MMCTS
(April 25, 2005). doi:10.1510/mmcts.2004.000182
Copyright © 2005 European Association for Cardio-thoracic Surgery
Procedure
Transsternal thymoma resection
Federico Venuta*,
Tiziano de Giacomo,
Claudio Andreetti and
Giorgio Furio Coloni
Department of Thoracic Surgery, Polyclinic Umberto I, University of Rome "La Sapienza", v.le del Policlinico 155, Rome, Italy
* Corresponding author: * Tel.: +39-06-4461971/49970162; fax: +39-06-49970735. E-mail: sofed{at}libero.it
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Summary
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Thymomas are traditionally regarded as tumours arising from the epithelial cells of the thymus. They are the second most frequent mediastinal tumour in the adult and show a variable clinical presentation and clinical course. Complete surgical resection should be the gold standard. The preferred approach is complete median sternotomy and an extended thymectomy is usually performed. A multimodality approach should be considered for invasive lesions or tumours giving intrathoracic metastases.
Key Words: Thymoma • Surgery • Multimodality approach
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Introduction
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Thymic tumours are a heterogeneous group of mediastinal tumours; they include tumours originating from the lymphatic component of the thymus, from the neuroendocrine cells, the stroma and the adipose tissue. However, thymomas are traditionally regarded as tumours arising from the epithelial cells of the thymus. They are the second most frequent mediastinal tumour in the adult and show a variable clinical presentation and clinical course. Thirty percent of the patients are asymptomatic, 30% show local symptoms and 20–40% have systemic symptoms. Twenty to 40% of the lesions are associated to myasthenia gravis and 2 to 5% are associated to red cell aplasia or hypogammaglobulinemia. Thymoma is a disease with many faces; it can appear as a well capsulated lesion located in the anterosuperior mediastinum (Photo 1) or with larger masses more or less capsulated, sometimes with areas of necrosis (Photo 2) or a clear invasive attitude (Photo 3); metastatic spread within the chest (Photo 4) or outside it has been described. The Masaoka staging system (Table 1) is well diffused and helps to describe the aggressiveness of the lesion [1]. It goes from capsulated lesions (stage I) to locally invasive tumours (stage II–III) or neoplasms with metastatic spread (stage IV).
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Photo 2 Lesion of the anterior mediastinum with areas of necrosis; the final diagnosis was stage I thymoma (AB type according to the WHO classification).
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From the histological point of view histogenetic classifications are now widely used [2]; the WHO classification report type A, B and C tumours that progressively show an increased local aggressiveness, tendency to give metastases even after complete resection and to recur (Table 2) [3, 4, 5, 6, 7]. Type A thymoma corresponds to the medullary type of the Marino and Muller-Hermelink classification, type AB to mixed thymoma, type B1 to the predominantly cortical, B2 to the cortical, B3 to well differentiated thymic carcinoma, and type C to the "thymic carcinoma" of the old classification. For these reasons histology and clinical staging should be considered together to assess the therapeutic strategy and prognosis of patients with thymoma.
Complete surgical resection should be the gold standard for patients with thymoma [8, 9, 10]; this goal can be easily achieved for stage I and II tumours that limit their local aggressiveness to the capsula, the surrounding fat tissue and the mediastinal pleura. It may be more difficult to achieve if the tumour invades the surrounding organs (stage III) (superior vena cava, lung parenchyma, pericardium, etc.). In this setting it is important to carefully stage the tumour before surgery; CT and RM are extremely useful; however, sometimes only invasive staging (thoracoscopy, anterior mediastinotomy) can help to ascertain resectability. If complete resection is not feasible induction chemotherapy should be considered [11, 12, 13]. The presence of pulmonary metastasis should not negate the surgical approach; the pulmonary lesion can be excised at the same time if it can be accomplished with a lobectomy or a wedge resection; however, also in this case induction chemotherapy could be a viable option to improve radicality and long-term survival. Postoperative chemo-radiotherapy is employed in many centers both in case of complete or incomplete resection of invasive thymoma [14, 15, 16, 17, 18].
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Surgical technique
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The preferred approach is complete median sternotomy. An anterolateral approach, a lateral or postero-lateral thoracotomy, a clam shell incision or a trap-door approach could be selected on a case by case basis to achieve complete resection; wider exposure is generally required for large tumours extending primarily in one hemithorax or in case bilateral lesions are to be removed.
