Most of the mediastinal cysts are benign but still needs surgical excision for
a definitive diagnosis and to prevent compressive symptoms. Radiological
examination itself may sometimes have limited diagnostic value. A pericardial
cyst is always a benign lesion and does not need an excision unless it
reaches to an extreme size while a thymic cyst should be excised when diagnosed
since it may rarely show malignant degeneration. Here we present an
extreme sized thymic cyst radiologically mimicking a pericardial cyst