Atypical pituitary adenoma exhibiting densely secretory granules and basophilia without hormone production

Herein, we report the case of a 46-year-old male patient with only one month of double vision. Radiological examination revealed a pituitary tumor. Endocrinological investigations showed no pathological alterations of anterior pituitary function. Neuropathological examinations revealed a pituitary gland adenoma with an elevated proliferation rate (MIB-1 index 4-5 %) as well as an elevated p53 expression leading to the diagnosis of an atypical pituitary adenoma. Interestingly, the tumor exhibited strong basophilia in routine histology and densely secretory granules in electron microscopy (EM). However, no hormone excess was detectable in immunohistochemistry. In contrast to clinical and immunohistochemical observations, EM and routine histology findings implied a hormone production. This discrepancy might be due to a production of unfunctional pre-stages of pituitary gland proteins in this fast growing neoplasm.