Ann Thorac Surg 2006;81:1904-1906
© 2006 The Society of Thoracic Surgeons
Case report
Anterior Mediastinal Mass in a Patient With Graves' Disease
Kazuki Yamanaka, MD
a
,
*
,
Haruhiko Nakayama, MD
a
,
Katsuya Watanabe, MD
a
,
Yoichi Kameda, MD
b
a Division of Thoracic Surgery, Kanagawa Cancer Center, Yokohama, Japan
b Division of Pathology, Kanagawa Cancer Center, Yokohama, Japan
Accepted for publication July 26, 2005.
* Address correspondence to Dr Yamanaka, Department of Thoracic Surgery, Yokohama Rosai Hospital, 3211, Kozukue-cho, Kohoku-ku, Yokohama, 222-0036 Japan (Email: kaz-genesis{at}mvb.biglobe.ne.jp).
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Abstract
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Thymic hyperplasia is a common feature in Graves' disease. However, in most cases, thymic enlargement is minimal, and radiologically detectable massive enlargement of the thymus is infrequently reported. Half of them undergo thymectomy due to the concern about a thymoma. We report a 28-year-old woman with untreated Graves' disease. She had an anterior mediastinal mass that was diagnosed as true thymic hyperplasia by biopsy and disappeared after treatment of the hyperthyroid state. Recognizing the association between thymic hyperplasia and Graves'disease, and existence of the benign course after treatment of the hyperthyroidism may be useful for avoiding unnecessary surgical procedure.
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Introduction
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Thymic hyperplasia is a common feature in patients with Graves' disease [1]. In most cases, thymic hypertrophy is minimal and unapparent. Therefore, radiologically detectable thymic enlargement as an anterior mediastinal mass with thyrotoxicosis has been infrequently reported [2]. Half of these cases undergo thymectomy because they are suspected of having thymoma.
In this report, we present a case of an anterior mediastinal mass associated with untreated Graves' disease and describe our approach to this syndrome.
A 28-year-old woman was referred to the Kanagawa Cancer Center for the evaluation of an anterior mediastinal mass in August 2002. She had noticed weight loss with increased appetite, palpitations, hand tremors, and neck swelling 2 months previous to the admission. She had no medical or family history.
Results of physical examination were consistent with findings of typical Graves' disease. The thyroid gland was 3 times as large as the normal one without any focal abnormalities. Results of routine laboratory studies were all normal. Thyroid function tests demonstrated as follows: free T3 to be 16.5 pg/mL (normal range, 2.5 to 4.3), free T4 to be 5.5 ng/dL (normal range, 1.0 to 1.8), and thyroid-stimulating hormone to be < 0.1 u IU/mL (normal range, 0.3 to 4.0). Computed tomographic scan of the chest revealed an anterior mediastinal mass (Fig 1A).
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Fig 1. (A) A contrast computed tomographic scan on admission showed an anterior mediastinal mass with no calcification and no invasion to the neighboring tissue. Size of the mass at presentation was 3.5 x 3 cm. (B) Its size was markedly reduced 3 months after treatment with thiamazole.
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She was treated with 30 mg per day of thiamazole for several weeks and became clinically euthyroid. To determine a definitive diagnosis, the patient underwent biopsy of the thymus gland through a cervical collar incision. The microscopic findings of the specimen demonstrated true thymic hyperplasia (Fig 2).
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Fig 2. Microscopic appearance of the thymus. The proportion of thymic tissue increased with preserving normal structures including cortex, medulla, and Hassall corpuscle. No lymphoid follicle was recognized. (Hematoxylin and eosin; x40.)
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Anti-thyroid medication was continued after the surgery, with keeping a euthyroid state. Three months after surgery, the anterior mediastinal mass disappeared on a repeat computed tomographic scan of the chest (Fig 1B).
