Fig. 1

Photomicrographs displaying commonly encountered histomorphological features in our cohort. All images are magnified x400 unless otherwise specified. a Hematoxylin-eosin staining of a parathyroid adenoma displaying fibrosis and a focal trabecular growth pattern, two equivocal histological criteria that motivated immunohistochemical analyses. Magnified x100. b Hematoxylin-eosin staining of an atypical adenoma displaying nuclear pleomorphism and macronucleoli. c Hematoxylin-eosin staining of a parathyroid carcinoma displaying vascular invasion. d The intravascular focus was verified by CD31 immunohistochemistry