The fetal vermis, pons and brainstem: normal longitudinal development as shown by dedicated neurosonography

To describe the normal appearance and the growth of the fetal vermis, pons and midline brainstem by ultrasound from 18 weeks of gestation to term in order to produce developmental nomograms.

Serial ultrasound examinations of the fetal brain were performed in 21 fetuses between 18 and 39 weeks of gestation every two weeks. A total of 173 examinations were done, 8.2 ± 5.2 examinations per fetus. A mid-sagittal plain of the brain was obtained either by transvaginal or transabdominal sonography. Antero-posterior, cranio-caudal diameters, and surface area of the pons and the vermis were measured. The surface area of the brain stem was also measured. Nomograms were produced according to Royston and Wright.

The pons, vermis and brain stem grow in a linear fashion throughout pregnancy. The growth pattern correlates well with gestational age, biparietal diameter, head circumference and the cerebellar transverse diameter.

We have provided nomograms for assessment of the fetal brainstem. The present information supplies tools for the accurate identification of fetal mid-hindbrain anomalies providing a solid basis for a multidisciplinary approach, management and counseling of these conditions.