True thymic hyperplasia versus follicular thymic hyperplasia: A retrospective analysis of 13 cases

Department of Pathology, Abderrahmen Mami Hospital, 2080 Ariana, Tunisia.
Pathologica 10/2009; 101(5):175-9.
Source: PubMed


Thymic enlargement is a rare phenomenon that can be challenging.
We present a retrospective study over a 13-year period (from 1996 to 2008) of 13 cases of thymic hyperplasia that included 4 cases of true thymic hyperplasia (TTH) and 9 cases of follicular thymic hyperplasia (FTH).
To describe the pathogenesis and different associations of these 2 entities; to emphasize the difficulties in accurate diagnosis without histological examination and to report an unusual association between TTH and cutaneous leishmaniasis.
There were 9 women and 4 men. All patients with FTH had a past medical history of myasthenia gravis (MG). In the group of TTH, 2 patients received chemotherapy and one patient had been administered amphotericin B for a cutaneous leishmaniasis. Radiologic findings showed a mediastinal mass in 7 cases. Thymectomy was performed in all patients with FTH and in one patient with TTH and suspect malignant disease. We observed no complications in any case.
The two main types of thymic hyperplasia have different pathogenic characteristics and diverse treatment modalities.

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    ABSTRACT: Four cases of an unusual type of thymic hyperplasia strongly resembling lymphoepithelial sialadenitis (LESA) of the salivary glands are described. The patients were 2 men and 2 women aged 37 to 53 years. On histologic examination, abundant lymphoid tissue with lymphoid follicles containing germinal centers and areas of plasma cell infiltration were seen. The epithelial component consisted of a proliferation of Hassall corpuscles and islands of thymic epithelial cells. Cystic changes and lymphoepithelial lesions were identified in all cases, but a monocytoid B-cell population was absent. On immunohistochemical examination, a mixed B- and T-cell population was identified, and polymerase chain reaction performed in 1 case showed polyclonality. Follow-up revealed that all patients were alive 5 months to 9 years after diagnosis. The cases in this series represent a distinct type of thymic hyperplasia that histologically strongly resembles LESA. The clinicopathologic and immunohistochemical features are presented, and a possible relationship with thymic mucosa-associated lymphoid tissue (MALT) lymphoma is discussed.
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