Pituitary tumour: false-colour magnetic resonance image (MRI) of an axial section of the brain showing a large pituitary adenoma, a type of tumour. The pituitary adenoma appears as the bright green object at upper centre, below and between the eyes, which are coloured blue with the lenses in red. The pituitary is the master endocrine gland, secreting a number of hormones. Pituitary tumours are rare, comprising about 10% of primary brain tumours, and most are benign. Their effects are produced through changes in hormone secretion (increasing or decreasing) & local pressure effects - on the optic nerves, for example.