Specific Imaging Findings

Macroadenomas are frequently of heterogeneous appearance, reflecting cystic, necrotic, or hemorrhagic portions of the neoplasm. Contrast enhancement of the tumors is usually not prominent; the post-contrast images are used to visualize the normal avidly enhancing pituitary tissue. The location of the bright posterior lobe should be established on precontrast T1WI, to minimize chances of permanent postoperative diabetes insipidus. The frequent suprasellar tumor spread leads to the characteristic “figure of 8” or “snowman” appearance. The relationship with the optic chiasm is best evaluated on coronal T2WI, since the chiasm (composed of white matter tracts) is clearly hypointense. Cavernous sinus invasion is assessed on coronal images using virtual intercarotid lines that connect the cavernous and supracavernous ICA segments. Signs of cavernous sinus invasion are: tumor surrounding more than 66% of the cavernous ICA circumference, crossing the lateral intercarotid line, and extending into the medial venous compartment (the portion of the cavernous sinus immediately inferior to the ICA). DWI may show high signal intensity in infarcts and acute hemorrhages of acute pituitary apoplexy. Modern CT scanners can be effectively used when MR imaging is contraindicated.

Pertinent Clinical Information

Pituitary adenomas are more commonly diagnosed in women than in men and nonspecific symptoms, such as headache, are common. By convention 10 mm is used as the size threshold to separate macroadenomas from microadenomas. Non-functional pituitary adenomas present with symptoms associated with compression on the adjacent structures, most notably bitemporal hemianopsia, and are usually diagnosed late when they have reached macroadenoma size.