Assessment of fetal Sylvian fissure operculization between 22 and 32 weeks: a subjective approach

Sylvian fissure operculization (SFO) is a dynamic process throughout gestation and is a reliable feature of fetal cortex gyration that is amenable to prenatal ultrasound examination. This study aimed to define a subjective and reproducible method for SFO assessment.

This was a cross-sectional study of the sonographic anatomy of SFO conducted over a 9-month period in 200 fetuses with normal anatomical ultrasound examination at 22-32 weeks of gestation. We used a standardized view in an axial cerebral plane. SFO was scored according to a pre-defined scoring sheet based on the degree of overriding of the insula by the temporal lobe across gestational age. Because of the nested nature of the dataset, linear mixed effects models were used for concurrent assessment of inter- and intraobserver agreement of this scoring method. Subject-specific variance of the score was derived for each week of gestation from the whole repeated-measures dataset and the 5(th) and 95(th) percentiles of the score (mean score(week) +/- 1.645 SD(subject, week)) were determined.

The inter- and intraobserver agreement correlation coefficients were 0.91 (0.89-1.00) and 0.95 (0.93-1.00), respectively, with a standard error of measurement < 1 scoring unit, which corresponds to an accuracy of within 1 week. A reference chart was fitted, showing the increase of the SFO score between 22 and 32 weeks, along with age-specific 5(th) and 95(th) percentiles.

A simple scoring evaluation of the SFO is a reliable method for its assessment at between 22 and 32 weeks of gestation.