Normal cavum veli interpositi at 14–17 gestational weeks: three‐dimensional and Doppler transvaginal neurosonographic study

ABSTRACT Objectives To provide evidence to support the hypothesis that the midline cyst‐like fluid collection that is frequently observed on fetal brain ultrasound (US) imaging during the early second trimester represents a normal transient cavum veli interpositi (CVI). Methods This was a retrospective analysis of 89 three‐dimensional normal fetal brain volumes, acquired by transvaginal US imaging in 87 pregnant women between 14 and 17 gestational weeks. The midsagittal view was studied using multiplanar imaging, and the maximum length of the fluid collection located over (dorsal to) the tela choroidea of the third ventricle was measured. We calculated the correlation of the transverse cerebellar diameter (TCD) and of the maximum length of the fluid collection with gestational age according to last menstrual period. Color Doppler images were analyzed to determine the location of the internal cerebral veins with respect to the location of the fluid collection. Reports of the second‐trimester anatomy scan at 22–24 weeks were also reviewed. Results Interhemispheric fluid collections of various sizes were found in 55% (49/89) of the volumes (mean length, 5 (range, 3.0–7.8) mm). There was a strong correlation between TCD and gestational age (Pearson's correlation, 0.862; P