Pituitary apoplexy is an acute clinical syndrome caused by either haemorrhage or infarction of the pituitary gland. It typically comprises of headache, visual deficits, ophthalmoplegia, and altered mental status. An existing pituitary macroadenoma is usually present (60-90%) but it can occur with healthy glands in few isolated cases. MRI typically demonstrates a pituitary region mass. T1: hyperintense due to blood (see ageing blood on MRI) http://radiopaedia.org/articles/pituitary-apoplexy
Pituitary macrocadenomas are the most common suprasellar mass in adults, and responsible for the majority of transsphenoidal hypophysectomies. They are defined a as pituitary adenomas greater than 10 mm in size. MRI is the preferred imaging modality, not only able to exquisitely delineate the mass, but also clearly visualise the optic chiasm, anterior cerebral vessels and cavernous sinuses. http://radiopaedia.org/articles/pituitary-macroadenoma-1
The infundibulum sign is helpful in distinguishing an empty pituitary sella from a cystic lesion of the pituitary region. In the former, although the sella is enlarged, there is no mass as such and the pituitary infundibulum traverses the enlarged sella to its floor where residual pituitary tissue is present. http://radiopaedia.org/play/158/case/24490/discussion