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Background <p>It is important to obtain an accurate volumetric characterization of fetal posterior fossa growth on magnetic resonance imaging (MRI).</p> Objective <p>This study analyzes the normal growth, sexual dimorphism, and lateral asymmetry of the fetal posterior fossa during the late second and third trimesters.</p> Materials and methods <p>A total of 100 fetuses (23–40&#xa0;weeks gestational age (GA)) with normal brain development were retrospectively included in this study. The bilateral posterior fossa, cerebellar hemisphere, and brainstem (including the midbrain, pons, and medulla oblongata) were manually segmented on in vivo fetal MRIs. Normal growth, sexual dimorphism, and lateral asymmetry were analyzed after the fossa volumes were obtained.</p> Results <p>The total, left, and right posterior fossa volumes all linearly increased with GA. The volume of the right posterior fossa was significantly greater than that of the left and increased slightly faster. The cerebellar volume exponentially increased with increasing GA. The right cerebellar volume was significantly greater than the left cerebellar volume. The bilateral cerebellar volume had a similar growth rate, which accelerated and increased more quickly than did that of the posterior fossa volume after 35&#xa0;weeks GA. The brainstem volume linearly increased with GA. The pontine volume increased the fastest, followed by the midbrain volume, and the medullary volume increased the slowest. The relationship between the volume of the cerebrospinal fluid in the posterior fossa and GA was described adequately by a second-order polynomial curve, which increased before 30&#xa0;weeks GA but gradually decreased after 35&#xa0;weeks GA. No sexual dimorphism was detected in any of the measurements.</p> Conclusions <p>The development of the fetal posterior fossa follows a specific spatiotemporal course, and volumetric measurements reveal structure-specific and GA-related changes with different rates and lateral asymmetries. These results are valuable for assessing normal fetal posterior fossa development in utero.</p> Graphical Abstract <p></p>

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Normal growth, sexual dimorphism, and lateral asymmetry of the fetal posterior fossa during the late second and third trimesters

  • 期刊论文

  • 发表日期：

    2026年2月7日

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  • Yingxin Chen,
  • Xue He,
  • Chengyu Zheng,
  • Yue Gao,
  • Min Li,
  • Shuwei Liu,
  • Zhonghe Zhang

摘要

Background

It is important to obtain an accurate volumetric characterization of fetal posterior fossa growth on magnetic resonance imaging (MRI).

Objective

This study analyzes the normal growth, sexual dimorphism, and lateral asymmetry of the fetal posterior fossa during the late second and third trimesters.

Materials and methods

A total of 100 fetuses (23–40 weeks gestational age (GA)) with normal brain development were retrospectively included in this study. The bilateral posterior fossa, cerebellar hemisphere, and brainstem (including the midbrain, pons, and medulla oblongata) were manually segmented on in vivo fetal MRIs. Normal growth, sexual dimorphism, and lateral asymmetry were analyzed after the fossa volumes were obtained.

Results

The total, left, and right posterior fossa volumes all linearly increased with GA. The volume of the right posterior fossa was significantly greater than that of the left and increased slightly faster. The cerebellar volume exponentially increased with increasing GA. The right cerebellar volume was significantly greater than the left cerebellar volume. The bilateral cerebellar volume had a similar growth rate, which accelerated and increased more quickly than did that of the posterior fossa volume after 35 weeks GA. The brainstem volume linearly increased with GA. The pontine volume increased the fastest, followed by the midbrain volume, and the medullary volume increased the slowest. The relationship between the volume of the cerebrospinal fluid in the posterior fossa and GA was described adequately by a second-order polynomial curve, which increased before 30 weeks GA but gradually decreased after 35 weeks GA. No sexual dimorphism was detected in any of the measurements.

Conclusions

The development of the fetal posterior fossa follows a specific spatiotemporal course, and volumetric measurements reveal structure-specific and GA-related changes with different rates and lateral asymmetries. These results are valuable for assessing normal fetal posterior fossa development in utero.

Graphical Abstract