Megalencephaly in sudden infant death syndrome.

The fresh brain weights of 79 infants with sudden infant death syndrome (SIDS) were tabulated and compared with expected "normal" brain weights. The series included 47 males and 32 females. Their ages ranged from 8 days to 16 months with a median of 2.5 months. The weights of all these brains were above the 50th percentile for age, and 64 of 79 brains (81%) were above the 95th percentile, including 15 (19%) at or above the 99.9th percentile. The ratio of the brain stem plus cerebellum weight to the whole brain weight of 93 formalin-fixed brains from victims of SIDS showed that the cerebrum was disproportionately heavier in most cases. No gross or microscopic evidence of cerebral edema was noted to account for the heavier weight. The significance of these findings is debatable. The increase in brain weight was less obvious in infants younger than 1 month of age but accelerated after that age. The brain weights of infants with SIDS may represent the really "normal" weights, since these patients were not known to be ill prior to death. If the brain weights of SIDS infants are really heavier than "normal," the possibility must be considered that disproportionately rapid growth of the brain during early infancy may be detrimental to the neural control of the cardiorespiratory system.