Figure 15. (a) Thyrotroph hyperplasia in a patient with primary hypothyroidism retains acinar architecture but the expanded acini are dominated by large cells with pale cytoplasm; a few smaller acidophils and basophils are identified (arrow). (b) The large “thyroidectomy” cells have abundant cytoplasm with scattered PAS-positive globules (large arrows); the PAS stain also identifies corticotrophs (short arrows).