Published online March 1, 2006
PEDIATRICS Vol. 117 No. 4 April 2006, pp. e619-e630 (doi:10.1542/peds.2005-0545)
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Reduced Fractional Anisotropy on Diffusion Tensor Magnetic Resonance Imaging After Hypoxic-Ischemic Encephalopathy

Phil Ward, BSca,b, Serena Counsell, PhDb, Joanna Allsop, DCR(R)b, Frances Cowan, PhDa, Yuji Shen, PhDb, David Edwards, Med Scia,b and Mary Rutherford, MD, FRCRb

a Department of Paediatrics, MRC Clinical Sciences Centre, Imperial College Faculty of Medicine, Hammersmith Hospital, London, England
b Imaging Sciences Department, MRC Clinical Sciences Centre, Imperial College Faculty of Medicine, Hammersmith Hospital, London, England

OBJECTIVE. Apparent diffusion coefficients (ADC) that are measured by diffusion-weighted imaging are reduced in severe white matter (WM) and in some severe basal ganglia and thalamic (BGT) injury in infants who present with hypoxic-ischemic encephalopathy (HIE). However, ADC values may pseudonormalize or even be high during this time in some less severe but clinically significant injuries. We hypothesized that fractional anisotropy (FA), a measure of the directional diffusivity of water made using diffusion tensor imaging, may be abnormal in these less severe injuries; therefore, the objective of this study was to use diffusion tensor imaging to measure ADC and FA in infants with moderate and severe hypoxic-ischemic brain injury.

METHODS. Twenty infants with HIE and 7 normal control infants were studied. All infants were born at >36 weeks' gestational age, and MRI scans were obtained within 3 weeks of delivery. Data were examined for normality, and comparisons were made using analysis of variance or Kruskal-Wallis as appropriate.

RESULTS. During the first week, FA values were decreased with both severe and moderate WM and BGT injury as assessed by conventional imaging, whereas ADC values were reduced only in severe WM injury and some severe BGT injury. Abnormal ADC values pseudonormalized during the second week, whereas FA values continued to decrease.

CONCLUSION. FA is reduced in moderate brain injury after HIE. A low FA may reflect a breakdown in WM organization. Moderate BGT injury may result in atrophy but not overt infarction; it is possible that delayed apoptosis is more marked than immediate necrosis, and this may account for normal early ADC values. The accompanying low FA within some severe and all moderate gray matter lesions, which is associated with significant later impairment, may help to confirm clinically significant abnormality in infants with normal ADC values.

Key Words: brain imaging • diffusion tensor imaging • hypoxic-ischemic encephalopathy • magnetic resonance imaging • neonates

Abbreviations: HIE—hypoxic-ischemic encephalopathy • GA—gestational age • DWI—diffusion-weighted imaging • ADC—apparent diffusion coefficient • WM—white matter • BGT—basal ganglia and thalami • ROI—region of interest • DTI—diffusion tensor imaging • FA—fractional anisotropy • RA—relative anisotropy • PLIC—posterior limb of the internal capsule • CSO—centrum semiovale • LN—lentiform nuclei • MT—medial thalamus • VLN—ventrolateral nuclei of the thalamus

Accepted Sep 23, 2005.


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