PMC4590429_01
The chest computed tomography showed a large anterior mediastinal cystic mass lateralized to the left side frame evoking a cystic teratoma or a cystic thymoma without aggressive loco-regional signs (arrow).
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The chest computed tomography (CT) scan showed a large anterior mediastinal cystic mass lateralized to the left side frame evoking a cystic teratoma or a cystic thymoma without aggressive loco-regional signs (Figure 1).
Gross examination showed a unilocular cystic mass (arrow) with some thymic lobules (star).
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Gross examination showed a cystic mass of 7 cm, thin-walled with brownish liquid content (Figure 2).
Microsopic findings.. Notes: (A) The coexistence of a cystic lesion (arrow) and true thymic hyperplasia (hematoxylin and eosin stain [HE] x250; (B) the epithelial lining (arrow) of the cyst was mainly flattened and focally hyperplastic (HE x400); (C) true thymic hyperplasia is characterized by the conservation of the thymic architecture which consists of a corticomedullary differentiation and the presence of many Hassall's corpuscles in the medulla (HE x250); (D) immunohistochemical study showing the positivity of the lymphocytes with the terminal deoxynucleotidyl transferase antibody (HE x250); (E) immunohistochemical study showing the positivity of the epithelial lining with the cytokeratin antibody (HE x250).
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Microscopic examination showed a cyst wall lined by a flattened and unistratified epithelial lining overcoming thymic residues (Figure 3). Thymic parenchyma seemed hyperplastic with conservation of the corticomedullary differentiation with the presence of many Hassall's corpuscles (Figure 3).