AB 33. Tumor-like cystic lesion of the thymus: thymic cyst. Case report

Background: Thymic cysts are rare lesions, and are most likely congenital. They are found along the anatomic course of embryologic descent of the thymus from the third pharyngeal pouch. In the mediastinum, the cysts are very often asymptomatic and found accidentally by chest-x-ray examination in the adults. We describe the case of thymic cyst in a 75 year-old asymptomatic man, who presented with a tumor-like cystic lesion of the thymus apparent accidentally by chest-x-ray and CT scan. The tumor like lesion was excised.
Patients and methods: The surgical specimen was well circumscribed fatty tissue with white areas and a cystic formation measuring 4.6 cm × 4 cm× 4 cm.
Results: Histological examination showed fibrous thin walled cyst with attached fatty thymic tissue and linning by a single layer or multilayer of cuboidal and columnar cells.
Conclusions: It is essential to find thymic tissue in the wall of the cyst in order to establish a diagnosis of thymic cyst and it may by necessary to examine multiple sections of the cyst wall. The differential diagnosis includes cystic thymoma, cystic teratoma and other mediastinal cysts. Malignant transformation is rare.