Hypopituitarism

Neuroendocrine deficiencies are common delayed sequelae of cranial irradiation. While much of the data describe this side effect with standard fractionation radiation therapy, both single fraction and fractionated radiosurgeries (SRS and fSRS, respectively) can cause hypopituitarism. Factors that affect risk include total dose, fraction size, age at the time of radiation, and length of time after radiation therapy. Targets of radiation damage include both hypothalamic and pituitary cells. The mechanism is thought to be direct neuronal damage from ionizing radiation. A deficiency of one or more hypothalamic-pituitary hormones can develop depending on the radiation dose. Clinical syndromes from radiation-induced hypopituitarism include growth hormone (GH) deficiency, gonadotropin deficiency, precocious puberty, central adrenal insufficiency, thyroid-stimulating hormone (TSH) deficiency, and hyperprolactinemia. The GH axis is particularly sensitive and is frequently the only site affected by lower-dose radiation therapy. Screening for hypopituitarism and referral to appropriate specialists can avoid unnecessary morbidity in this patient population.