title: Hippocampal development at gestation weeks 23 to 36. An ultrasound study on preterm neonates.
abstract: BACKGROUND
  During fetal development, the hippocampal structures fold around the hippocampal sulcus into the temporal lobe. According to the literature, this inversion should be completed at gestation week (GW) 21. Thereafter, the hippocampal shape should resemble the adult shape. However, incomplete hippocampal inversion (IHI) is found in 19% of the common population. The aim of this study was to study fetal hippocampal development by examining neonates born preterm.
  
  
  METHODS
  We analyzed cranial ultrasound examinations, performed as a part of the routine assessment of all preterm infants, over a 3-year period and excluded the infants with brain pathology. The final material consisted of 158 children born <35 GW. A rounded form (the ratio between the horizontal and vertical diameters of the hippocampal body <or=1) in coronal slices was considered the sign of IHI.
  
  
  RESULTS
  The age at examination was 23-24 GW in 24 neonates, 25-28 GW in 70 neonates, and 29-36 GW in 64 neonates. IHI was found in 50%, 24%, and 14%, respectively. The difference between the neonates <25 GW and >or=25 GW was statistically highly significant (p < 0.001). The frequency of bilateral IHI was highest in the youngest age group. In the other groups, the left-sided IHI was the most common.
  
  
  CONCLUSIONS
  In about 50% of the neonates, hippocampal inversion is not completed up to GW 24; but from 25 GW onwards, the frequency and laterality of IHI is similar to that in the adult population.
authors.affiliation: Department of Radiology, University Hospital, Uppsala University, Uppsala, Sweden. dragan.bajic@akademiska.se
authors.forename: Dragan
authors.initials: D
authors.lastname: Bajic
authors.forename: Uwe
authors.initials: U
authors.lastname: Ewald
authors.forename: Raili
authors.initials: R
authors.lastname: Raininko
mesh_terms: D000328:Adult; D005260:Female; D006624:Hippocampus / Q000002:abnormalities* / Q000000981:diagnostic imaging* / Q000254:growth & development; D006801:Humans; D008297:Male; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D047928:Premature Birth / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014463:Ultrasonography