The evaluation of a mediastinal mass revolves around the ability to detect the presence of a mass, define its extent and come to a reasonable differential diagnosis. The key is then to use IV contrast (4-5 cc/sec for 100cc of iodixanol) and acquire the images in a rapid acquisition. In most cases a single phase acquisition is satisfactory (usually 30-40 delay) but in other cases two phase acquisition using arterial and venous phase imaging (30-40 second and 70 second delay). Images are acquired with thin and thick sections (< 1mm and 3mm) and reviewed using axial CT and at a minimum multiplanar CT in coronal and sagittal plane. 3D imaging may also prove very valuable especially for defining the vascular map. There are numerous pearls in the evaluation of a suspected mediastinal mass so here are a few we find valuable.

1. There is a wide range of pathologies in the mediastinum ranging from malignant to benign etiologies. The location of a mass to either the anterior, middle or posterior mediastinum is a good place to start. Posterior mediastinal masses are often neurogenic in origin while the anterior mediastinum is the classic 3 T’s and an L (teratoma, thymus, thyroid and lymphoma)
2. The key to anterior mediastinal masses of the is to look for the density of the mass and its enhancement pattern The material composition of the mass (solid vs cystic, presence of calcification or fat) can help identify the etiology of a mass
3. The patient age is important as thymic cysts are more common in younger patients and thymomas more common in older patients
4. Vascularity of the mass may be helpful as teratomas are often very vascular while lymphoma are not.
5. Thymic masses include thymic hyperplasia, thymoma, thymic cyst and thymolipoma. Thymic hyperplasia is often of low CT attenuation and will have a clinical history which helps make the dx.
6. A mass with fat, calcification and soft tissue is most likely a teratoma.
7. Thymic hyperplasia and thymoma are associated with myasthenia gravis.
8. Lymphoma may only involve the anterior mediastinum but other compartments are usually involved and/or additional sites of disease.
9. 3D mapping is especially important in defining vascular involvement by tumors which may be critical for surgical planning.