Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Heart size remains normal . Mediastinal contours are remarkable for a focal convexity of the left upper mediastinal contour just above the level of the aortic knob . Review of prior CTA of the chest of ___ demonstrates a focal soft tissue abnormality in this region , possibly related to the thymus gland . Lungs and pleural surfaces are clear , and there are no acute skeletal findings .
    OUTPUT:
    
Focal left mediastinal contour abnormality , which may correspond to an area of thymic tissue on previous CTA of the chest of ___ . It is uncertain whether this represents asymmetrical residual thymus tissue or a thymic epithelial neoplasm . Recommend a chest CT to allow more accurate comparison to the prior CT of the chest of ___ , as entered into the radiology communications dashboard on ___ .