Abstracts

Rationale: Measuring the volume of specific brain areas in studies of paediatric subjects often requires correction for intracranial volume (ICV). This is of particular importance when conducting follow-up and longitudinal studies, and may be of use in clinical practice. However, measuring ICV can be labour intensive and time consuming. Intracranial area (ICA) has been used to predict total ICV in adults (Ferguson et al, 2005), but not in the developing brain. ICA is faster than measuring the total ICV and does not require extensive automated processing. ICA may, therefore, provide a useful alternative to measuring ICV for research studies and in clinical practice. The aim of this study was to investigate whether ICA predicts total ICV in a healthy paediatric cohort, and in children with convulsive status epilepticus (CSE). Methods: T1-weighted volumetric MRI was performed on 20 healthy children, 9 with CSE with qualitatively assessed, structurally normal MRI, and 10 with CSE with structurally abnormal MRI. ICA was measured on a midline sagittal slice and was compared against ICV measurements. Informed consent was taken from all parents of children involved and the study was approved by the Great Ormond Street Hospital (GOSH) research ethics committee. Results: ICA measurements were highly reliable, with intra- and inter-rater correlations of 1.0 (p<0.0167 and p<0.0001, respectively). In the group of healthy subjects a high Spearman correlation was found between the ICA and ICV measurements (r=0.96; p<0.0001). A high Spearman correlation was found between ICV and ICA in the structurally normal (r=0.9; p<0.002, n=9) as well as abnormal (r=0.9; p<0.0008; n=10) groups. However, significant differences were found in corrected ICV between controls and the group of children with abnormal scans (ANOVA, p<0.001) with those children having relatively smaller ICV for a given ICA than controls. Distance from predicted values was greater for those children with structural abnormalities affecting more than one lobe of the brain than those with more localized lesions (Mann-Whitney U, p=0.033).Conclusions: ICA measurement can be a useful alternative to measuring ICV in children, when correcting volume measurements for brain size. Care needs to be taken in those with qualitatively determined significant brain pathology, however, the method may remain valid for those with only localized pathology. Reference: Ferguson KJ, Wardlaw JM, Edmond CL, Deary IJ, Maclullich AMJ. (2005). Intracranial area: a validated method for estimating intracranial volume. J neuroimaging. 15(1), p76 8.