Presentation
Abdominal pain. Normal first trimester ultrasound at 8 weeks 4 days.
Patient Data

There is a prominent cystic region in the posterior aspect of the embryonic head. This is compatible with the normal fetal rhombencephalon. Smaller round hypoechoic focus represents forebrain.

A blue arrow points to a prominent cystic region in the posterior aspect of the embryonic head. This is compatible with 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.