Cerebral volume at term age: comparison between preterm and term-born infants using cranial ultrasound.

BACKGROUND AND AIMS

Very preterm infants are at particular risk of neurodevelopmental impairments. This risk can be anticipated when major lesions are seen on cerebral ultrasound (cUS). However, most preterm infants do not have such lesions yet many have a relatively poor outcome. Our study aims were to describe a tri-dimensional cUS model for measuring cranial and brain volume and to determine the range of brain volumes found in preterm infants without major cUS lesions at term equivalent age (TEA) compared to term-born control infants. We also aimed to evaluate whether gestational age (GA) at birth or being small for gestational age (SGA) influenced estimated brain size.

METHODS

We scanned a cohort of very preterm infants at TEA and term-born controls. Infants with major cerebral lesions were excluded. Measurements of intracranial diameters (bi-parietal, longitudinal, cranial height), brain structures, ventricles and extracerebral space (ECS) were made. A mathematical model was built to estimate from the cUS measurements the axial area and volumes of the cranium and brain. Appropriate statistical methods were used for comparisons; a p-value under 0.05 was considered significant. SGA infants from both groups were analysed separately.

RESULTS

We assessed 128 infants (72 preterms and 56 controls). The preterms' head was longer (11.5 vs. 10.5 cm, p < 0.001), narrower (7.8 vs. 8.4 cm, p < 0.001) and taller (8.9 vs. 8.6 cm, p < 0.01) than the controls'. Estimated intracranial volume was not statistically different between the groups (411 vs. 399 cm(3), NS), but preterms had larger estimated ECS volume (70 vs. 22 cm(3), p < 0.001), lateral ventricular coronal areas (33 vs. 12 mm(2), p < 0.001) and thalamo-occipital distances (20 vs. 16 mm, p < 0.001), but smaller estimated cerebral volume (340 vs. 377 cm(3), p < 0.001). Smaller brain volumes were associated with being of lower gestational age and birth weight and being small-for-gestational age.

CONCLUSIONS

We have developed a model using cranial ultrasound for measuring cranial and brain volumes. Using this model our data suggest that even in the absence of major cerebral lesions, the average extrauterine cerebral growth of very preterm infants is compromised. Our model can help in identifying those preterm infants with smaller brains. Later follow-up data will determine the neurodevelopmental outcome of these preterm infants in relation to their estimated brain volumes.