Ultrasound investigation of the posterior fossa in the fetus.

One hundred and thirty normal pregnancies, ranging in gestational age from 15 to 40 weeks, were investigated to evaluate the capability of ultrasound to demonstrate the anatomy of the fetal posterior fossa. The cerebellum, including the cerebellar hemispheres, the superior and inferior vermis, the fourth ventricle, and the cisterna magna could be demonstrated easily. The ultrasound interpretation of the brain structures was verified by the anatomic dissection of the brains of 10 stillborn premature infants. A systematic approach to the prenatal ultrasound examination of the posterior fossa is described.