Radiology, Vol 166, 691-692, Copyright © 1988 by Radiological Society of North America

ARTICLES

Fetal rhombencephalon: normal US findings

DR Cyr, LA Mack, DA Nyberg, TH Shepard and WP Shuman
Department of Radiology, University of Washington, Seattle 98195.

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.

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