Vividly enhancing soft tissue mass at the left hilum with partial obstructive atelectasis of the left lower lobe and possible post-obstruction pneumonia based on the symptoms.
The triangular enhancing soft tissue mass in the prevascular mediastinum is the thymus and can be considered normal at this young patient's age.
The tubular and slightly hypodense structures next to the pulmonary vessels inside of the atelectasis are mucus-filled and dilated bronchi.