Ann Thorac Surg 2004;77:2209-2210
© 2004 The Society of Thoracic Surgeons
Case report
Noninvasive thymoma in the middle mediastinum
Masato Kanzaki, MD, PhDa*,
Kunihiro Oyama, MD, PhDa,
Toyohide Ikeda, MD, PhDa,
Tamami Yoshida, MDa,
Masahide Murasugi, MD, PhDa,
Takamasa Onuki, MD, PhDa
a Department of Surgery I, Tokyo Women's Medical University, School of Medicine, Tokyo, Japan
Accepted for publication June 3, 2003.
* Address reprint requests to Dr Kanzaki, Department of Surgery I, Tokyo Women's Medical University, School of Medicine, 8-1 Kawad-cho, Shinjuku-ku, Tokyo 162-8666, Japan
e-mail: kanzaki{at}chi.twmu.ac.jp
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Abstract
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We present a rare case of thymoma that developed entirely in the middle mediastinum. A 60-year-old woman was referred to our hospital with a mediastinal mass. The mass was located in the visceral compartment of Shields' mediastinal classification. Intraoperative pathologic evaluation revealed a thymoma, whereupon total thymectomy was performed. The postoperative course was uncomplicated and the patient received no postoperative adjuvant radiotherapy.
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Introduction
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Thymoma is the most common primary neoplasm of the anterior mediastinum, although it can also arise in other locations: the neck, the middle or posterior mediastinum, the lung, and the pleural cavity. Ectopic thymomas are considered to arise from distributed thymic tissues and as a result of failure to migrate into the anterosuperior mediastinum. Thymoma should be considered in the differential diagnosis of visceral compartment tumors. Despite complete resection, noninvasive thymoma may recur postoperatively. Therefore, extended thymectomy should be undertaken in all patients with noninvasive thymoma.
A 60-year-old woman was referred to our hospital with a mediastinal mass detected by chest roentgenogram during a routine medical check-up and confirmed in subsequent computed tomography (CT) scan. She denied any symptoms. Physical examination and laboratory work-up were within normal limits. Contrast-enhance CT revealed a solitary and nonhomogeneously enhanced calcified mass, 6 cm in maximum diameter, in the middle mediastinum, between the superior vena cava (SVC) and the ascending aorta (Ao; Fig 1).
Magnetic resonance imaging revealed a loburated the middle mediastinal mass. The mass demonstrated a low intensity on the T1-weighted image, and a slightly high intensity on the T2-weighted image. A benign teratoma, giant lymph node hyperplasia, or noninvasive thymoma was suspected. We undertook surgical intervention without preoperative diagnosis. Median sternotomy was performed. Tumor was below the junction of bilateral innominate veins. Separating the SVC and the Ao, the right main pulmonary artery was retracted inferiorly, the tumor (6.0 x 5.5 x 4.1 cm) was solid and elastic with a capsule and easily extracted. The mass was contiguous to the adipose tissue surrounding the thymus at the retroinnominate vein area. Intraoperative pathologic evaluation found a thymoma and then a total thymectomy was performed. The resected specimen revealed a thymoma with the capsule composed of dense fibrous tissue with some residual adipose and thymic tissue with foci of calcification. Microscopic examination indicated spindle cells with round to oval nuclei were arranged in a whorled pattern and lymphocytes were scattered among them (Fig 2).
Histopathologic appearance of the tumor showed predominantly spindle cell thymoma (type AB, the World Health Organization classification) and the pathologic stage was stage I (the classification of Masaoka) [1, 2]. The postoperative course was uncomplicated. Postoperatively, she received no adjuvant radiotherapy.
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Fig 1. Enhanced computed tomography revealed a solitary and nonhomogeneously enhanced calcified mass in the middle mediastinum, between the superior vena cava and the ascending aorta.
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Fig 2. Histopathologic findings were predominantly spindle cell thymoma (Hematoxylin& eosin stain; original magnification, x200).
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Comment
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The mediastimun is tightly packed with intertwined organs and conduits. Shields' three-compartment model is the most accurate anatomic representation of the mediastinum, which consists of an anterior compartment, a visceral compartment, and the bilateral paravertebral sulci. The visceral compartment of Shields' mediastinal classification contains the heart, pericardium, and the major vessels leaving and entering this organ; the trachea and main bronchi; lymph nodes (paratracheal and tracheobronchial); and the phrenic and vagus nerves. Thymic lesions are found in the anterior compartment. Rarely, ectopic thymic tissue is present in the retroinnominate vein area and in the adipose tissue surrounding the thymus [3, 4]. Ectopic thymomas are considered to arise from distributed thymic tissues and as a result of failure to migrate into the anterosuperior mediastinum [5–7]. Thymomas can also be located in the middle mediastinum, as in the present case. To our knowledge, however, middle mediastinal thymoma has previously been reported in only one case in the literature [7].
If the tumor is mediastinal, the next question concerns the need for biopsy. Not all mediastinal masses require preoperative diagnosis, which is preferred for small and well-delineated lesions that on CT examination appear to be amenable to complete resection. Indeed in certain tumors, such as thymomas, cells shed from the tumor might implant in the adjacent mediastinal structures.
Thymomas appear to have malignant potential. The overall rate of recurrence of thymoma is approximately 20%. Complete surgical resection is the cornerstone of therapy for encapsulated thymomas and is usually curative. For patients with encapsulated (stage I) thymomas, the role of adjuvant radiation therapy has not been defined [8]. Despite complete resection, noninvasive thymoma may recur postoperatively. Extended thymectomy, to include the mediastinal adipose tissue and the retroinnominate vein area, should be undertaken in all patients with noninvasive thymoma.
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References
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- Rosai J. Histological typing of tumors of the thymus. World Health Organization: International Histological Classification of Tumours, 2nd ed Berlin: Springer, 1999:9-15.
- Masaoka A., Monden Y., Nakahara K., Tanioka T. Follow-up study of thymomas with special reference to their clinical stages. Cancer 1981;48:2485-2492.[Medline]
- Ashour M. Prevalence of ectopic thymic tissue in myasthenia gravis and its clinical significance. J Thorac Cardiovasc Surg 1995;109:632-635.[Abstract/Free Full Text]
- Carr C.S., O'Keefe P.A. An ectopic thymoma with spontaneous infarction. J Thorac Cardiovasc Surg 2001;122:1234-1235.[Free Full Text]
- Fukai I., Funato Y., Mizuno T., Hashimoto T., Masaoka A. Distribution of thymic tissue in the mediastinal adipose tissue. J Thorac Cardiovasc Surg 1991;101:1099-1102.[Abstract]
- Jaretzki A., 3rd, Wolff M. "Maximal" thymectomy for myasthenia gravis. Surgical anatomy and operative technique. J Thorac Cardiovasc Surg 1988;96:711-716.[Abstract]
- Kojima K., Yokoi K., Matsuguma H., et al. Middle mediastinal thymoma. J Thorac Cardiovasc Surg 2002;124:639-640.[Free Full Text]
- Monden Y., Nakahara K., Iioka S., et al. Recurrence of thymoma: clinicopathological features, therapy, and prognosis. Ann Thorac Surg 1985;39:165-169.[Abstract]
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Abstract
Introduction
