Thymectomy

Abstract

Thymectomy for MG was first reported by Sauerbruch in 1913 [1]. It became accepted as a therapeutic option for myasthenia gravis after Blalock et al. first performed this procedure in 1936 and described its technique in 1939 [2]. Blalock, who pioneered thymectomy in the management of MG, reported the results of his first six MG patients, who improved after surgical removal of thymus in 1941 [3], and advocated the extension of thymectomy to the treatment of non-thymomatous patients with MG [4]. Keynes in London and Eaton et al. from the Mayo Clinic followed by reporting similarly good results from thymectomy in myasthenic patients [5, 6]. The fact that three-quarters of MG patients have abnormalities of the thymus (commonly hyperplasia of the gland) [7] and one-tenth of patients have thymoma, established the surgical removal of the gland as a popular method in the management of the disease. The introduction of immunosuppressive therapy in conjunction with thymectomy decreased the mortality of the disease from 26% to <5% [8, 9]. A spontaneous remission rate for MG in untreated patients of only 20% [10, 11], compared to reports of complete remission in up to 50% and of clinical improvement as high as 97% after thymectomy, further consolidated the position of surgery as a therapeutic modality for MG. This surgical success led trans-sternal thymectomy to become the "standard" approach. With time, other surgical approaches were introduced; Crile in 1966 introduced the trans-cervical approach [12] and was soon followed by Kirschner et al. [13]. Masaoka et al. in 1975 demonstrated that ectopic thymic tissue could be found in the mediastinal fat of the majority of patients [14]. Following Masoaka's observations Jaretzki and Wolff studied and then described what is now accepted as the normal surgical anatomy of the thymus, defining the findings as "variation" and not "ectopic" (Fig. 9.13). Based on these anatomical findings the "total", later revised to "maximal", thymectomy was developed by Jaretzki [15, 16]. The spectrum of approaches in the modern era of thymectomy now stretches from minimally invasive techniques, such as transcervical and endoscopic approaches, to the "classical" trans-sternal approach with modifications (partial sternotomy), to maximal thymectomy. The computer-assisted matched study of Buckingham et al. [17] found that 33% of patients who underwent thymectomy for MG experienced complete remission, compared to only 8% of those treated medically. The 5- and 10-year survival in myasthenic patients, furthermore, was better with surgery than with medical treatment alone (Fig. 9.1). In a recent meta-analysis of long-term results of thymectomy, 90% of MG patients who underwent surgery improved, 80% became asymptomatic and 50% achieved complete remission [18]. These studies merely established the case for surgery to treat MG. Surgery also became a recognised treatment strategy in the management of thymic enlargement of neoplastic or nonneoplastic origin. When the decision to recommend surgery is made, a thorough pre-operative evaluation and preparation of the patient on a multidisciplinary basis (surgeon, neurologist, radiologist and anaesthetist) is essential (see also chapters 5, 8, 10). Accurate imaging (usually CT or MRI scanning) is of utmost importance to the surgeon, particularly in identifying thymomas and the extent of their invasion locally. This provides the necessary information for designing the surgical strategy. Actual thymic size is of less importance than the relationship of the gland and tumour to adjacent structures, which could predict the possibility of resection and the need for support facilities at the time of surgery, such as cardiopulmonary bypass, cell savers and cardiothoracic anaesthesia. The appropriate preparation of myasthenic patients for thymectomy and their management after surgery needs careful neurological, anaesthetic and intensivist input, and are dealt with in chapters 5, 8, 10 of this book. © Springer-Verlag Berlin Heidelberg 2007.