Pituitary tumours are also classified according to their immunological and histochemical staining characteristics (Fig. 2.3). Since interpretation of tumour sections may be extremely subjective using the haematoxylin and eosin (H and E) stain, current practice is to use the periodic acid Schiff-orange G (PAS-OG) stain. Evaluation of the size of the intracellular granules by electron microscopy is also useful since prolactin- and GH-secreting adenomas have the largest intracellular granules (the prolactin granule has a mean diameter of 550nm).
