Prenatal Exposure to Alcohol: What the Images Reveal.

Case studies and statistical analyses of groups of children with fetal alcohol syndrome (FAS) or prenatal exposure to alcohol (PEA) have been performed using magnetic resonance imaging (MRI) techniques. These studies show that alcohol exposure during pregnancy can result in a range of structural brain abnormalities. Among severely affected children, widespread damage may occur to the corpus callosum, basal ganglia, hippocampus, and cerebellum. Throughout the range of severity, however, overall reduction of the brain is apparent, and in particular, portions of the cerebellum, basal ganglia, and corpus callosum are disproportionately reduced in size among children with FAS and PEA. These children also have been shown to have cognitive deficits, although these have not been linked to abnormalities in specific brain areas. KEY WORDS: fetal alcohol syndrome; prenatal alcohol exposure; gestation; magnetic resonance imaging; brain damage; child; fetal alcohol effects The effects of exposure to alcohol during the prenatal period have been studied intensively using a variety of research methods, including autopsies, animal models, and imaging techniques. Through these efforts, investigators have learned that prenatal alcohol exposure1 can have devastating effects on the developing fetus and that these effects can be viewed as falling along a continuum. At the farthest end of the continuum are perinatal death and fetal alcohol syndrome (FAS) (see Jones and Smith 1973). An FAS diagnosis is made when an alcohol-exposed infant exhibits pre- or postnatal growth deficiency, a specific pattern of anomalies in the structure of the face and skull (i.e., craniofacial anomalies), and some central nervous system dysfunction (see figure 1). In addition to causing FAS, prenatal alcohol exposure can result in a variety of other severe effects, such as mental retardation and additional physical anomalies. But lesser cognitive deficits and behavioral difficulties related to prenatal alcohol exposure can be apparent even at the mild end of the continuum (see Jacobson and Jacobson 1994). For example, researchers have reported that exposure to even small amounts of alcohol (1-2 drinks per day) during prenatal development can lead to impaired attention (for review, see Streissguth 1986). The terms "fetal alcohol effects" (FAE) and "prenatal exposure to alcohol" (PEA) are sometimes used to describe people who do not exhibit all the features required for a diagnosis of FAS but for whom some physical or behavioral problems are ascribed to prenatal alcohol exposure. Although behavioral and developmental anomalies have been documented in children prenatally exposed to alcohol, no one has yet defined precisely what brain structures specifically are affected following such exposure. Researchers are beginning to apply imaging techniques--such as magnetic resonance imaging (MRI), which produces pictures of the brain's structure-- to investigate this question. MRI studies have shown that structures such as the cerebral cortex, cerebellum, basal ganglia, hippocampus, and corpus callosum appear to be affected by PEA. The cerebral cortex is the outer part of the brain and is necessary for a variety of higher cognitive functions; the cerebellum is found at the back of the brain and is involved in motor as well as cognitive activities; the basal ganglia are a group of structures that lie deep within the brain (under the cortex) and are involved in motor and cognitive skills. The hippocampus is involved in memory, and the corpus callosum is the tract of nerve fibers bridging the two brain hemispheres.2 This article reviews MRI findings that reveal a pattern of structural anomalies in the brains of children with FAS or PEA. Such research eventually may be linked to specific developmental and behavioral deficits observed in these children to clarify the nature of this disorder and discern the true capabilities of those who suffer from it. DOCUMENTING SEVERE BRAIN DAMAGE Autopsy Reports of Children With FAS The effects of prenatal alcohol exposure on the developing brain have received a great deal of attention since alcohol was first implicated in causing damage to the unborn fetus (i. …