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J Thorac Cardiovasc Surg 1994;107:1169-1171
© 1994 Mosby, Inc.

LETTERS TO THE EDITOR

A symptomatic thymic cyst in the middle mediastinum

R. J. van Klaveren, MD, J. Festen, MD, L. K. Lacquet, MD, J. M. Wiersma-Tilburg, MD, A. L. Cox, MD

University Hospital Nijmegen
Nijmegen, The Netherlands

To the Editor:

Thymic cysts are uncommon and represent 1% to 2% of mediastinal cysts and tumors. They usually remain asymptomatic, are found on routine chest roentgenograms, and are located in the neck or anterior mediastinal compartment. Go 1 To our knowledge, this is the first report of a symptomatic thymic cyst located in the middle mediastinum.

In 1991, a 60-year-old man was referred to our clinic because of dyspnea on effort, hoarseness, and a vague sense of chest pain. Physical examination showed only prolonged expiration. Laboratory investigations were normal. The chest roentgenogram appeared normal other than an elevated right hemidiaphragm with partial limited movement on x-ray examination. Lung function tests showed an expiratory air-flow obstruction without improvement after salbutamol inhalation. Results of skin tests were negative, the provocative concentration of histamine causing a 20% fall in FEV1 (forced expiratory volume in 1 second) was 4 mg/ml (normal, >8 mg/ml). The diagnosis of chronic obstructive pulmonary disease was made. Despite treatment with budesonide, the patient's condition did not improve. Reevaluation of the breath sounds several months later revealed prolonged and wheezing inspiration and expiration.

On examination with a bronchoscope, an immobile left vocal cord and compression from anterior of the main carina and the left main bronchus, with more than 50% reduction of the diameter, were seen. The mucosa appeared normal. A computed tomographic scan showed a smooth, solitary mass (4.5 x 5.9 cm, 26 Hounsfield units), with well-defined margins in the middle mediastinum with compression of the carina, the left main bronchus, and the pulmonary artery from the ventral side (Fig. 1). With the preliminary diagnosis of bronchial cyst, the patient was operated on. A cyst with a sterile, green, blistering mucoid content was removed. There was no relationship with the bronchus or the esophagus, but the lesion was in the near vicinity of the recurrent laryngeal nerve under the aortic cross. After thoracotomy, the patient had prompt relief of his dyspnea. His hoarseness improved as well. Pathologic examination showed a pseudocyst with a smooth, exterior, fibrous capsule. The cyst had a greenish, blistering mucoid content and signs of an old hemorrhage. Microscopic examination of the capsule showed no epithelial lining, smooth muscle, or cartilage. The mucoid fluid of the cyst contained cholesterol crystals and cholesterol granulomas. These findings were consistent with a thymic cyst (Fig. 2).



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  		Fig. 1. Computed tomographic scan of the thorax shows a mass (4.5 to 5.9 cm, 26 Hounsfield units) in the middle mediastinum with compression of the main carina (arrow)and left pulmonary artery (arrowhead).

 


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  		Fig. 2. Content of the cyst showing cholesterol crystals and cholesterol granulomas. (Hematoxylin and eosin stain; x400.)

 
Mediastinal thymic cysts occur predominantly in the second to fifth decades of life and are almost always asymptomatic, Go 1 although dyspnea, cough, and chest pain have been described. Go Go 2,3 Radiologically, these lesions appear as smooth, circumscribed masses in the anterosuperior mediastinum, with a density approximating that of water in most cases. Go 4 Location in the middle mediastinum is atypical, but in a recent study on the distribution of thymic tissue in mediastinal adipose tissue in autopsy subjects, histologically proven thymic tissue was found in the anterior mediastinal fat in 44.4%, in the retrocarinal fat in 7.4%, and in the preaortic fat in 0%. Go 5 The existence of ectopic thymic tissue in the retrocarinal fat makes location of thymic cysts in the middle mediastinum possible.

The histopathologically confirmed presence of cholesterol granulomas and the absence of bronchus-type epithelial lining, smooth muscle, or cartilage is a specific feature of thymic cysts that excludes the possibility of other cystic lesions, such as bronchogenic cysts. Go 6 Remnants of thymic tissue, including Hassall's corpuscles, can only be seen in about 50%. Degeneration of Hassall's corpuscles can result in cholesterol granulomas and crystals. The absence of corpuscles therefore does not exclude the diagnosis of thymic cyst. Go 6

References

  1. Ovrum E, Birkeland S. Mediastinal tumours and cysts: a review of 91 cases. Scand J Thorac Cardiovasc Surg 1979;13:161-8.[Medline]
  2. Joob A, Shields TW. Mesothelial and other less common cysts of the mediastinum. In: Shields TW, ed. Mediastinal surgery. Philadelphia: Lea & Febiger, 1991:325-35.
  3. Leong ASY. Thymic cysts. In: Givel JC, ed. Surgery of the thymus. Berlin: Springer-Verlag, 1990:71-7.
  4. Schnyder P, Gamsu G. Computed tomography and magnetic imaging. In: Givel JC, ed. Surgery of the thymus. Berlin: Springer-Verlag, 1990:217-25.
  5. Fukai I, Funato Y, Mizuno T, Hashimoto T, Masaoka A. Distribution of thymic tissue in the mediastinal adipose tissue. J THORAC CARDIOVASC SURG 1991;101:1099-102.[Abstract]
  6. Wick MR. Mediastinal cysts and intrathoracic thyroid tumors. Semin Diagn Pathol 1990;7:285-94.[Medline]



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S. Numata, W. M. M. Aye, and C. N. Lee
Cardiac herniation after resection of pericardial thymic cyst
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[Abstract] [Full Text] [PDF]

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