Embryonic/fetal rhombencephalon

The embryonic/fetal rhombencephalon is visible with endovaginal ultrasound at ~8-10 weeks as a hypoechoic region in the embryonic/fetal head. The hypoechoic region represents the developing rhombencephalon/hindbrain (medulla, pons, and cerebellum).

This is a normal structure, and is reportedly visible in all embryonic/fetal exams at 8-10 weeks 2. It becomes a normal fourth ventricle after the 11th week.

Ultrasound - obstetric
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Article Information

rID: 33060
System: Obstetrics
Section: Anatomy
Synonyms or Alternate Spellings:
  • Fetal rhombencephalon
  • Fetal hindbrain
  • Embryonic rhombencephalon
  • Cystic rhombencephalon
  • Rhombencephalic vesicle

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Cases and Figures

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    Case 1: fetal rhombencephalon
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    Case 2: fetal rhombencephalon (8w 4d)
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