[Clinical case : Prevascular mediastinal mass].

In the event of a prevascular mediastinal mass, knowledge of the anatomy and content of the mediastinum is an essential prerequisite to establish a differential diagnosis. The «4T» rule is applicable because it is a simple and effective mnemonic. It groups together; thyroid goiter, terrible lymphoma, teratoma and thymoma. The reference imaging technique is computed tomography with injection of iodinated contrast media, allowing the analysis of the lesion as well as its topography and its relationship with adjacent structures. Concerning the case of a lymphoma, PET/CT is the reference examination, as it allows a precise assessment of extension and can establish a target lesion for excisional biopsy which will make the definitive diagnosis. PET/CT is also used for therapeutic monitoring.