4-1. Pituitary gland, rat. (Hematoxylin and Eosin | -400x)
The neoplasm is composed of polygonal cells supported by a fine fibrovascular stroma; neoplastic cells have variably distinct cell borders with moderate amounts of eosinophilic finely granular cytoplasm and irregularly round to oval nuclei with finely stippled chromatin and generally one variably distinct nucleolus.