Background
Thymoma, the most common neoplasm of the anterior mediastinum, originates within the epithelial cells of the thymus.
The thymus is a lymphoid organ located in the anterior mediastinum. In early life, the thymus is responsible for the development and maturation of cell-mediated immunological functions. The thymus is composed predominantly of epithelial cells and lymphocytes. Precursor cells migrate to the thymus and differentiate into lymphocytes. Most of these lymphocytes are destroyed, with the remainder of these cells migrating to tissues to become T lymphocytes. The thymus gland is located behind the sternum in front of the great vessels; it reaches its maximum weight at puberty and undergoes involution thereafter.
History of the Procedure
A relationship between myasthenia gravis (MG) and thymomas was determined incidentally in 1939 when Blalock and coworkers reported the first excision of a thymic cyst in a 19-year-old girl with MG.[1] This patient achieved long-term remission; therefore, thymectomy became the definitive therapy for treatment of generalized MG.
Problem
No clear histologic distinction between benign and malignant thymomas exists. The propensity of a thymoma to be malignant is determined by the invasiveness of the thymoma. Malignant thymomas can invade the vasculature, lymphatics, and adjacent structures within the mediastinum. The 15-year survival rate of a person with an invasive thymoma is 12.5%, and it is 47% for a person with a noninvasive thymoma. Death usually occurs from cardiac tamponade or other cardiorespiratory complications.
Epidemiology
Frequency
Thymoma, the most common neoplasm of the anterior mediastinum, accounts for 20-25% of all mediastinal tumors and 50% of anterior mediastinal masses.
Etiology
The etiology of thymomas has not been elucidated; however, it has been associated with various systemic syndromes. As many as 30-40% of patients who have a thymoma experience symptoms suggestive of MG. An additional 5% of patients who have a thymoma have other systemic syndromes, including red cell aplasia, dermatomyositis, systemic lupus erythematous, Cushing syndrome, and syndrome of inappropriate antidiuretic hormone secretion.
Presentation
Peak incidence of thymoma occurs in the fourth to fifth decade of life; mean age of patients is 52 years. No sexual predilection exists. Although development of a thymoma in childhood is rare, children are more likely than adults to have symptoms. Several explanations for the prevalence of symptoms in children have been proposed, including the following: (1) children are more likely to have malignancy, (2) lesions are more likely to cause symptoms by compression or invasion in the smaller thoracic cavity of a child, and (3) the most common location for mediastinal tumors in children is near the trachea, resulting in respiratory symptoms.
Four cases of patients who presented with severe chest pain secondary to infarction or hemorrhage of the tumor have been reported. Cases of invasion into the superior vena cava resulting in venous obstruction have also been reported.[2] The clinician should be aware of these rare presentations of a thymoma.
Indications
Of patients with a thymoma, one third to one half are asymptomatic, and one third of patients present with local symptoms related to the tumor encroaching on surrounding structures. These patients may present with cough, chest pain, superior vena cava syndrome, dysphagia, and hoarseness if the recurrent laryngeal nerve is involved. One third of cases are found incidentally on radiographic examinations during a workup for MG.
Relevant Anatomy
The thymus gland is located behind the sternum in front of the great vessels and the pericardium. The gland can extend laterally to the phrenic nerves. The main blood supply is from the internal thoracic arteries; however, the thymus gland also is supplied with blood by the inferior thyroid and pericardiophrenic arteries. The anatomy of the thymus is shown in the images below.
Anatomy of the thymus, with emphasis on the blood supply and relation to recurrent laryngeal and phrenic nerves. 
Lateral view: The thymic arteries are derived from the adjacent internal mammary arteries; the inferior thymic vein empties into the innominate vein. The thymus gland's surrounding vascular and neural structures may be invaded during the spread of a thymoma. Contraindications
If the thymoma invades both phrenic nerves, do not resect either nerve; only debulk the area.
Quddus MA, Rahman MM, Ali ZI, et al. Treatment of myasthenia gravis: a surgical profile. Mymensingh Med J. Jul 2009;18(2):203-7. [Medline].
