Hypopituitarism after cranial irradiation.

Radiation-induced damage to the hypothalamic-pituitary (h-p) axis is associated with a wide spectrum of subtle and frank abnormalities in anterior pituitary hormones secretion. While the rapidity of onset of these abnormalities is primarily radiation dose-dependent, their frequency and severity also depend on the length of follow-up. The GH axis is the most vulnerable to radiation damage, and GH deficiency is usually the only neuro-endocrine abnormality following irradiation of the h-p axis with doses <30 Gy. With higher radiation doses (30-50 Gy), the frequency of GH insufficiency can be as high as 50-100% and that of TSH and ACTH around 3-6%. Abnormalities in gonadotrophin secretion are dose-dependent; precocious puberty can occur after radiation dose <30 Gy in girls only, and in both sexes equally with a radiation dose of 30-50 Gy. Gonadotrophin deficiency occurs infrequently, and is usually a long-term complication following a minimum radiation dose of 30 Gy. Hyperprolactinemia has been described in both sexes and all ages, but is mostly seen in young women after intensive irradiation and is usually subclinical. A much higher incidence of gonadotrophin, ACTH and TSH deficiencies, (30-60% after 10 yr) occurs after more intensive irradiation (>70 Gy) used for nasopharyngeal carcinomas and tumors of the skull base, and following conventional irradiation (30-50 Gy) for pituitary tumors. Radiation-induced anterior pituitary hormone deficiencies are irreversible and progressive. Regular testing is mandatory to ensure timely diagnosis and early hormone replacement therapy, to improve linear growth and prevent short stature in children cured from cancer, to preserve sexual function, prevent ill health and osteoporosis, and improve the quality of life.