anterior mediastinal mass includes teratoma, thymoma, thyroid, lymphoma

The differential diagnosis for an anterior mediastinal mass includes the "4 T's":

  • thymoma
  • teratoma
  • thyroid neoplasm
  • terrible lymphoma

Within the category of teratoma, one must also include other germ cell tumors. Teratomas can often be distinguished from other germ cell tumors on imaging by the presence of fat or calcium, particularly if in the form of a tooth. Serum hormone levels may be helpful in differentiating seminomatous germ cell tumors from nonseminomatous variants. Serum β-HCG can be elevated in 1/3 of patients with a seminoma, although the AFP is essentially always normal. Nonseminomatous forms of germ cell tumors include yolk sac tumor, choriocarcinoma, and embryonal carcinoma. A mixture of different cell types is also possible and is referred to as a mixed germ cell tumor. Most patients with a nonseminomatous germ cell tumor have an elevated AFP, with a considerable amount also having an elevated β-HCG.

While seminomas often cause an elevated β-HCG, the AFP is essentially always normal.

Lymphomas are the second most common cause of anterior mediastinal mass after thymoma.  They are difficult to distinguish from thymomas on CT scan.  However, lymphomas usually present with systemic B symptoms (eg, fever, night sweats, and weight loss) and extranodal involvement.