Does a chest x ray reveal enlarged lymph nodes in neck area such as under the thymus gland caused by lymphoma?

Chest X-ray. : A chest X-ray would not be a reliable test in this regard.

The thymus gland: is not in the neck, it is in the chest(anterior mediastinum). If the lymph nodes get large enough, the chest xray will be abnormal. However, a chest xray is not a reliable way to rule out adenopathy, because the lymph nodes have to get quite bulky to show up. CT is a much more sensitive and specific test for mediastinal adenopathy.