The majority of pituitary tumours are benign adenomas.The tumours may be hormonally active and become manifest as clinically identifiable syndromes associated with the excessive hormone production.Inactive small adenomas do usually not cause symptoms and often are incidental findings.Large macroadenomas may cause symptoms not related to the hormone production by local compression (especially visual field defects and/or impairment of vision) or they may block the normal hormone production.