Objective evaluation of sylvian fissure development by multiplanar 3-dimensional ultrasonography.

Evaluation of fetal cerebral cortex sulcation is important for the pre-natal diagnosis of neuronal migration disorders. Although abnormal sylvian fissure morphologic features are frequently observed in these conditions, the diagnosis of an abnormal sylvian fissure relies on subjective interpretation of ultrasonographic images. This study was performed to develop an objective ultrasonographic parameter for sylvian fissure evaluation. This cross-sectional study included 202 normal singleton pregnancies without fetal anomalies. Using multiplanar, 3-dimensional ultrasonography, the sylvian fissure midpoint was identified. The sylvian fissure-to-parietal bone distance (SPB) was measured from the midpoint to the inner surface of the parietal bone, perpendicular to the falx cerebri. Bland-Altman plots were used to determine intraobserver and interobserver agreement. Regression analysis was used to evaluate the correlation between SPB measurements and gestational age. Two hundred (99%) of 202 pregnancies had a visible sylvian fissure, identifiable as early as 12 weeks of gestation. The mean SPB values at 12 and 41 weeks were 2.1 and 14.3 mm, respectively. Intraobserver and interobserver mean differences between paired measurements were 0.01 mm (95% limits of agreement, -0.41 to 0.43 mm) and 0.05 mm (95% limits of agreement, -1.79 to 1.90 mm), respectively. A linear correlation was observed between the SPB and gestational age (multiple R=0.91; R2=0.82 [SPB = -2.85 + 0.42 x gestational age]). (1) The SPB can be reproducibly measured from 12 weeks of gestation to term; and (2) a strong positive correlation was observed between the SPB and gestational age.