Sella rule 6 :Hypodense or hypointense pituitary lesion less than 1 cm in diameter.

A lesion less than 1 cm noted in the pituitary gland as a hypo dense mass in contrast CT examination or as a hypo intense mass in contrast conventional or dynamic MRI is considered to be a pituitary adenoma until prove otherwise.

Its differential diagnosis is a pituitary cyst or artifact.