Fetal Ventriculomegaly: Measurement of the Lateral Ventricle Atrium and Severity Thresholds
Why the Atrium is Measured
According to ISUOG Practice Guidelines (2020), measurement of the lateral ventricle atrium is recommended because multiple studies demonstrate that this is the most effective approach for assessing ventricular system integrity. Ventriculomegaly (VM) is a common marker of abnormal cerebral development.
Measurement Technique
Measurement is performed at the level of the glomus of the choroid plexus, perpendicular to the ventricular cavity. Calipers are placed within the echogenic signals generated by the lateral walls (ISUOG, 2020).
When diagnosing VM, calipers are positioned within the echogenic signals from the lateral walls of the posterior horn at the level of the parieto-occipital sulcus; a diameter >10 mm is diagnostically significant (ISUOG, 2024).
Diagnostic Threshold
| Parameter | Value | Source |
|---|---|---|
| Normal atrial width (example) | 5.3 mm (no signs of VM) | ISUOG, UOG 63(1), 2024 |
| Diagnostic threshold for VM | >10 mm | ISUOG, UOG 63(2), 2024 |
Specific numerical thresholds for distinguishing mild, moderate, and severe degrees are not provided in the source fragments — [clarification needed] according to current guidelines.
Prognostic Significance
Postnatal outcome in children with VM is determined primarily by the presence of associated anomalies (structural or genetic) and the degree of dilatation (ISUOG, UOG 63(2), 2024).
Timing of Detection
VM is typically diagnosed during routine second-trimester screening for fetal anomalies; however, it may also appear in the third trimester. A normal scan in the second trimester does not completely exclude this diagnosis (ISUOG, 2024).
Frequently asked questions
At what level and how should the atrium be measured?
At the level of the glomus of the choroid plexus, perpendicular to the ventricular cavity, with calipers placed within the echogenic signals from the lateral walls (ISUOG, 2020).
What diameter threshold is considered ventriculomegaly?
An atrial diameter >10 mm. Measurement is performed within the echogenic signals of the lateral walls of the posterior horn at the level of the parieto-occipital sulcus (ISUOG, 2024).
Does a normal second-trimester screening exclude VM?
No. VM may appear in the third trimester; a normal scan in the second trimester does not completely exclude this diagnosis (ISUOG, 2024).
What factors determine postnatal prognosis in VM?
Primarily the presence of associated structural or genetic anomalies and the degree of dilatation (ISUOG, UOG 63(2), 2024).
What are the exact thresholds that distinguish VM severity grades?
The numerical boundaries for mild, moderate, and severe degrees are not provided in the source fragments — [clarification needed]. Only the general diagnostic threshold of >10 mm is specified.