VULNERABILITY OF THE INFANT BRAIN-STEM TO ISCHEMIA - A POSSIBLE CAUSEOF SUDDEN-INFANT-DEATH-SYNDROME

In infants, extreme extension or rotation of the head can occlude one or both vertebral arteries. We sought to determine whether small commu nicating arteries or asymmetric vertebral arteries could predispose th e brain stem to ischemia should such head movements occur. In 68 infan ts, the carotid, posterior communicating, precommunicator posterior ce rebral, basilar and vertebral arteries were fixed in formalin, embedde d in resin, the circumferences measured by image analysis, and the rel ative conductance of blood in each artery per gram of brain calculated . Conductance in the vertebrobasilar and carotid systems lagged behind increases in brain weight during the postnatal growth spurt. In 81% o f infants, conductance through the communicating arteries was less tha n 25% of basilar artery conductance. Conductance in one vertebral arte ry was less than half that of the contralateral artery in 41% of infan ts. In conclusion, the lag in available blood flow and small communica ting and asymmetric vertebral arteries may predispose the infant brain stem to ischemia if one or both vertebral arteries are occluded by he ad rotation or extension. Because these head movements are likely to b e accentuated in the prone sleeping position (a risk factor for sudden infant death syndrome), we suggest that vertebral artery occlusion ma y underlie some cases of sudden unexpected infant death.