Konstantinov IE, Saxena P, Koniuszko M, Ghosh S, Low VH, Khor TS, et al. Superior Vena Cava Obstruction by Tumour Thrombus in Invasive Thymoma: Diagnosis and Surgical Management. Heart Lung Circ. Apr 9 2007;[Medline].
Bagga S, Bloch EM. Imaging of an invasive malignant thymoma on PET Scan: CT and histopathologic correlation. Clin Nucl Med. Oct 2006;31(10):614-6. [Medline].
Kondo K, Yoshizawa K, Tsuyuguchi M, Kimura S, Sumitomo M, Morita J, et al. WHO histologic classification is a prognostic indicator in thymoma. Ann Thorac Surg. Apr 2004;77(4):1183-8. [Medline].
Falkson CB, Bezjak A, Darling G, et al. The management of thymoma: a systematic review and practice guideline. J Thorac Oncol. Jul 2009;4(7):911-9. [Medline].
Fornasiero A, Daniele O, Ghiotto C, Piazza M, Fiore-Donati L, Calabro F, et al. Chemotherapy for invasive thymoma. A 13-year experience. Cancer. Jul 1 1991;68(1):30-3. [Medline].
Barratt S, Puthucheary ZA, Plummeridge M. Complete regression of a thymoma to glucocorticoids, commenced for palliation of symptoms. Eur J Cardiothorac Surg. Jun 2007;31(6):1142-3. [Medline].
Venuta F, Anile M, Diso D, et al. Thymoma and thymic carcinoma. Eur J Cardiothorac Surg. Jul 15 2009;[Medline].
Shin DM, Walsh GL, Komaki R, Putnam JB, Nesbitt J, Ro JY, et al. A multidisciplinary approach to therapy for unresectable malignant thymoma. Ann Intern Med. Jul 15 1998;129(2):100-4. [Medline].
Loehrer PJ Sr, Wang W, Johnson DH, Aisner SC, Ettinger DS. Octreotide alone or with prednisone in patients with advanced thymoma and thymic carcinoma: an Eastern Cooperative Oncology Group Phase II Trial. J Clin Oncol. Jan 15 2004;22(2):293-9. [Medline].
Wright CD. Pleuropneumonectomy for the treatment of Masaoka stage IVA thymoma. Ann Thorac Surg. Oct 2006;82(4):1234-9. [Medline].
Dango S, Passlick B, Thiemann U, et al. The role of a pseudocapsula in thymic epithelial tumors: outcome and correlation with established prognostic parameters. Results of a 20-year single center retrospective analysis. J Cardiothorac Surg. Jul 15 2009;4(1):33. [Medline]. [Full Text].
Wilkins EW Jr, Grillo HC, Scannell JG, Moncure AC, Mathisen DJ. J. Maxwell Chamberlain Memorial Paper. Role of staging in prognosis and management of thymoma. Ann Thorac Surg. Jun 1991;51(6):888-92. [Medline].
Curran WJ Jr, Kornstein MJ, Brooks JJ, Turrisi AT 3rd. Invasive thymoma: the role of mediastinal irradiation following complete or incomplete surgical resection. J Clin Oncol. Nov 1988;6(11):1722-7. [Medline].
Blumberg D, Port JL, Weksler B, Delgado R, Rosai J, Bains MS, et al. Thymoma: a multivariate analysis of factors predicting survival. Ann Thorac Surg. Oct 1995;60(4):908-13; discussion 914. [Medline].
Wu KL, Mao JF, Chen GY, et al. Prognostic predictors and long-term outcome of postoperative irradiation in thymoma: a study of 241 Patients. Cancer Invest. Jun 22 2009;1. [Medline].
Roviaro G, Rebuffat C, Varoli F, Vergani C, Maciocco M, Scalambra SM. Videothoracoscopic excision of mediastinal masses: indications and technique. Ann Thorac Surg. Dec 1994;58(6):1679-83; discussion 1683-4. [Medline].
Kaiser LR. Thymoma. The use of minimally invasive resection techniques. Chest Surg Clin N Am. Feb 1994;4(1):185-94. [Medline].
Mack M. General Thoracic Surgical Club. La Quinta, Calif: March 1995.
