The pituitary gland, located at the base of the brain, is a small but critically important 'master gland' that controls hormonal systems throughout the body. Pituitary tumours in dogs are usually functional adenomas that secrete excess ACTH, leading to Cushing's disease (hyperadrenocorticism) — a condition characterised by increased drinking and urination, pot-bellied appearance, hair loss, and skin changes. When the tumour grows large enough (macroadenoma, typically >10 mm), it can press on surrounding brain structures, causing neurological signs such as lethargy, circling, or blindness. While the hormonal effects of Cushing's disease can be managed medically, the growing tumour mass itself requires different treatment — typically radiation therapy to shrink the tumour, or in specialised centres, surgical removal via the transsphenoidal approach.