Ventriculomegaly is a brain condition that occurs in about 0.1% of pregnancies. It is typically defined by the width of the atrium of the lateral ventricle of greater than 10 mm.

When this measurement is between 10 and 15 mm, the ventriculomegaly may be described as mild to moderate. When the measurement is greater than 15mm, the ventriculomegaly may be classified as more severe. 

It may occur for a number of reasons and fften there is no identifiable cause as to the enlargement of the ventricles, it could be as a result of a loss of brain volume, or impaired outflow cerebrospinal fluid from the ventricles, or thier may have been an obstruction caused by an infection. This diagnosis is generally found in routine fetal anomaly scans at 18–22 weeks gestation.

http://en.wikipedia.org/wiki/Ventriculomegaly

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