The subarachnoid space: normal fetal development as demonstrated by transvaginal ultrasound.

Enlargement of the subarachnoid spaces can be seen in the following conditions: communicating hydrocephalus, brain atrophy and benign enlargement of the subarachnoid spaces. These disorders may begin in utero. There are no established normograms for the fetal subarachnoid spaces. This study was conducted in order to determine its normal development. Transvaginal sonography was used to examine the subarachnoid space in 80 fetuses between 16 and 40 weeks' gestation. The sinocortical width (SCW) and craniocortical width (CCW) were measured in a coronal plane at the level of the foramen of Monro. The SCW remained relatively constant during the gestational period. The CCW increased in size from the 20th to the 28th week of pregnancy, with a subsequent gradual decrease until term. Determination of fetal subarachnoid space normograms may potentially help in the diagnosis of pathological conditions affecting this space and allow prenatal counselling.