Glandular enlargement in the mediastinum is usually due to hyperplasia of thymus in the anterior mediastinum or thyroid enlargement with intramediastinal growth. Thymic enlargement is typically due to rebound hyperplasia associated with chemotherapy, radiation therapy, and stresses. Rebound thymic hyperplasia manifests as diffuse, symmetric enlargement of the thymus. MRI may be helpful in distinguishing thymic hyperplasia from neoplastic involvement of the thymus, as the former lose signal on opposed-phase T1-weighted MR imaging. Thyroid goiters may originate in the neck and migrate into the mediastinum or arise from an ectopic focus of mediastinal thyroid tissue. Goiters manifest as mediastinal masses that are similar in appearance to the thyroid gland, with intrinsic hyperdensity, hyperenhancement, foci of calcification and cystic change.