In case thymoma is not associated to myasthenia gravis (MG) an extended thymectomy is usually performed. If MG is present "maximal thymectomy" as described by Jaretzky is preferred by some authors. Extended thymectomy has been described by Monden in 1985 and is performed by removing "en bloc" the entire thymus, the adjacent fat and any involved structure (Photo 5). The resection usually starts from the upper poles of the gland, if they are recognizable (Video 1); the Keynes veins are isolated and ligated (Video 2) in case a bulky invasive tumour is present, the mass is progressively isolated from the surrounding structures (Video 3); if gross fixation of the tumour to one or more non-vital adjacent structures is present, resection of the adjacent involved tissue should be performed along with the excision of the primary tumour and the residual thymus (Video 4, Photo 6). If the wall of the superior vena cava (SVC) is involved (Photo 7A), tangential resection, patch reconstruction (Photo 7B) with autologous or heterologous pericardium, or complete circumferential excision and replacement with a PTFE prosthesis (Photo 8) should be carried out. When the wall of the aorta or the main pulmonary artery is involved, generally only debulking is performed; however, some authors have described complete resection under cardio pulmonary by-pass (CPBP) with prolonged survival. At the end of the procedure the mediastinum should be completely cleaned with no fat (Video 5). If the mediastinal pleura needs to be incised to enter the thoracic cavity, chest drainages should be placed at the end of the resection; they can be placed through the mediastinum or directly into the chest cavities; subcostal entrance of the tubes may contribute to reduce postoperative pain.
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Photo 5 Operative view at the end of extended thymectomy: the thymus and all the mediastinal fat have been removed.
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Video 1 Thymectomy usually starts from the upper poles of the thymus that are isolated and retracted downward along with the rest of the gland; this improves recognition of anatomy and visualization of the vascular structures of the mediastinum along with their potential involvement.
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Video 2 The Keynes veins are isolated and ligated. They could also be clipped. The left brachiocephalic vein becomes visible and is completely freed from the thymic gland and the mediastinal fat. Also the fat located behind the vein should be removed.
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Video 3 The left and right margins of the tumour are dissected from the surrounding organs. The mediastinal fat should be included in the dissection to obtain complete resection and prevent recurrence.
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Video 4 The mediastinal pleura is involved by the tumour and is resected en bloc with the neoplasm; in this case the lung parenchyma was not infiltrated by the tumour and it was easily separated from the involved mediastinal pleura.
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Photo 6 Operative specimen: a thymoma in the lower pole of the thymus invades the mediastinal pleura resected en bloc with the gland.
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Photo 7 (A) Stage III thymoma invading the superior vena cava and the left brachiocephalic vein. (B) Reconstruction with a patch of autologous pericardium. Reproduced from Venuta F, Rendina EA, Coloni GF. Surgery of the superior vena cava: resection and reconstruction with permission from CTSNet Expert's Techniques.
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Photo 8 Reconstruction of the superior vena cava with a PTFE tube anastomosed to the left brachiocephalic vein. Reproduced from Venuta F, Rendina EA, Coloni GF. Surgery of the superior vena cava: resection and reconstruction with permission from CTSNet Expert's Techniques.
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Video 5 View of the mediastinum at the end of the surgical resection: the gland and the mediastinal fat tissue have been completely removed. The right mediastinal pleura was widely opened. Before closing the chest drainages will be placed in the mediastinum and, if required, in the chest cavity.
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When one phrenic nerve is involved most of the authors recommend excision of the nerve if complete resection is feasible and the patient can tolerate the loss of the function of one hemidiaphragm from the respiratory standpoint. If both phrenic nerves are involved only debulking should be considered. If one phrenic nerve needs to be sacrificed to achieve complete resection, plication of the diaphragm could be performed to reduce lung function loss.
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Results
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Resection of thymoma usually carries a low operative morbidity and mortality. Mortality ranges from a virtual 0% in patients with stage I and II thymic tumours to 10% in case extended resections (SVC or other surrounding structures) have to be performed [19]. Both morbidity and mortality occur more frequently in patients with MG or cardiovascular disorders.
Long-term survival is affected by a number of variables. Completeness of resection, staging and histopathological type seem to be the most important prognostic factors. It is now clear that debulking and non-radical resections are not able to positively influence survival and should be considered like simple biopsy from the oncological point of view. The presence of MG and other paraneoplastic disorders are no longer considered adverse prognostic factors for long-term survival. The new WHO histopathological classification is considered an independent prognostic factor: type A, AB and B1 tumours show a better prognosis (they correspond to the medullary or mixed type of the Marino and Muller-Hermelink classification). B2, B3 and C types show a progressively worse outcome. In particular, type C (thymic carcinoma) should be considered a separate clinical entity with worse prognosis. Also, staging has been repeatedly validated as a strong prognostic factor. Stage I and II thymoma show a long-term survival that exceeds 80–90% at ten years in most of the series. The outcome for stage III and IV lesions is affected by the type of approach. A multimodality approach is now able to favour extended survival also for patients with invasive or metastatic lesion. In particular, the use of induction chemotherapy improves the number of patients receiving complete resection, that is the most important independent factor for long-term survival. Neoadjuvant chemotherapy is usually integrated with postoperative adjuvant administration of radiotherapy and chemotherapy.
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References
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Summary
Introduction
