Aims Adults and children with Down syndrome (DS) have reduced total and regional brain volumes. No published studies describe brain volumes of neonates with DS. This study aims to analyse brain volumes in neonates with DS using a fully automatic brain tissue segmentation algorithm.
Methodology Neonates with DS and healthy term controls underwent MRI. Coronal T2 scans were acquired in a 1.5T scanner. Total brain tissue (TBT) was divided into cortical grey matter, white matter, deep nuclear grey matter, brainstem and cerebellum. TBT, in addition to ventricles and extra-axial cerebrospinal fluid, formed total intra-cranial volume (TICV). Two observers annotated all seven tissues types in three slices per scan. An automatic algorithm, using supervised learning was developed to segment all tissues in every slice. Thus, tissue types on each T2 scan were identified and volumes calculated.
Results Thirty neonates (20 DS, 10 controls) were recruited. Median birth gestation (weeks), birthweight (g) and head circumference (cm) in DS were 38+3, 3006 and 34.0, vs. Control infants 39+1 3340 and 34.9. The automated segmentations were compared with the observers’ annotations using Dice-coefficient (DC). The mean (SD) DC across tissues was 0.86 (0.06). Between the two observers this was 0.81 (0.06). Individual tissue volumes were calculated as a percentage of TICV (to adjust for head circumference). In DS infants, ventricular volumes as a percentage of TICV were significantly larger p = . 00001 and cerebellar volumes were significantly smaller p value. 03. TBT as a percentage of TICV was also significantly smaller in the DS group (p = 0.02). Results for all tissues are represented in Figure 1.
Conclusion This study has demonstrated that there are structural differences in the brain of Down syndrome infants, which are present at birth. In particular the ventricles are larger, the cerebellum is smaller and the total brain volume is smaller. This suggests that early brain development in DS is altered, and the differences observed in adulthood develop in utero as opposed to being the result of degeneration later in adult life.
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