fischer L: Various aspects of vascularization of the 1. Nakahara K, Ohno K, Hashimoto J, et al: Thymoma: results with sur- thymus, its vestiges and of the thymic capsule. Arch Anat Pathol (Paris) gical resection and adjuvant postoperative irradiation in 141 consecu- 21:375, 1973 tive patients. J Thorac Cardiovasc Surg 95:1041-1047, 1988 16. Maisel H, Yoshihara H, Waggoner D: The cervical thymus. Mich Med 2. Rehn L: Compression from the thymus gland and resultant death. 74:259, 1975 Excerpts from the transactions of the German Congress of Surgery, 17. Lewis MR: Persistence of the thymus in the cervical area. J Pediatr April 1906. Ann Surg 44:760-768, 1906 61:887, 1962 3. Blalock A, Mason MF, Morgan HJ, et al: Myasthenia gravis and tumors 18. Bell RH, Knapp BI, Anson BJ, et al: Form, size, blood supply and of the thymic region. Ann Surg 110:544-561, 1939 relations of the adult thymus. Q Bull Northwest Univ Med School 4. Masoaka A, Yamakawa Y, Niva H, et al: Extended thymectomy for myas- 28:156, 1954