The cavum septi pellucidi in term and preterm newborn infants.

We reviewed cranial sonographic studies done on 108 normal newborn infants to determine the prevalence and variability in size of the cavum septi pellucidi (CSP). Infants were classified according to gestational age by 2-week intervals. At 24 weeks, only four normal scans were identified. Between 26 and 34 weeks, ten consecutive normal scans were used since all infants had a CSP. At 36, 38, and 40 weeks, all normal scans were counted in order to obtain a prevalence estimate. A CSP was seen in all normal infants below 36 weeks of gestational age. At 36, 38, and 40 weeks, only 69%, 54%, and 36%, respectively, had CSPs. There was no significant change in the width, depth, or area of the CSP with age, birth weight, or biparietal diameter. A CSP greater than 0.95 cm in width or greater than 0.81 cm in depth is outside the normal range and may represent anomalous development of the midline structures of the brain.