Fine needle aspiration of thymic epithelial neoplasms and non-neoplastic lesions

Thymic epithelial neoplasms are rare as these tumors represent less than 1% of all human tumors. In addition, thymic hyperplasia and thymic cysts can also present as anterior or less often superior mediastinal masses. Fine needle aspirates and core biopsies of thymic epithelial neoplasms are rarely encountered in routine pathology practices. Histologic classification of these lesions requires microscopic examination of the entire lesion as a significant number of tumors can have more than one histologic type and the status of invasion into adjacent soft tissues or organs is needed for accurate staging. Therefore, it is important to understand the limitations of the information these biopsy methods can provide. The accuracy of the diagnosis can be improved by using ancillary techniques like immunohistochemistry and flow cytometry. In this review, we are summarizing the clinical, histologic and cytologic characteristics of thymic cysts, thymic hyperplasia and thymic epithelial neoplasms including different types of thymoma and thymic carcinoma.