Subarachnoid Space Measurements in the Second Trimester Using MR Imaging.

Area of Science:

• Neuroimaging
• Fetal Development
• Quantitative Anatomy

Background:

• The subarachnoid space (SAS) is a critical component of the developing fetal intracranial compartment.
• Fetal brain MRI is increasingly used for early diagnosis of central nervous system (CNS) diseases.
• Establishing age-based standards for normal SAS depth is essential for accurate interpretation of fetal neuroimaging.

Purpose of the Study:

• To provide 2D reference measurements for supratentorial subarachnoid spaces in healthy fetuses.
• To establish normative data for subarachnoid space depth between gestational weeks 19 and 27.
• To support the clinical and research applications of fetal brain MRI.

Main Methods:

• Cross-sectional study of 159 fetal brain MRIs (19-27 weeks gestation) without visible pathology.
• Measurement of frontal, insular, and inferior temporal SAS widths bilaterally.
• Creation of centile curves using Generalized Additive Modeling for Location, Scale and Shape (GAMLSS).

Main Results:

• Inter-rater reliability (ICC) ranged from 0.667 to 0.943.
• No significant differences in SAS measurements between left and right sides or between sexes were observed after accounting for age.
• A single reference chart was generated for each SAS measurement.

Conclusions:

• Fetal subarachnoid space depth demonstrates adaptation to the growing fetal calvarium during the second trimester.
• This study provides essential normative reference ranges for the supratentorial subarachnoid spaces.
• These data will aid in the clinical assessment and research of fetal brain development and pathology.