Null Cell Adenoma of the Pituitary: Pseudo-rosettes Say It Best When Immunohistochemistry Says Nothing At All!

Null cell adenoma is composed of adenohypophyseal cells that show no evidence of any specific cell type differentiation by immunohistochemistry or transcription factors like pituitary-specific positive transcription factor 1 and steroidogenic factor 1. Though rare, pituitary ependymoma and germinoma are also known to occur at sellar region and in such instances, it is challenging to differentiate them from a pituitary null cell adenoma featuring papillary architecture and perivascular pseudo-rosettes. We describe a case of an elderly diabetic lady presenting with headache and blurring of vision for past 3 months due to a sellar tumour. The histology was diagnostically challenging with notable presence of numerous perivascular pseudo-rosettes and negative immunoreactivity for all pituitary hormones. The differential diagnosis and importance of ancillary techniques is discussed.