Role of Thoracic Surgery in Patients with Thymus Gland Pathology

Abstract

Summary T he thymus sits in a central location that puts a number of vital structures at risk during its surgical resection and allows it to be approached from a variety of directions and incisions. Many of the potential complications of thymectomy – phrenic or recurrent nerve injury, bleeding, chylothorax – can be avoided if one has a detailed knowledge of the anatomy of the gland and its relations. Further, the limits of resection for thymic tumors are defined by these critical adjacent structures. The presence of small foci of thymic tissue ectopic to the main body of the gland serves as the pathophysiological basis for the more extensive procedures that have been proposed for thymectomy in MG. Whether the more frequent complications that result from these more extensive operations balance any small improvement in remission rates that may be achieved remains to be seen. Thymus pathology consists of heterogenous groups of diseases. The most common thymus pathology is thymoma. Thymic neoplasms have been recognized more often recently because of increased aggressiveness in evaluating patients with myasthenia gravis. Myasthenia Gravis is an uncommon disease; estimated annual incidence is 2.5 to 20 per million. Prevalence is 50 to 400 cases per million, higher above 40 years. Lifetime risk is 500 per million. The female-to-male ratio is said classically to be 6:4, but as the population has aged, the incidence is now equal in males and females. MG presents at any age, with a bimodal pattern of onset: female incidence peaks in the third decade of life, whereas male incidence peaks in the sixth or seventh decade. Mean age of onset is 28 years in females and 42 years in males. Transient neonatal MG occurs in infants of myasthenic mothers who acquire receptor antibodies via placental transfer of IgG. Some of these infants may suffer from transient neonatal myasthenia due to effects of these antibodies. Rare, nonimmune mediated forms, collectively referred to as congenital MG, may be the result of mutations that adversely affect neuromuscular transmission. Recent advances in treatment and care of critically ill patients have resulted in marked decrease in the mortality rate. The rate is now 3-4%, with principal risk factors being age older than 40 years, short history of severe disease, and thymoma. Previously, the mortality rate was as high as 30-40%. Thymoma is characterized by thymic epithelial cells with variable lymphocytes, subdivided by fi brous bands. Thymic carcinoma lacks features of normal thymus, characterized by cellular atypia, and increased proliferation of cells. Clinical presentation is usually incidental finding, or paraneoplastic syndromes including: endocrine disorders, hematologic disorders and neuromuscular syndromes, e.g., myasthenia gravis (MG) No thymectomy technique appears to achieve unambiguously better results over the other. The difference in complete remission rates between limited and aggressive resections has to be balanced against the immediate risks and the long-term consequences of the surgical procedure. There are different surgical approaches for removal thymus gland pathology which include wide resection of entire thymus from phrenic nerve to phrenic nerve, en bloc resection of invaded structure, and marking residual disease with clips for irradiation if unresectable. Sternotomy approach which is approach of choice for larger thymomas or suspicion of thymic carcinoma. Transcervical thymectomy which is useful for smaller thymomas, via collar incision in the neck. Thoracoscopic thymectomy is a modern, minimally invasive approach to the operative removal of the thymus gland. This technique is just as effective as the above-mentioned conventional surgical techniques. Very low postoperative morbidity, an excellent cosmetic effect, and good early clinical results comparable with those obtained with the conventional methods have resulted in increasing acceptance of the operation by patients and neurologists alike. Thoracoscopic thymectomy therefore represents today in times of minimal invasive treatment first option in the surgical treatment of myasthenia gravis.