A Practical Approach to the Fetal CNS - Part 3-2
How to Measure the Ventricular Atrium

If we are going to rely heavily on this measurement, we better make sure that we do it right!

Rules for Measuring the Lateral Ventricle

must measure in the true transaxial plane

• In order to know that you are truly transaxial, you must compare the calvarial bones and make sure they are symmetric

measure across the posterior glomus of the choroid

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measure perpendicular to the long axis of the ventricle

measure from inner wall to inner wall

• Remember that the ependyma is one cell layer thick, so whatever echogenic lines you are seeing are NOT ependyma and thus not part of the ventricular wall, so do not include it in your measurement

DO THIS

NOT THIS!

do we always have to measure?

• If the choroid fills, or nearly fills, the ventricular atrium, then the diameter is normal, and we do not feel the need to even perform a measurement

what is the normal size? we are 10 mm "absolutists"

• The average diameter of the ventricular atrium is 6.5 mm. 
  • 3 Std Deviations is 10.4 mm. To make it easier, many years ago Dr. Filly began using 10 mm as a cutoff
  • "I have been accused of being a 10 mm absolutist!" Anything 1o mm or above is abnormal and below is normal. 
  • Dr. Filly believes that this methodology does the most good while doing the least harm.
  • With this in mind, always remember that when you set an "upper limit of normal"
    • Normal patients will fall above that line and 
    • Abnormal patients will fall below that line