New MR imaging assessment tool to define brain abnormalities in very preterm infants at term

Abstract

Background and purpose: WM injury is the dominant form of injury in preterm infants. However, other cerebral structures, including the deep gray matter and the cerebellum, can also be affected by injury and/or impaired growth. Current MR imaging injury assessment scales are subjective and are challenging to apply. Thus, we developed a new assessment tool and applied it to MR imaging studies obtained from very preterm infants at term age.

Materials and methods: MR imaging scans from 97 very preterm infants (< 30 weeks' gestation) and 22 healthy term-born infants were evaluated retrospectively. The severity of brain injury (defined by signal abnormalities) and impaired brain growth (defined with biometrics) was scored in the WM, cortical gray matter, deep gray matter, and cerebellum. Perinatal variables for clinical risks were collected.

Results: In very preterm infants, brain injury was observed in the WM (n=23), deep GM (n=5), and cerebellum (n=23). Combining measures of injury and impaired growth showed moderate to severe abnormalities most commonly in the WM (n=38) and cerebellum (n=32) but still notable in the cortical gray matter (n=16) and deep gray matter (n=11). WM signal abnormalities were associated with a reduced deep gray matter area but not with cerebellar abnormality. Intraventricular and/or parenchymal hemorrhage was associated with cerebellar signal abnormality and volume reduction. Multiple clinical risk factors, including prolonged intubation, prolonged parenteral nutrition, postnatal corticosteroid use, and postnatal sepsis, were associated with increased global abnormality on MR imaging.

Conclusions: Very preterm infants demonstrate a high prevalence of injury and growth impairment in both the WM and gray matter. This MR imaging scoring system provides a more comprehensive and objective classification of the nature and extent of abnormalities than existing measures.

Fig 1.

Representative MR images of regional injury. Axial T1- or T2-weighted MR images demonstrating classification of cystic WM lesions (A–D), focal WM signal abnormalities (E–G), deep GM lesions (H and I), and cerebellar lesions (J and K). Cystic WM lesions are defined by their extent: focal unilateral (arrow, A), focal bilateral (arrows, B), extensive unilateral (C), and extensive bilateral (D). Focal WM signal abnormalities are classified as focal punctate (arrows, E), extensive punctate (arrows, F), or linear lesions corresponding to gliosis (arrows, G). Deep GM and cerebellar injuries are classified into 4 grades by their extent. Representative images of focal unilateral (arrow, H) or extensive unilateral (arrow, I) deep GM lesions, and images of focal bilateral (arrows, J) or focal extensive (arrow, K) cerebellar lesions are shown.

Fig 2.

Regional measurements. A, Biparietal width (BPW) and interhemispheric distance (IHD) are measured on a single coronal section by use of the cochlea and basilar truncus as landmarks. B, Callosal thickness is measured on a midsagittal view at 3 different regions: the genu, the midportion, and the splenium. C, Ventricular diameters (VDs) and transcerebellar diameter (TCD) are measured on a coronal view at the level of the ventricular atrium. D, The deep GM area (DGMA) is measured on a single axial section at the level at which the caudate heads, the lentiform nuclei, and the thalami are maximally visible.