BACKGROUND AND OBJECTIVE: Incidence of thymic lesions in the form of mediastinal cyst is very rare and is accompanied by risk of malignancy, which may induce signs of compression in mediastinum or accidentally be found during imaging. A case of mediastinal thymic cyst with compression-induced shortness of breath is presented.

CASE REPORT: A 40 year old woman underwent diagnostic assessment because of shortness of breath. Considering imaging results regarding upper mediastinal cystic lesion with possible origin of thymus, she underwent excision of mass and middle sternum. Histopathologic examination reported a simple thymic cyst.

CONCLUSION: Considering respiratory problems of patients with mediastinal cystic lesion, timely diagnosis and treatment is necessary to prevent probable malignancy in addition to relieving symptoms.