Thymic hyperplasia after lung transplantation imitating posttransplant lymphoproliferative disorder

Abstract

Thymic hyperplasia is usually associated with the treatment of malignant tumours and is sometimes linked with endocrine diseases. For the first time, we report a case of thymic hyperplasia in a patient 2 years after bilateral lung transplantation. Contrast-enhanced chest CT scan was highly suspicious for a posttransplant lymphoma or thymoma. Therefore, the patient received total thymectomy. Excised specimens were sent to the Department of Pathology. Unexpectedly, the histological examination revealed hyperplastic thymic tissue without evidence for a posttransplant lymphoproliferative disorder or malignancy.

Figure 1

CT scan of the thorax showing the enlarged mediastinal mass in front of the aortic arch.

Figure 2

(a) Thymic tissue with adjacent mature fat (hematoxylin and eosin, original magnification ×4). (b) Hyperplastic thymus with lobular structure, divorcing fibrous septa, sometimes interrupted by mature fat and enclosed hyperemic vessels (hematoxylin and eosin, original magnification ×4). (c) Thymic tissue with prominent enlarged Hassall's corpuscles (hematoxylin and eosin, original magnification ×20). (d) Immunohistochemistry shows CD20 positivity for B lymphocytes surrounding Hassall's corpuscles (original magnification ×20, methylen blue counterstain). (e) Strong Ki-67 positivity, which demonstrates the high proliferation rate of the cellular elements of thymic tissue. The staining relieves the areas surrounding the Hassall's corpuscles (original magnification ×4, methylen blue counterstain).