A Practical Approach to the Fetal CNS - Part 4
The Cisterna Magna

Take Home Points

is a measurement of the cisterna magna always required?

• We certainly have nothing against measuring the cisterna magna whenever you want
• However, in our opinion, it is not necessary if you see CSF going behind the cerebellum and surrounding the cerebellar hemispheres

What does visualizing a normal cisterna magna do for us?

• A ventricular measurement < 10 mm excludes all of these!

how does an abnormal cisterna magna help us?

• In the lateral ventricle section, we noted that an enlarged lateral ventricle identified 88% of fetal CNS anomalies. The addition of an abnormal cisterna magna increases that to 95%

dandy walker and chiari (examples)

• Remember that the "banana sign" in myelomeningocele indicates a moderate chiari malformation. It may be much more subtle with just effacement of the fluid.

DISCERNING AN ABNORMAL CISTERNA VS. TECHNICAL DIFFICULTY

•  If you are going to ascribe the lack of visualization to a technical problem, make sure it is on this list! Otherwise try try again!