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Comment
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Thymic hyperplasia embraces two distinct morphologic forms [3]. True thymic hyperplasia indicates enlargement of the thymus through an increase in the thymic tissue, which remains normally organized. Thymic lymphoid hyperplasia is usually not associated with enlargement of the thymus gland, but refers to the presence of an increased number of lymphoid follicles with germinal centers.
Michie and Gunn [1] report that approximately 38% of patients with thyrotoxicosis have histologic changes of the thymus gland (ie, a simultaneously performed biopsy shows the formation of medullary lymphoid follicles). Thus, histologically, thymic lymphoid hyperplasia is a common feature in patients with Graves' disease. But radiologically detectable massive enlargement of the thymus has been reported in only 22 cases from 15 separate publications. Among these cases, 11 underwent thymectomies and 2 had biopsies. The remaining 9 cases were diagnosed as having thymic hyperplasia due to the clinical progress that the anterior mediastinal mass decreased or disappeared with the medical treatment of hyperthyroidism. Thymic tissues were obtained by thymectomy or biopsy in 13 cases. Among them, 10 have lymphoid follicles and the remaining 3 cases were diagnosed as having true thymic hyperplasia and showed no lymphoid follicles.
The mechanism of thymic hyperplasia in hyperthyroidism is not well established. Van Herle and Chopra [4] described that hyperthyroidism persists after thymectomy, and Scheiff and colleagues [5] reported that administration of triiodothyronine can induce thymic enlargement in mice. Murakami and colleagues [6] investigated thymic size and density in 23 untreated patients with Graves' disease and 38 control subjects using computed tomography. The patients with Graves' disease had larger thymic size and higher thymic density than age-matched control subjects. After treatment with anti-thyroid drugs, both thymic size and density were significantly reduced with a concomitant decrease in thyroid-stimulating hormone receptor antibodies. Murakami and colleagues [6] also clearly showed the presence of thyrotropin receptors in the nonneoplastic thymic tissue by polymerase chain reaction amplification, Northern and Western blot analysis, and immunohistochemistry. These results indicate that thymic hyperplasia is apparently associated with Graves' disease, and suggest that a thymic thyrotropin receptor may act as an autoantigen that may be involved in the pathophysiology of development of Graves' disease.
If an anterior mediastinal mass in a thyrotoxic patient is detected on a computed tomographic scan of the chest, and if it is a homogeneous mass with no invasion to the neighboring tissue, and no calcification, no septum, and no cystic lesion, then a high priority should be given to the treatment of the patient's hyperthyroidism under close radiologic follow-up of the anterior mediastinal mass. If the size of the mass does not decrease in spite of keeping a euthyroid state for several months, we should take minimal invasive diagnostic maneuvers such as a thoracoscopic procedure or a cervical approach.
Recognition of a benign course of thymic hyperplasia in a patient with Graves' disease can avoid a major surgical resection.
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References
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- Michie W, Gunn A. The thyroid, the thymus and autoimmunity Br J Clin Pract 1966;20:9-13.[Medline]
- Budavari AI, Whitaker MD, Helmers RA. Thymic hyperplasia presenting as anterior mediastinal mass in 2 patients with Graves Disease Mayo Clin Proc 2002;77:495-499.[Abstract/Free Full Text]
- Shimosato Y, Mukai K. Tumors of the mediastinum Atlas of tumor pathology. 3rd ed.. Washington, DC: Armed Forces Institute of Pathology; 1997. pp. 26-31fascicle 13..
- Van Herle AJ, Chopra IJ. Thymic hyperplasia in Graves' disease J Clin Endocrinol Metab 1971;32:140-146.[Abstract/Free Full Text]
- Scheiff JM, Cordier AC, Haumont S. Epithelial cell proliferation in thymic hyperplasia induced by triiodothyronine Clin Exp Immunol 1977;27:516-521.[Medline]
- Murakami M, Hosoi Y, Negishi T, et al. Thymic hyperplasia in patients with Graves' diseaseidentification of thyrotropin receptors in human thymus. J Clin Invest 1996;98:2228-2234.[Medline]
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Abstract
Introduction
