The fetal posterior fossa: clinical correlation of findings on prenatal ultrasound and fetal magnetic resonance imaging.

Objectives: Recognize posterior fossa anomalies on ultrasound and magnetic resonance imaging and appreciate imaging pitfalls that may lead to misdiagnosis.

Materials And Methods: Cases are presented to illustrate normal development and various anomalies. Postnatal studies and autopsy are used for correlation with prenatal imaging.

Results: Normal anatomy and anomalies are demonstrated. Pitfalls such as cystic hygroma, pseudomasses, and use of nonstandard scan planes are illustrated.

Conclusions: Recognizing normal developing structures is an important component of performing fetal ultrasound. Documentation of the cerebellum, vermis, and cisterna magna are required for posterior fossa evaluation in any American Institute of Ultrasound in Medicine-certified practice. Normal variations are common, and understanding the anatomy is vital to avoid misdiagnosis and to accurately characterize abnormalities.