List six causes of a middle mediastinal mass.

1.Lymphadenopathy caused by sarcoidosis, lymphoma, infection, or neoplasm
2. Bronchogenic carcinoma
3. Hiatal hernia, usually near the gastroesophageal junction
4. Aortic aneurysm
5. Thyroid mass extending down from the neck
6. Bronchogenic cyst, usually near the carina