Endocrine consequences of brain irradiation.

Cranial radiation is routinely used to manage pituitary tumours, craniopharyngiomas, primary brain tumours, tumours of the head and neck and, in the past, for the prophylaxis of intracranial disease in patients with acute lymphoblastic leukaemia. If the hypothalamic-pituitary axis falls within the radiation fields, the patient is at risk of developing hypopituitarism. The effect of radiation is determined by the dose and the time that has elapsed since treatment. Classically, growth hormone (GH) is the most sensitive of the anterior pituitary hormones to irradiation, followed by gonadotrophins, adrenocorticotrophic hormone (ACTH) and thyroid-stimulating hormone (TSH). Low-dose irradiation in prepubertal children can initially cause early or precocious puberty and subsequently gonadotrophin deficiency. Higher doses may cause gonadotrophin deficiency and pubertal delay. The ACTH and TSH axes are relatively resistant to the effects of irradiation, but minor abnormalities may occur. Patients who receive cranial irradiation that affects the hypothalamic-pituitary axis remain at risk of developing multiple hormone deficiencies for many years and require long-term follow-up by an endocrinologist.