Diagnosis of fetal cortical abnormalities by new reference charts for assessment of sylvian fissure biometry

Abstract

Objective To develop novel fetal reference ranges for the characterization of the normal appearance of the Sylvian fissures (SF) along gestation and to apply them to fetuses with cortical abnormalities affecting the SF. Methods In this cross‐sectional study, we used three‐dimensional sonographic multiplanar reformatting (3D‐MPR) to examine the fetal SF. Normal development was assessed in the second and third trimesters. SF parameters were evaluated in predefined axial and coronal planes: insular height and length, SF depth, and the extent of the coverage of the insula by the frontal and temporal lobes. Intra‐observer variability and inter‐rater reliability for the studied parameters were evaluated. The new reference charts were applied to 19 fetuses with cortical abnormalities involving the SF who had appropriate sonographic volumes for 3D‐MPR analysis. Their diagnoses were confirmed by autopsy, fetal or postnatal MRI, genetic findings related to cortical malformations, or an abnormal cortical imaging pattern with similar MRI findings in an affected sibling. We applied the two previously published references for the evaluation of fetal SF development to these cases and compared the ability of the references to correctly detect SF abnormalities. Results The study included 189 fetuses of low‐risk singleton pregnancies between 24 and 34 gestational weeks. The insular length or height increased with gestational age in the axial and coronal planes with adjusted R2 = 0.621, p < 0.0001 and R2 = 0.384, p < 0.0001, respectively. The SF depth also increased with gestational age in the axial and coronal planes with adjusted R2 = 0.695, p < 0.0001 and R2 = 0.219, p = 0.008, respectively. The extent of the coverage of the insula by the frontal and temporal lobes in the coronal plane increased with gestational age (adjusted R2 = 0.627, p < 0.0001 and R2 = 0.589, p < 0.0001, respectively). The interclass correlation coefficients of the intra‐ and inter‐rater reliability of the studied parameters ranged between 0.71 and 0.97. The cortical anomalies in the 19 fetuses were polymicrogyria (7), simplified gyral pattern (3), dysgyria (3), lissencephaly (2), cortical malformation related to tubulinopathy (1), brain atrophy (1), cortical dysplasia (1), and cobblestone malformation (1). Three of the fetuses had multiple cortical anomalies. In 17 of 19 (89%) cases, at least one of our 6 SF parameters was found to be out of the normal range. In the coronal plane, SF height and depth were measured below 2SD in 9 (47%) and 4 (21%) cases, respectively. In the axial plane, SF length and depth were out of the normal ranges in six (31.5%) and four (21%), correspondingly. In the coronal plane, the opercular coverage by the frontal and temporal lobes was below 2 SD in 10 (52%) and 11 (57%), respectively. The scoring of the SF operculization by Quarello et al. was abnormal in 8 cases (42%). The measurement of the SF angle according to Poon et al. was abnormal in 14 cases (74%). Conclusions The fetal SF is a complex developing structure th...

Sonographic Cortical Development and Anomalies in the Fetus: A Systematic Review and Meta-Analysis

“…A malformation of cortical development can be suspected because of the lack of visualization of a given structure, a reduced degree of folding of the fissure, or a smaller depth of the sulcus compared to what is expected for a given gestational age. In our daily practice, we usually measure Sylvian fissure length on a trans-thalamic plane tracing a vertical line perpendicular to the midline starting from the insula external border to the internal surface of the parietal bone; a parieto-occipital fissure is measured in a trans-ventricular plane at the point of maximum extension and symmetry compared to the contralateral fissure starting from the midline, avoiding the inclusion of cortical tissue in the measurement; a calcarine fissure was identified in a coronal view of the trans-cerebellar plane and measured by tracing a line from the apex of the fissure to the midline [22]. The findings from this systematic review showed that Sylvian and parieto-occipital fissures were visualized in all cases undergoing ultrasound assessment at the time of the anomaly scan, while calcarine fissures were detected in only half of the cases.…”