Sonographic maturation of third-trimester cerebellar foliation after birth.

The development of cerebellar folia of third-trimester preterms has not been described with ultrasound before. We set out to determine normal development of the pons and cerebellar folia for future measurements of hypoplasia and atrophy. Study sonograms were made in preterms admitted to the neonatal intensive care unit with postmenstrual age (PMA) from 25 wk until term. On a weekly basis, transcranial measurements were made in the axial and coronal planes at the asterion with high-frequency transducers (8.5 and 13 MHz). The axial images showed the pons and fourth ventricle. The coronal images showed cerebellar folia and white matter. In the same coronal plane, the depth of cerebellar fissures at the rostral cerebellar convexity could be observed. A total of 172 cranial sonograms were performed on 98 neonates. The development of folia could be measured with ultrasound through the asterion. We showed that pons area, mean of three fissure depths, hemisphere area, and number of folia in the horizontal fissure correlated significantly with PMA. Hemisphere area described the same trend of growth as the transverse cerebellar diameter used in fetal sonography.