Answer:
The thymus appears as a soft tissue mass in the anterior mediastinal space on a chest X-ray. It can have a triangular, rectangular, or rounded shape. In infants and children, it is usually well-defined and can be quite large, sometimes occupying a significant portion of the chest cavity. In adolescents and adults, the thymus often shrinks and may become more difficult to see on a chest X-ray, often replaced by fatty tissue.