Children born prematurely have a high incidence of visual disorders which cannot always be explained by focal retinal or brain lesions. The aim of this study was to test the hypothesis that visual function in preterm infants is related to the microstructural development of white matter in the optic radiations. We used diffusion tensor imaging (DTI) with probabilistic diffusion tractography to delineate the optic radiations at term equivalent age and compared the fractional anisotropy (FA) to a contemporaneous evaluation of visual function. Thirty-seven preterm infants (19 male) born at median (range) 28(+4) (24(+1)-32(+3)) weeks gestational age, were examined at a post-menstrual age of 42 (39(+6)-43) weeks. MRI and DTI were acquired on a 3 Tesla MR system with DTI obtained in 15 non-collinear directions with a b value of 750 s/mm(2). Tracts were generated from a seed mask placed in the white matter lateral to the lateral geniculate nucleus and mean FA values of these tracts were determined. Visual assessment was performed using a battery of nine items assessing different aspects of visual abilities. Ten infants had evidence of cerebral lesions on conventional MRI. Multiple regression analysis demonstrated that the visual assessment score was independently correlated with FA values, but not gestational age at birth, post-menstrual age at scan or the presence of lesions on conventional MRI. The occurrence of mild retinopathy of prematurity did not affect the FA measures or visual scores. We then performed a secondary analysis using tract-based spatial statistics to determine whether global brain white matter development was related to visual function and found that only FA in the optic radiations was correlated with visual assessment score. Our results suggest that in preterm infants at term equivalent age visual function is directly related to the development of white matter in the optic radiations.
Periventricular leucomalacia (PVL) and parenchymal venous infarction complicating germinal matrix/intraventricular haemorrhage have long been recognised as the two significant white matter diseases responsible for the majority of cases of cerebral palsy in survivors of preterm birth. However, more recent studies using magnetic resonance imaging to assess the preterm brain have documented two new appearances, adding to the spectrum of white matter disease of prematurity: punctate white matter lesions, and diffuse excessive high signal intensity (DEHSI). These appear to be more common than PVL but less significant in terms of their impact on individual neurodevelopment. They may, however, be associated with later cognitive and behavioural disorders known to be common following preterm birth. It remains unclear whether PVL, punctate lesions, and DEHSI represent a continuum of disorders occurring as a result of a similar injurious process to the developing white matter. This review discusses the role of MR imaging in investigating these three disorders in terms of aetiology, pathology, and outcome.
ABSTRACT:Our aim was to compare white matter (WM) microstructure in preterm infants with and without punctate WM lesions on MRI using tract-based spatial statistics (TBSS) and probabilistic tractography. We studied 23 preterm infants with punctate lesions, median GA at birth 30 (25-35) wk, and 23 GA-and sex-matched preterm controls. TBSS and tractography were performed to assess differences in fractional anisotropy (FA) between the two groups at term equivalent age. The impact of lesion load was assessed by performing linear regression analysis of the number of lesions on term MRI versus FA in the corticospinal tracts in the punctate lesions group. FA values were significantly lower in the posterior limb of the internal capsule, cerebral peduncles, decussation of the superior cerebellar peduncles, superior cerebellar peduncles, and pontine crossing tract in the punctate lesions group. There was a significant negative correlation between lesion load at term and FA in the corticospinal tracts (p ϭ 0.03, adjusted r 2 ϭ 0.467). In conclusion, punctate lesions are associated with altered microstructure in the WM fibers of the corticospinal tract at term equivalent age. (Pediatr Res 69: 561-566, 2011) M RI is increasingly being used to investigate brain development and pathology in infants who are born preterm. In addition to the major destructive white matter (WM) lesions, such as periventricular leukomalacia (PVL) and hemorrhagic periventricular infarction (HPI), that are observed on ultrasound, MRI studies have identified multiple punctate lesions in the WM in this group of infants. These lesions are observed as high signal intensity on T1-weighted imaging and low signal on T2-weighted imaging. Their distribution is widespread throughout the WM, and these lesions have been observed in the centrum semiovale (CSO), the corona radiata, the posterior periventricular WM (PPWM), the optic radiation, and, occasionally, in the frontal WM (1-4). They are quite common, being observed in 22% of infants in an unselected consecutive cohort and are more frequently observed in the preterm period than at term equivalent age (2).Diffusion tensor imaging (DTI) is an MRI technique that utilizes the Brownian motion of water in tissue (5). Within WM water diffuses preferentially along axons and is restricted perpendicular to axons (6). Quantitative measures derived from DTI, such as fractional anisotropy (FA), characterize the directional preference of diffusion and provide nonsubjective measures that reflect tissue microstructure (7). In diffusion tractography, it is assumed that the principal direction of diffusion in each imaging voxel is coincident with the underlying dominant fiber direction. Tractography generates 3D representations of WM tracts by following this principal diffusion direction on a voxel by voxel basis. DTI studies have previously demonstrated differences in WM microstructure between preterm infants and term controls (8 -11), and between preterm infants with diffuse or focal lesions and those with no evidence of a...
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