Figure 3b-14: Histology of Crooke’s cell adenoma. In these corticotroph adenomas Crooke’s cell change is seen in the tumour cells, rather than non-neoplastic corticotrophs. This is clearly evident in PAS-OG histochemistry, where the hyaline ring displaces the deeply basophilic granules (left). It is also reflected in the dense ring-like cytokeratin pattern (right).