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

Introduction. Thymic enlargement is a rare phenomenon that can be challenging. Materials and methods. 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). Objectives. 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. Results. 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. Conclusion. The two main types of thymic hyperplasia have different pathogenic characteristics and diverse treatment modalities.