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Ann Thorac Surg 1998;66:2106-2108
© 1998 The Society of Thoracic Surgeons
a Department of Thoracic Surgery, Guy’s Hospital, London, United Kingdom
b Department of Histopathology, Guy’s Hospital, London, United Kingdom
Accepted for publication June 1, 1998.
Address reprint requests to Mr Dussek, Department of Thoracic Surgery, Guy’s Hospital, St. Thomas Street, London SE1 9RT, UK
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Abstract |
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Introduction |
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A 50-year-old white man presented with a cough productive of sputum and weight loss of about 10 kg over 1 year. Thirty-two years previously he had a mediastinal mass on routine chest x-ray. Although he was asymptomatic at the time, he underwent excision of this mass through a transsternal incision. Excision of the tumor was described as complete, and histologic analysis revealed a cortical thymoma (according to the Muller-Hermelink criteria). The thymoma was encapsulated with no evidence of malignancy or invasion (Masaoka stage I). The patient developed myasthenia gravis 26 years after the operation and was treated with prednisolone, azathioprine, and pyridostigmine. He remained well for the next 4 years; chest x-rays and computed tomographic scan of the thorax were normal during this period.
Apart from generalized weakness of myasthenia gravis there were no other abnormalities on examination. Results of blood investigations were normal. Chest x-ray and computed tomographic scan of the thorax now revealed a mediastinal mass in close apposition to the left border of the heart. This mass was assumed to be a recurrence of the old thymic tumor, and the patient underwent further operation.
Through a left thoracotomy, a yellow mass was observed between the pericardium and the upper lobe of the left lung, with direct invasion of both structures. Surgical excision of the mass with left upper lobe and adherent pericardium was performed. Histological examination of the mass found, as before, a cortical thymoma, but now with invasion of lung parenchyma and subpericardial fibrous and adipose tissue. One mediastinal lymph node was replaced by tumor (Masaoka stage IVa).
The postoperative recovery was uncomplicated, and the patient was discharged on the sixth postoperative day. The patient had three courses of chemotherapy 3 months postoperatively. The regimen was a combination of cyclophosphamide, adriamycin, and cisplatin. At 12 months follow up, the patient was alive with improved symptoms of myasthenia gravis.
The specimen excised 32 years previously was retrieved and reexamined. We confirmed a cortical thymoma with no evidence of malignancy (Fig 1). The recurrent tumor is shown in Figure 2 and reveals some similarities with the original tumor.
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Comment |
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The overall rate of recurrence of thymoma is approximately 20%. The recurrence rate is related to the clinical stage (being lowest for stage I disease) and cellular differentiation. There is increased malignant potential and recurrence rate if cells are cortical rather than medullary [2] and predominantly epithelial rather than lymphocytic [3]. The recurrence rate is also higher (31% compared with 11%) and the prognosis is worse in the patients without myasthenic thymoma than in those with myasthenic thymoma [4]. These differences might result from the earlier diagnosis of thymoma in patients with myasthenia gravis and the initiation of treatment before microscopic spread has occurred. The presence of myasthenia gravis has been shown not to affect survival in patients with thymoma, if the treatment of the myasthenia gravis was improved [5].
Total excision alone appears to be inadequate treatment, resulting in unacceptably high recurrence rates for thymomas of stage II and greater. In contrast, total excision of stage I thymoma is accepted as the sole treatment by many surgeons. The overall survival, at 10 years after operation alone, is approximately 80% for noninvasive and 35% for invasive thymoma. Independent predictors of survival are similar to those of recurrence (histology, tumor size, stage of disease, and extent of surgical excision) [6].
In the present case, it is possible that the primary thymoma was not completely excised at initial operation, and the recurrent thymoma could have been a malignant change or even a new primary in residual or ectopic thymic tissue. Masaoka and colleagues [1] identified the frequent existence of thymic tissue in anterior mediastinal adipose tissue around the thymus and advocated extended thymectomy (excision of thymus and mediastinal adipose tissue) for the treatment of myasthenia gravis, in both thymomatous and nonthymomatous patients. This suggests that excision of thymoma alone, even if stage I disease, is inadequate and that to minimize recurrence or the development of a new primary, extended thymectomy should be undertaken.
Postoperative radiation therapy is effective in preventing recurrence but even after whole mediastinal irradiation, recurrence could occur in the pleural cavity. Extended radiation fields including the entire hemithorax have thus been recommended after incomplete excision of thymoma and in invasive thymoma. Thymomas are also chemosensitive and combination chemotherapy is effective in the first-line postoperative treatment of incompletely excised thymoma and also in the treatment of local or metastatic relapses after chemotherapy [7].
Myasthenia gravis developed in this patient 26 years after the initial excision of the thymoma, and the recurrence was diagnosed on computed tomographic scan another 6 years later. A computed tomographic scan of the thorax taken 2 years before the recurrent thymoma was diagnosed was reported as normal. This finding is interesting but not unusual. Namba and coworkers [8] showed that most patients who develop myasthenia gravis after excision of thymomas were found not to have residual thymus at postmortem examination or at reoperation.
All thymomas appear to have malignant potential. In addition, noninvasive thymomas (particularly cortical thymomas) can recur many years postoperatively (as in this case), even if thought to be completely excised. Therefore, extended thymectomy, to include mediastinal adipose tissue, should be undertaken in all patients with thymoma, and these patients should be followed up for life.
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