Fetal rhombencephalon

Case contributed by Dr Matt A. Morgan


Normal first trimester ultrasound of age corresponding to 8 weeks and 5 days


The fetal rhombencephalon is the anechoic structure in the posterior part of the brain. This is a normal appearance at 8-10 weeks, and should not be misinterpreted as a developmental problem.

Annotated image

The blue arrow points to a hypoechoic area in the fetal brain, the normal fetal rhombencephalon.

Case Discussion

The fetal rhombencephalon (also known as the "embryonic rhombencephalon" or "cystic rhombencephalon") is a normal finding in an embryo/fetus at 8-10 weeks of age. It should not be considered a developmental abnormality.

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