Video - Thymus histology

The thymus is a flat encapsulated lymphoid organ located behind the sternum. It's most active during childhood and slowly involutes in adulthood, with fatty infiltrates and decreased thymic tissue. The thymus gland has two lobes, each of which has an outer cortex that's very basophilic and stains dark purple, whereas the inner medulla stains a lighter purple and pink color. The cortex consists of many basophilic T lymphoblasts that are supported by a meshwork of thymic epithelial cells (TECs), which have a pale cytoplasm with cytoplasmic processes. The inner medulla also has an abundance of TECs, but will also contain Hassall's corpuscles, which are the structures formed by closely packed and concentrically arranged TECs.