Chilosi M, Zamò A, Brighenti A, Malpeli G, Montagna L, Piccoli P, et al. Constitutive expression of DeltaN-p63alpha isoform in human thymus and thymic epithelial tumours. Virchows Arch. Aug 2003;443(2):175-83. [Medline].
Detterbeck FC, Parsons AM. Thymic tumors. Ann Thorac Surg. May 2004;77(5):1860-9. [Medline].
Engels EA, Pfeiffer RM. Malignant thymoma in the United States: demographic patterns in incidence and associations with subsequent malignancies. Int J Cancer. Jul 1 2003;105(4):546-51. [Medline].
Fujiwara T, Mizobuchi T, Shibuya K, Hiroshima K, Fujisawa T, Iwai N. Rapid regression of stage IVb invasive thymoma under palliative corticosteroid administration. Gen Thorac Cardiovasc Surg. Apr 2007;55(4):180-3. [Medline].
Giaccone G. Treatment of malignant thymoma. Curr Opin Oncol. Mar 2005;17(2):140-6. [Medline].
Hassantash SA, Ashbaugh DG, Verrier ED, Maier RV. Surgical treatment of myasthenia gravis in two major Middle East teaching hospitals: factors influencing outcome. Thorax. Feb 1996;51(2):193-6. [Medline].
Henley JD, Cummings OW, Loehrer PJ. Tyrosine kinase receptor expression in thymomas. J Cancer Res Clin Oncol. Apr 2004;130(4):222-4. [Medline].
Kohman LJ. Controversies in the management of malignant thymoma. Chest. Oct 1997;112(4 Suppl):296S-300S. [Medline].
Luketich JD, Ginsberg RJ. The current management of patients with mediastinal tumors. Adv Surg. 1996;30:311-32. [Medline].
Mullen B, Richardson JD. Primary anterior mediastinal tumors in children and adults. Ann Thorac Surg. Sep 1986;42(3):338-45. [Medline].
Okumura M, Ohta M, Tateyama H, Nakagawa K, Matsumura A, Maeda H, et al. The World Health Organization histologic classification system reflects the oncologic behavior of thymoma: a clinical study of 273 patients. Cancer. Feb 1 2002;94(3):624-32. [Medline].
Rivner MH, Swift TR. Thymoma: diagnosis and management. Semin Neurol. Mar 1990;10(1):83-8. [Medline].
Thomas CR, Wright CD, Loehrer PJ. Thymoma: state of the art. J Clin Oncol. Jul 1999;17(7):2280-9. [Medline].
Wright CD, Wain JC. Acute presentation of thymoma with infarction or hemorrhage. Ann Thorac Surg. Nov 2006;82(5):1901-4. [Medline].
| Type | Histologic Description | Disease-Free Survival at 10 years*, % |
| A | Medullary thymoma | 100 |
| AB | Mixed thymoma | 100 |
| B1 | Predominantly cortical thymoma | 83 |
| B2 | Cortical thymoma | 83 |
| B3 | Well-differentiated thymic carcinoma | 35 |
| C | Thymic carcinoma | 28 |
| *Series of 100 thymomas resected in Japan between 1973 and 2001 using the WHO classification. | ||
| Stage | Definition | Treatment |
| I | Encapsulated tumor with no gross or microscopic invasion | Complete surgical excision |
| II | Macroscopic invasion into the mediastinal fat or pleura or microscopic invasion into the capsule | Complete surgical excision and postoperative radiotherapy to decrease the incidence of local recurrence |
| III | Invasion of the pericardium, great vessels, or lung | Complete surgical excision and postoperative radiotherapy to decrease the incidence of local recurrence |
| IVA | Pleural or pericardial metastatic spread | Surgical debulking, radiotherapy, and chemotherapy |
| IVB | Pleural or pericardial metastatic spread | Surgical debulking, radiotherapy, and chemotherapy |
| Stage | 5-Year Survival | 10-Year Survival |
| I | 90% | 80% |
| II | 90% | 80% |
| III | 60% | 30% |
| IV | Less than 25% | N/A |
Print
