Ultrasound features of anencephaly
Anencephaly is one of the most common neural tube defects with a frequency of 1 in 1000. The fetal skull and cerebral cortex are absent while the skull base, brainstem, and orbits remain.
US can depict absence of the calvarium and brain above the orbits as early as 8 weeks gestation, but definitive diagnosis should be reserved for when the calvarium should be ossified at 14 weeks. In some instances, dysmorphic “angiomatous stromal” tissue may be seen above the brainstem.
