A Morphometric Analysis of Cerebellar Vermis in Fetal Alcohol Spectrum Disorder

INTRODUCTION

An estimated 12% of all newborns (496,000 infants) in the United States have prenatal alcohol exposure. Maternal alcohol consumption during gestation can have significant effects on developing offspring resulting in anomalies in growth patterns, facial morphology, and alterations in neurocognitive processes. Studies suggest that the brain is most susceptible to prenatal alcohol exposure with effects in many regions identifiable through statistical analysis of segmented volumes or sectoral areas and their altered states (Goodlet et al., 1992; Roebuck et al., 1998; West et al., 1994).

Structural abnormalities have been reported using magnetic resonance imaging (MRI) based techniques. Several investigators have observed pronounced hypoplasia of the cerebellar vermis (Goodlet et al., 1990; Sowell et al., 1996; Riley et al., 2004). Notably, it has been reported through research using animal and human models that the anterior lobe (lobules I-V) of the vermis is most affected by the injurious effects of prenatal alcohol exposure (Goodlet et al., 1990; Sowell et al., 1996).

The morphometric effects of mild to heavy prenatal alcohol exposure on the cerebellar vermis in children without FAS continue to be poorly understood. These individuals generally are not diagnosed as having alcohol related disabilities because they have minimal to no growth retardation, normal facial features, and IQ scores in the average range. Importantly, children with varying degrees of alcohol exposure may have significant clinical and neuropsychological impairment resulting in a decreased ability for mental health disorders. (Malisza et al.,2005; Riley et al., 2003).

This paper will investigate the cerebellar vermal morphology in individuals with prenatal exposure. It was hypothesized that children with FAS and PEA would demonstrate volume reductions in the vermal regions compared with non exposed children.

METHODS

Subjects: The patient group consisted of 88 children and adolescents, between the ages of 6 and 16 years. All subjects underwent MRIs and were evaluated for the dysmorphic effects of prenatal alcohol exposure by a Dysmorphologist/Geneticist/PediatricNeurologist who was blind to the prenatal alcohol exposure status of the subjects. Based on clinical history and physical findings subjects were divided into four groups – FAS (n=17); prenatal exposure to alcohol (PEA) (n=21); ADHD without alcohol exposure (n=23); and no prenatal alcohol exposure or ADHD (n=27). Exclusion criteria for all children and adolescents in this study included serious closed head injury, epilepsy, major mental illness, including psychosis, Tourette's Disorder and or any of the pervasive developmental disorders.

Among the groups, the mean age for the FAS group was 11.6 years (S.D. 3.4) , PEA 12.3 years (S.D. 2.6 ), ADHD 10.9 years (S.D. 2.0) and Control 10.7 (S.D. 2.0). The majority of the children were male (57%) and Black (56%). All the individuals in the study were recruited from the Kennedy Krieger Institute Outpatient Programs and the surrounding community with IQ's ³ 65. Participants were excluded if the history of alcohol exposure couldn't be confirmed. All subjects had behavioral training available immediately before the MRI to help acquire the scan without the use of sedative-hypnotics. Informed consent was obtained from all children and their parents.

MRI MEASUREMENTS: All high-resolution coronal scans were acquired on a 1.5T Gyroscan NT Intera (Philips) scanner. The head was aligned with laser cross hairs referenced to the naison and the midsagittal plane. T1 weighted images were obtained with a Tr of 35 msec, a Te of 6 msec, and a flip angle of 45 degrees. The images used in this study were 1.5 mm thick. A field of view of 240 mm and a 256x256 matrix was used for this study as well.

Midline neuroanatomic structures were manually delineated using the program Brainimage (Reiss et al., 1997). A radiologist determined the guidelines for the operational definitions of regions of interest (Daniels et al., 1987). Area measurements of the corpus callosum, cerebellar vermis (lobules I-V, lobules VI-VII, and lobules VIII-X) and total intracranium was defined using the sagittal image that most clearly showed the cerebral aqueduct and the lobular anatomy of the cerebellar tonsil and hemisphere. Special consideration was taken to discern the cerebellar tonsil and hemispheres from the lobules of the vermis.

STATISTICAL ANALYSIS: Several different analyses were performed to evaluate the volumetric differences of the cerebellar vermis of the prenatally exposed alcohol subjects (PEA) in comparison with the FAS, ADHD and Control groups. The three cerebral volume measures were analyzed by mixed ANOVA, with Group as a between subjects factor (FAS vs. PEA vs. ADHD vs. Control), and Vermal region (anterior vermis, posterior vermis, total vermis) as the within-subjects variable. Linear regressions along with linear combination of estimates tests were used to further clarify any group differences (adjustments for age). In this study, midsagittal vermis measurements were compared with children divided into four groups. Statistical analyses were conducted comparing the total cerebellar vermis size, anterior cerebellar vermis size, and posterior cerebellar vermis size of the four groups.

RESULTS

The results of this study indicate that the volume of the total cerebellar vermis is disproportionately reduced in size in children with a diagnosis of FAS compared to groups of children with ADHD as well as matched controls (-2.30, 95% CI -1.10 to -3.60, p < 0.001 and -1.60, 95% CI – 0.40 to -2.80, p<.0.050, respectively). The anterior vermal region was found to be significantly reduced in the FAS group as compared to the PEA, ADHD, and control group (- 0.51, 95% CI – 0.06 to – 0.95, p < 0.026; -1.00, 95% CI – 0.61 to -1.50, p < 0.000 and – 0.96, 95% CI – 0.54 to -1.40, p < 0.000, respectively). The anterior vermis volume also showed a statistically significant difference between the PEA and control group (- 0.45, 95% CI – 0.06 to – 0.85, p < 0.026). No significant reductions were observed between groups in the posterior vermal region.

DISCUSSION

The overall results of this study demonstrate reductions in cerebellar vermis volumes in subjects with prenatal alcohol exposure whether the children had a confirmed diagnosis of FAS or alcohol exposure that did not lead to the typical growth and facial features of FAS. Unique to this study was that the PEA group had a range of alcohol exposure from minimal to heavy. In the majority of other studies of prenatal alcohol exposure that demonstrate statistically significant brain changes, the children with PEA have heavy prenatal alcohol exposure. Additionally, the control groups (ADHD and normal controls) used in this study were rigorously evaluated for any prenatal alcohol exposure.

This study suggests that there may be statistically significant group effects of any prenatal alcohol exposure on the overall cerebellar vermis volume of the prenatal exposure to alcohol group. These analyses replicate and extend the findings in previous studies that reveal a reduction in the anterior vermal lobules in children with FAS as compared to the PEA, ADHD, and Control groups (Goodlet et al., 1990; Sowell et al., 1996). Limitations of this preliminary study include almost a 20 point IQ differential between the FASD subjects and the ADHD and control subjects and differences in gender and race in the comparison groups.

Many morphometric studies to date have specifically focused on the examination of effects of high concentrations of alcohol on the cerebellar vermis of individuals with FAS or high rates of PEA who do not meet the criteria for FAS. However, our findings evaluated children with a wide range of alcohol exposures, not just heavy exposure. Thus, this preliminary study suggests that group effects of minimal to heavy prenatal alcohol exposure in the PEA group can have measurable neuroanatomical deficits on the developing brain.

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