Fetal ventriculomegaly: atrial measurement, grades and what to write in the report

Fetal ventriculomegaly is defined by a lateral ventricular atrial width of 10 mm or more, and ISUOG considers a measurement below 10 mm normal throughout pregnancy. The number alone does not settle the diagnosis: the report needs a correct measurement, the side, the grade and what else was assessed.

How to measure the atrium

• Axial transventricular plane, assessing the atrium distal to the transducer.
• Measure at the level of the glomus of the choroid plexus, perpendicular to the ventricular axis, at its widest part.
• Calipers on the inner edge of the walls (inner to inner).
• The mean is 6 to 8 mm, stable in the second and early third trimesters.
• Per ISUOG, moderate asymmetry is normal if both atria measure under 10 mm. The width may increase or decrease during pregnancy.

Grades of fetal ventriculomegaly: ISUOG and SMFM

The ISUOG screening guideline (Part 1) does not grade: it treats 10 mm or more as suspicious and points to targeted neurosonography. The grading below comes from SMFM, which suggests it for counseling, and from clinical series, which do not use exactly the same limits.

Because the limits differ between sources, always give the measurement in millimeters next to the grade.

Associated workup

• Anatomy: detailed examination by an experienced practitioner, including ventricles, corpus callosum, cerebellum, heart and growth.
• Genetics: SMFM recommends offering amniocentesis with chromosomal microarray. About 5% of apparently isolated mild to moderate cases have an abnormal karyotype, and another 10 to 15% have abnormal microarray findings.
• Infection: testing for cytomegalovirus and toxoplasmosis regardless of symptoms or exposure.
• MRI: SMFM suggests considering it in mild and moderate cases, with less yield after an expert scan. ISUOG advises that it be indicated by the expert who performed the neurosonography, not solely on suspicion at screening.
• Follow-up: serial ultrasound to show progression, stability or resolution. Timing and mode of delivery follow standard obstetric indications.

Prognosis

Per SMFM, in isolated cases the likelihood of normal neurodevelopment is above 90% at 10 to 12 mm and 75 to 93% at 13 to 15 mm. The Pagani meta-analysis, which defined mild as 10 to 15 mm, found delay in 7.9% of isolated cases. A normal variant can only be diagnosed by exclusion after birth, so "isolated" in a report means only that no other finding has been seen so far.

What the report should include

• Width of each atrium in mm and gestational age.
• Side (unilateral, bilateral, asymmetric) and grade.
• Appearance of the horns and of the third and fourth ventricles, when assessed.
• Corpus callosum, posterior fossa and other structures, or what could not be characterized.
• Comparison with any prior scan.
• Sample impression: "Mild right ventriculomegaly (atrial width 11 mm), with no other anomaly identified on the current scan."

Common mistakes

• Placing the calipers mid-wall or on the outer wall.
• Measuring behind the glomus, where the ventricle is narrower, or off the perpendicular.
• Assessing only the distal atrium after finding dilatation, without describing the other side.
• Writing the grade without the measurement.
• Calling it isolated or benign before the full workup.

See also our articles on the second-trimester anomaly scan report and transfontanelle ultrasound.

How Laudário helps

In the fetal neurosonography template in Laudário:

• Right and left atrium in separate fields, with the class (normal, mild, moderate, severe) shown as you type.
• Horns, choroid plexuses, aqueduct and the isolated ventriculomegaly option flow into the text and the impression.
• In the second-trimester anomaly scan, the atrial measurement also adjusts the ventricle sentence and the impression; there the moderate band runs from above 12 up to 15 mm.

Try it free for 15 days, no credit card required.

References

• Malinger G, et al. ISUOG Practice Guidelines (updated): sonographic examination of the fetal central nervous system. Part 1. Ultrasound Obstet Gynecol. 2020;56:476-484.
• SMFM, Fox NS, et al. Consult Series #45: Mild fetal ventriculomegaly: diagnosis, evaluation, and management. Am J Obstet Gynecol. 2018;219(1):B2-B9.
• Gaglioti P, et al. Fetal cerebral ventriculomegaly: outcome in 176 cases. Ultrasound Obstet Gynecol. 2005;25:372-377.
• Pagani G, et al. Neurodevelopmental outcome in isolated mild fetal ventriculomegaly: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2014;44:254-260.