Ann Thorac Surg 2007;83:315-317
© 2007 The Society of Thoracic Surgeons
Case Reports
Ectopic Pleural Thymoma Presenting as a Giant Mass in the Thoracic Cavity
Koji Yamazaki, MD*,
Ichiro Yoshino, MD,
Taro Oba, MD,
Tomofumi Yohena, MD,
Toshifumi Kameyama, MD,
Tetsuzo Tagawa, MD,
Daigo Kawano, MD,
Hidenori Koso, MD,
Yoshihiko Maehara, MD
Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
Accepted for publication March 28, 2006.
* Address correspondence to Dr Yamazaki, Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582 Japan (Email: yamazaki{at}surg2.med.kyushu-u.ac.jp).
 |
Abstract
|
|---|
We describe a rare case of a giant thymoma that developed in the right thoracic cavity, and seemed to originate from the visceral pleura. We believe that there have been few reports of thymoma developing from such an unusual origin.
|
Introduction
|
|---|
Thymoma is an epithelial neoplasm of the thymus, which commonly lies in the anterior mediastinum. Unusually, thymomas can also be found in other locations.
A 58-year-old Japanese woman was referred to us with mild palpitation for a period of 1 month. She presented with mild liver dysfunction in blood chemical tests and a huge, massive shadow on chest roentgenogram. Computed tomography (CT) of the chest demonstrated a giant mass in the lower area of the right thoracic cavity, measuring approximately 20 cm in diameter (Fig 1). On magnetic resonance imaging (MRI), the tumor had a low signal intensity on T1-weighted images and an inhomogeneous signal intensity with fibrous septa on T2-weighted images. The intensity increased inhomogeneously with gadolinium-enhanced T1-weighted imaging. From the CT and MRI findings, the tumorous lesion seemed not to invade the chest wall, but to have some adhesion to the diaphragm or inferior vena cava (Fig 2). Angiography of the right hepatic artery, the right adrenal artery, the right subcostal artery, and the right subclavian artery revealed a number of feeding vessels entering the tumor through the diaphragm, and thus a needle biopsy was not performed.
View larger version (90K):
[in this window]
[in a new window]
|
Fig 1. Enhanced computed tomographic scan at the level of the diaphragm shows a huge inhomogeneous mass and left-side deviation of the lower mediastinum (arrows).
|
|
View larger version (157K):
[in this window]
[in a new window]
|
Fig 2. The T2-weighted frontal magnetic resonance image shows an inhomogeneous mass with compression on the diaphragm, the liver, and the inferior vena cava (arrows).
|
|
Surgical access to the mass was accomplished through a right anterolateral thoracotomy. In the thoracic cavity, a well-defined giant mass measuring 20 x 14 x 8 cm was found to have made expansive growth to adjacent structures without apparent invasion, except for the pulmonary pleura of the right lower lobe and central part of the diaphragm. The tumor was removed completely through a combined resection of the adjacent tissue.
The resected specimen revealed that the tumor was encapsulated with a thin vessel-rich membrane, and the cut surface showed an internal lobulated structure separated by fibrous septa, whitish–yellow in color, and soft in consistency. Microscopic examination of hematoxylin and eosin stained sections revealed polygonal epithelial cells with bland nuclei proliferating in sheets, focally, with cystic change. Immunohistochemical analysis revealed that the tumor cells were diffusely positive for broad-spectrum epithelial keratin (AE1/AE3) and bcl-2, but negative for CD34. Given these histopathologic features, the tumor was consistent with medullary thymoma (type A thymoma according to the World Health Organization classification [1]). The tumor was almost totally encapsulated by fibrous tissue, but it had focally invaded the lung and diaphragm.
Palpitation and liver dysfunction improved immediately after surgery.
|
Comment
|
|---|
Embryologically, the thymic epithelium originates in the third or fourth branchial pouches and descends caudally with the third parathyroid into the anterior mediastinum by the fifth or sixth week of gestation. Aberrant migration may occur anywhere along this pathway and it is believed that ectopic thymomas originate from this aberrant thymic tissue [2]. Seventy-five percent of the thymomas are within the anterior mediastinum, 15% are in both the anterior and superior mediastinum, and 6% are located in the superior mediastinum [3, 4]. The remaining 4% of thymomas occur ectopically, affecting the neck, middle or posterior mediastinum, and lung [5, 6]. However, ectopic thymoma occurring in the pleura is extremely rare and has been infrequently documented [7].
The differential diagnoses for giant intrathoracic mass are a pleural tumor (e.g., solitary fibrous tumor, malignant mesothelioma, and sarcomas), a chest wall tumor, or a metastatic mass. MRI findings of the thymoma have the same or slightly increased intensity as that of muscle on T1-weighted images and increased intensity on T2-weighted images. Inhomogeneous signal intensity on T2-weighted images with a lobulated border, fibrous band, and lobulated internal architecture is indicative of an invasive thymoma [8]. Although the MRI features of this case resembled those of orthotopic thymoma, preoperative diagnosis was difficult because of the unusual location.
In summary, this report documents an extremely rare occurrence of ectopic pleural thymoma presenting as a giant mass in the thoracic cavity.
|
References
|
|---|
- Rosai J, Sobin LH. Histological typing of tumors of the thymus. 2nd ed. New York: Springer; 1999.
- Richardson MA, Sie KYC. The neck: embryology and anatomy. 3rd ed. Philadelphia: WB Saunders Co; 1996.
- Rosai J, Levine GD. Tumors of the thymus. 2nd ed. Washington: Armed Forces Institute Pathol; 1976.
- Detterbeck FC, Parsons AM. Thymic tumors Ann Thorac Surg 2004;77:1860-1869.[Abstract/Free Full Text]
- Moran CA, Suster S, Fishback NF, Koss MN. Primary intrapulmonary thymoma: a clinicopathologic and immunohistochemical study of eight cases Am J Surg Pathol 1995;19:304-312.[Medline]
- Minniti S, Valentini M, Pinali L, Malago R, Lestani M, Procacci C. Thymic masses of the middle mediastinum: report of 2 cases and review of the literature J Thorac Imag 2004;19:192-195.[Medline]
- Moran CA, Travis WD, Rosado-de-Christenson M, Koss MN, Rosai J. Thymomas presenting as pleural tumors: report of eight cases Am J Surg Pathol 1992;16:138-144.[Medline]
- Kushihashi T, Fujisawa H, Munechika H. Magnetic resonance imaging of thymic epithelial tumors Crit Rev Diagn Imag 1996;37:191-259.
Top
Abstract
Introduction
