Fetal rhombencephalon: normal US findings.
Using ultrasound (US), the authors examined 25 embryos that were 8-10 menstrual weeks old for gestational age and the presence of a small cystic structure (3-4 mm) in the posterior aspect of the cranium. This structure was seen in all embryos. The US images of an in vitro embryo at 8 weeks menstrual age were also evaluated for anatomic correlation. Analysis of these US images determined that the cystic structure was the open rhombencephalon or hindbrain. Follow-up US studies or postpartum clinical examinations of the 25 in utero embryos demonstrated no abnormal posterior cranial cystic structures or neurologic deficits. This first-trimester structure should be considered a normal finding, since it develops into the normally proportioned fourth ventricle after the 11th menstrual week.
Cyr
D R
DR
Department of Radiology, University of Washington, Seattle 98195.
Mack
L A
LA
Nyberg
D A
DA
Shepard
T H
TH
Shuman
W P
WP
D005260:Female; D005333:Fetus / Q000033:anatomy & histology*; D006801:Humans; D011247:Pregnancy; D012249:Rhombencephalon / Q000033:anatomy & histology*; D014463:Ultrasonography