Measure the atrium of the lateral ventricle correctly (≥ 10 mm is ventriculomegaly), then search for its cause — spina bifida, aqueduct stenosis, callosal agenesis, infection, haemorrhage — because isolated mild ventriculomegaly and associated ventriculomegaly have very different outcomes.
Orient first
- Mild 10–12 mm, moderate 13–15 mm, severe > 15 mm (verify the grading your service uses).
- Measure in the transventricular axial plane at the level of the glomus of the choroid plexus, callipers on the inner margins, perpendicular to the ventricle.
- Fetal MRI finds associated anomalies in a proportion of apparently isolated cases.
Acquire the study
- Transventricular axial plane; transvaginal neurosonography for sagittal and coronal planes in cephalic fetuses.
The manoeuvre
- Atrial width in mm, inner-to-inner, perpendicular to the ventricle at the glomus.
- Both ventricles (the near one is obscured by reverberation).
- Cavum septi pellucidi and corpus callosum in the mid-sagittal plane.
- Spine and posterior fossa (banana and lemon signs) — exclude spina bifida.
- Periventricular echogenicity or calcification (infection), intraventricular echogenic clot (haemorrhage).
What confirms it
- Atrial width ≥ 10 mm measured to standard, with the associated findings listed.
What licenses you to exclude it
- Atrial width < 10 mm on a correct plane is normal.
The classic misread
- Measuring on an oblique plane or at the occipital horn — overcalls.