Etiology of Mediastinal Masses Adults In adults, the most common causes vary by location: Anterior mediastinum: Thymomas and lymphomas (both Hodgkin and non-Hodgkin) Middle mediastinum: Lymph node enlargement and vascular masses Posterior mediastinum: Neurogenic tumors and esophageal abnormalities For other causes, see figure Some causes of mediastinal masses in adults.