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Late Effects




Hypothalamic-Pituitary Axis

The hypothalamic-pituitary axis is the interface between the nervous and the endocrine system.

The hypothalamus has extensive neural connections with with other regions of the brain and regulates many functions such as appetite control.

The hypothalamus contains two types of neurosecretory cells:

1. Neurohypophysial neurons

  • Release vasopressin and oxytocin from nerve endings in posterior pituitary
  • Traverse hypothalamic-pituitary stalk

2. Hypophysiotropic neurons


The hypothalamic-pituitary axis is very vulnerable to damage from:

  • Tumor growth/pressure effects
    • Craniopharyngioma
    • Hypothalamic/chiasmatic tumor
    • Hydrocephalus and raised pressure in thrd ventricle
  • Surgical trauma
  • Radiation therapy (RT)
  • Chemotherapy


Radiation therapy and the hypothalamus:

  • There is evidence that the hypothalamus is more sensitive to RT than the pituitary
  • After lower doses of RT (used for TBI and low dose prophylactic cranial RT) the primary site of damage is the hypothalamus (usually associated with isolated GH deficiency)
  • Higher doses of RT (used for treatment of brain tumors) produce damage to the anterior pituitary with multiple pituitary hormone deficiencies
  • The incidence of hypothalamic-pituitary deficiency after RT is time dependent
  • The longer the time from RT, the higher the incidence of hormonal deficits



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