MRI and Prenatal Alcohol Exposure: Images Provide Insight Into FAS.

Twenty years have passed since the damaging effects of heavy prenatal alcohol exposure(1) on children were first noted in the United States (Jones et al. 1973). A consistent pattern of facial malformations, growth retardation, and varying degrees of central nervous system dysfunction became known as fetal alcohol syndrome (FAS). During an autopsy, the brain of an infant who died at 5 days of age was found to be extremely abnormal (Jones and Smith 1975). The infant, whose condition was one of the first to be diagnosed as FAS, had a small brain that was missing the corpus callosum (see figure 1 for a description and diagram of this and other brain areas), a structure that allows information to be transmitted between the two brain hemispheres.(figure 1 omitted) During normal embryological development, the nerve cells and the cells that give them structural support migrate to their appropriate positions in the brain. In this infant, the autopsy showed that throughout the brain tissue, there were cells, which could be differentiated by appearance, that had settled in inappropriate places. Other reports of brain anomalies in children with FAS include increased fluid in the brain, or hydrocephalus; abnormalities of specific areas of the brain, such as the corpus callosum and cerebellum; and evidence of disorganized cell migration during development (Clarren 1986). Some of these findings have been supported by research that uses animal models of prenatal alcohol exposure. Rats and mice exposed to alcohol before birth have been shown to have numerous abnormalities in the brain, including an abnormally small head (microcephaly); altered migration of brain cells, or neurons; and abnormalities of the cerebellum (Miller 1993; West and Pierce 1986). The cerebellum is the structure responsible for coordination of movement and posture and is also believed to have a role in some aspects of cognition. MAGNETIC RESONANCE IMAGING Recently, new technology has allowed researchers to use a noninvasive technique to look at brains of living children. Magnetic resonance imaging (MRI) produces x-raylike pictures of the brain without using radiation. MRI works like this: a large magnet causes the atoms in the brain to line up in a consistent fashion. An electromagnetic signal then passes through the magnetic field and provides energy that is absorbed by the aligned atoms. When the electromagnetic signal is discontinued, the atoms release measurable amounts of energy. Different tissues in the brain, such as gray matter and white matter, that have different chemical compositions absorb, and thus release, energy in different ways. For example, the corpus callosum, which is primarily white matter, is distinguishable on an MRI from the cerebellum, which is mainly gray matter. These energy signals are converted to pictures of the brain (Jernigan 1990). Magnetic resonance images can appear as three-dimensional pictures or can be divided into two-dimensional "slices" of specific areas of interest. This article addresses the use of MRI in ongoing research on brain structure and function in FAS. RESEARCH FINDINGS In continuing research. we have conducted MRI evaluations on 12 children whose mothers were known to consume large amounts of alcohol while pregnant; 4 of the children have been subjected to detailed quantitative evaluations. In these four children, the volumes of particular brain areas were determined for comparison with the volumes of these areas in normal, healthy children. Two of these cases were adolescents with a clinical diagnosis of FAS (Mattson et al. 1992). The other two cases were adolescents with a known history of heavy in utero alcohol exposure but who lacked sufficient characteristics to warrant the clinical diagnosis of FAS (Mattson et al. in press a). These two cases are referred to as "PEA." for prenatal exposure to alcohol. MRI evaluations revealed that all four children were microcephalic. …