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Updated: Aug 11, 2026
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State of the Art Cranial Ultrasound Imaging in Neonates
Published on: February 2, 2015
The Diencephalon/Falx Ratio: A Novel Mid-Sagittal Marker for First-Trimester Neurosonography
Oscar Lavalle López1,2, Rogelio Cruz Martínez3, Miguel Martínez3
1Department of Maternal-Fetal Medicine, Medifetal, Cartagena, Colombia.
Journal of Clinical Ultrasound : JCU
|August 9, 2026
Summary
This study establishes normative reference ranges for fetal diencephalon and falx cerebri measurements in early pregnancy. These measurements aid in comprehensive first-trimester fetal neurosonographic assessments.
Area of Science:
- Fetal Medicine
- Neurosonography
- Developmental Biology
Background:
- Accurate fetal anatomical assessment in the first trimester is crucial for early detection of anomalies.
- Establishing normative data for fetal brain structures aids in interpreting developmental variations.
Purpose of the Study:
- To determine normative reference ranges for diencephalon diameter, falx cerebri length, and their ratio.
- To evaluate the relationship between these measurements and crown-rump length (CRL).
- To assess the utility of these measurements in identifying fetal midline anomalies.
Main Methods:
- Prospective observational study of 676 fetuses during first-trimester screening.
- Standardized mid-sagittal plane measurements of diencephalon and falx cerebri.
- Quantile regression used to generate 5th, 50th, and 95th percentile curves based on CRL.
Main Results:
- Diencephalon diameter increased progressively with CRL; falx cerebri length showed modest growth.
- The diencephalon/falx (D/F) ratio exhibited a slight inverse relationship with CRL.
- Two cases of agenesis of the corpus callosum were noted, with an abnormal D/F ratio in one.
Conclusions:
- Diencephalon and falx measurements are reproducible in the first trimester.
- Quantile-based nomograms offer a normative framework for these measurements.
- The D/F ratio alone has limitations in detecting certain midline anomalies; use as an adjunctive marker in comprehensive neurosonography is recommended.
