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 red/purple object at upper centre, below and between the eyes, which are coloured gold with the lenses in purple. 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.