Lipid-containing cells in brains of normal and hypoxic infant monkeys: a quantitative and ultrastructural study

The significance of lipid-containing cells found at autopsy in the white matter of infant brains is controversial, particularly with respect to their postulated role as markers of the "sudden infant death syndrome." To determine whether such cells are indicative of prior nonlethal hypoxic insult, we quantitated them in the brains of control infant monkeys and in two groups of infant monkeys that were subjected to 30 minutes of hypoxic insult. One group consisting of monkeys that died less than 48 hours after the hypoxia, and the other of those that survived 7 to 13 days following the insult. The quantification of lipid-containing cells was undertaken in frozen brain sections stained with Oil red O; sections of brains from 4 perfusion-fixed animals were evaluated by electron microscopy. Lipid-containing cells were found in the corpus callosum, in the septum, and in periventricular white matter in both posthypoxic and control animals. There was a relationship between numbers of lipid-containing cells and the age of the animal; animals with large numbers were less than 28 days old. Decreases in numbers of lipid-containing cells correlated with advancing myelination as well as with age. Electron microscopic evaluation revealed lipid droplets in the cytoplasm of cells with irregularly shaped nuclei, densely clumped chromatin, occasional microtubules, and narrow cytoplasmic processes. We suggest that lipid-containing cells in the white matter of the brains of infants are related to age and to maturational factors and, in the absence of other pathologic signs, are not related to prior hypoxic injury.