Prenatal radiation risk to the brain.

The Central Nervous System (CNS) exhibits a high sensitivity to ionizing radiation from conception until after birth. X-irradiation damage of the nervous system during development has been well documented and exposure to ionizing radiation above approximately 10 cGy during perinatal development is contraindicated. Shielding of the embryo or fetus usually prevents gross malformations but high energy irradiation of the pregnant female may result in embryonic growth retardation. This may be especially true when the irradiation is coupled with an ethanol-induced reduction in SOD activity. The synergistic interactions between other drugs and ionizing radiation also have been demonstrated. However, the concentration of endogenous compounds such as histamine and serotonin may be increased in the maternal circulation following irradiation and reach the fetal CNS through a blood-brain-barrier that is more permiable than normal. The introduction of histamine and/or serotonin into the fetal circulation may result in fetal hypotension, edema, cerebral ischemia, and damage to the developing CNS.