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Relationship between white matter apparent diffusion coefficients in preterm infants at term equivalent age and developmental outcome at two years

Presented at the Neonatal Society 2007 Summer Meeting (programme).

Krishnan ML1, Dyet LE1, Boardman JP1, Kapellou O1,2, Allsop JM1, Cowan F2, Edwards AD1,2, Rutherford MA1,2, Counsell SJ1

1 Robert Steiner MR Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Imperial College London, Hammersmith Campus, DuCane Road, London, W12 0HS, UK
2 Department of Paediatrics, Imaging Sciences Department, MRC Clinical Sciences Centre, Imperial College London, Hammersmith Campus, DuCane Road, London, W12 0HS, UK

Background: Diffusion weighted imaging (DWI) provides a measure of the Brownian motion of water particles, expressed as the apparent diffusion coefficient (ADC). ADC values have been shown to be higher at term equivalent age in preterm infants with diffuse excessive high signal intensity (DEHSI) in white matter (WM). In addition, ADC values in DEHSI were not significantly different from those in the WM of infants with focal WM injury (1). Elevated ADC values are associated with a decrease in volume of central grey matter in preterm infants with no signs of acute injury, suggesting a failure of growth and abnormal connectivity of these structures (1).

Objective: To develop a simple reproducible method for the measurement of ADC values in the white matter of preterm infants at term equivalent age using DWI, in order to test the hypothesis that elevated mean ADC values are associated with lower developmental quotient (DQ) scores at 2 years corrected age.

Subjects: Ethical permission was granted by the Hammersmith Hospital Research Ethics Committee, and written informed parental consent was obtained for each infant. We obtained DWI at term equivalent age in 38 preterm infants who had no evidence of overt cerebral pathology on conventional magnetic resonance imaging.

Methods: Mean WM ADC values at the level of the centrum semiovale were determined. At 2 years corrected age a neurological optimality score was determined (3) and the DQ obtained using the Griffiths Development Scales. The relationship between mean ADC values and DQ was examined using linear regression analysis. Clinical data relating to post-natal sepsis, antenatal steroid exposure, supplemental oxygen, gender, patent ductus arteriosus and inotrope requirement were collected. Unpaired t-tests were used to assess whether the mean ADC values were significantly different between clinical groups.

Results: The mean (±sd) ADC value in the WM was 1.385 ± 0.07 x 10-3mm2/s and the mean DQ was 108.9±11.5. No child had evidence of cerebral palsy at 2 years and the median neurological optimality score was 75 (range 69-78, optimal range 73-78). There was a significant negative correlation between mean ADC and DQ (p=0.014). ADC values were significantly elevated in infants with a history of postnatal sepsis (p=0.03).

Conclusion: These findings suggest that higher white matter ADC values at term equivalent age in preterm infants without overt lesions are associated with poorer developmental performance in early childhood. Consequently ADC values at term may be of prognostic value for neurodevelopmental outcome in infants born prematurely and who have no other imaging indicators of abnormality.

1 Counsell SJ, et al. Pediatr 2003;112:1-7.
2 Boardman JP, et al. Neuroimage 2006;32:70-80.
3 Haataja L, et al. J.Pediatr. 135, 153-161.

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