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NEONATAL SOCIETY ABSTRACTS

Morphological differences of neonatal cerebral vascular development associated with preterm delivery: an MRA study at 3 tesla

Presented at the Neonatal Society 2004 Autumn Meeting (programme).

Malamateniou C1, Counsell SJ1, Allsop JM1, Fitzpatrick JA1, Boardman JP2, Srinivasan L2, Schmitz SA1, Cowan FM2, Hajnal JV1, Rutherford MA1

1 Imaging Sciences Department, Hammersmith Hospital, Imperial College London, UK
2 Department of Paediatrics, Imperial College London, UK

Background: Recent studies have highlighted differences in brain development in preterm infants at term equivalent age when compared to term born infants (1). These occur in the absence of focal pathology. The third trimester of fetal development is a period of excessive growth and very high metabolic demands. About 70% of the energy is used on brain and vessel development. To our knowledge no other previous qualitative or quantitative systematic studies of the morphology and patterning of neonatal cerebral macrocirculation have been carried out so far.

Aims: The aim of the study is to identify whether the neonatal cerebral macrocirculation develops differently in- and ex utero and to test the null hypothesis that there is no difference in the morphology and patterning of the major cerebral arteries of neonatal brain between term infants and preterm infants imaged at term equivalent age.

Methods: The study group consisted of 20 infants, 10 term scanned for different clinical reasons and 10 preterm imaged at term equivalent age. The study was approved by the Hammersmith Hospitals Trust Ethics Committee and informed consent was obtained for all of these infants. Infants were scanned on a 3 Tesla Philips Intera scanner with either a T/R or a SENSE head coil. Time of Flight Magnetic Resonance Angiography images were obtained with the following imaging parameters of an optimized dedicated for neonatal cerebral vasculature protocol: TR:18ms, TE:8.1ms, Flip Angle:16 deg, slice thickness: 0.6mm, FOV:160, 288x288 matrix (2). Vascular tortuosity was quantified in 10 infants, 5 preterm and 5 term, using the 1.32 version of ImageJ medical image software and tortuosity indices were calculated in the transverse plane for both the middle cerebral arteries (MCAs) of each infant. There was no significant difference in the age at scan of the two groups (41.2 the median for both groups). 3D cine image rotation was used to confirm anatomic segmentation and all images were acquired with the same anatomic coverage and angulation of the acquisition slab, otherwise new rotated Maximum Intensity Projections (MIPs) were generated as appropriate. Data were tested for normality and compared using a paired t test.

Results: Visual analysis of the two dimensional MIP Angiography Images revealed a characteristic pattern of decreased tortuosity of the vasculature of preterm infants(fig.1) imaged at term equivalent age in comparison to their term born counterparts (fig.2), that was more evident in the transverse MIPs and the middle cerebral artery. Quantitative measurements showed that tortuosity in both the right and left MCAs was significantly increased in the term infants with p=0.0074 and p=0.003 respectively.

Acknowledgements: The authors would like to thank the Greek State Scholarship Foundation (IKY), the MRC, the Academy of Medical Sciences, the Health Foundation and Philips Medical Systems for support.

Discussion: Premature delivery appears to have a marked effect in the development of cerebral vessels. We have shown that preterm infants have a distinct phenotype of less tortuous vessels. We need to measure tortuosity in a larger group of infants looking at the effect of postnatal age, body weight, brain volume, as well as vessel diameter and density. Several differences in the ex utero environment may be responsible for this morphological difference of the vessels in preterm infants These include a deficiency of essential fatty acids, mainly DHA (Docosahexaenoic Acid) and AA (Arachidonic Acid), which are known to cross the placenta in large amounts during the third trimester and play a cardinal role in the development of the brain and its vessels (3). In addition the preterm infant is relatively hyperoxic compared with the fetus, which may switch off the off the normal vasogenic / angiogenic factors.

References
1.Counsell SJ Pediatrics 2003; 112 (1 Pt 1):1-7
2.Malamateniou C Proceedings BCISMRM 2004
3.Crawford MA Am J Clin Nutr 1997; 66(4): 1032S-1041S

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