The normal 14–18 gestational weeks “parasagittal complex” view of the fetal brain. A 3D transvaginal neurosonographic study

Objective: To study the early second trimester development of brain hemispheres, lateral ventricles, choroid plexus, and ganglionic eminence/basal ganglia complex (GEBG). Methods: A retrospective analysis of TVUS 3D volumes of 14–18 gestational weeks (GW) fetuses. Hemispheres were analyzed for wall thickness, choroid plexus extension, GEBG height and length, lamination pattern (intermediate zone and the subplate border, IZ-SP), ventricle height, width, and angle. Measurements were correlated with GW and assessed for symmetry and impact of probe resolution. Results: We included 84 fetuses (168 hemispheres). The CP location is variable at 14–16 GW, becoming consistently and symmetrically posterior at 18 GW. Hemispheric thickness, GEBG height and length grow significantly with fetal age, whereas ventricle height, width, and angle regress. The detection rate of the IZ-SP line at 14, 15, 16, 17, and 18 weeks was 0%, 24%, 78.26%, 100%, and 100%, respectively. The ratio between the upper and lower segments of the cerebral lamination grows with GW. For all brain structures, the asymmetry between sides was significant only for ventricular height. The transducer type did not have a significant effect on any outcome except for ventricle height. Conclusion: These normal features of the parasagittal view should aid clinicians in fetal brain assessment during the early weeks of the second trimester.