First Trimester Anatomy that May Mimic Fetal Anomaly
Fetal rhombencephalon- The rhomboid fossa of the normally developing rhombencepliaion can appear as a small (3—4 mm) ‘cystic’ structure in the posterior aspect of the cranium, between 8 and 10 weeks menstrual age. It should not be confused with an abnormal cystic posterior fossa structure e.g. Dandy—Walker malformation
Telecephalic and mesemcephalic vesicles- Also appear at about 7 weeks
Physio1ogic mid gut herniation- Appears at about 8 weeks and may persist until 12 weeks in 20% of normal fetuses.
The umbilical cord may be the site of cysts, varying from 2 to 7 mm, in under I % of normal pregnancies
