Hi, Thanks for writing in. The CT scan shows that there is a well defined probably thin walled structure in the mediastinum to the left, the area above the heart. It is a fairly large one measuring 88 x 84 x 60 mm and has fluid contents. This type of a swelling is usually benign and the possibilities which have been provided are a bronchogenic cyst or cystic thymoma. Bronchogenic cyst is a benign fluid containing cyst which has originated from the airway and probably was there since birth. It slowly increased in size. The other diagnosis is a cystic thymoma. The thymus is a tissue which is active in childhood and helps in immunity. Persistent thymus can change to a cystic swelling in some patients. It is suggested to do a FNAC needle test and confirm the nature of the cystic swelling and then proceed to treatment by surgery if required. Please do not worry.