Overview

• Cerebral ventriculomegaly: enlargement of lateral ventricles, common fetal neurological finding.
• Prevalence: Up to 1% of fetal ultrasound scans.
• Importance: Leading cause for fetal neurological consultation.

Definition and Classification

Measurement:

• Lateral ventricular atrium diameter on axial ultrasound view.
• Normal ventricular diameter stable at ~6–7 mm between 14 weeks and term.
• Ventriculomegaly diagnosed when ventricular atrium measures ≥10 mm.

Severity Classification:

• Mild Ventriculomegaly: 10–12 mm
• Moderate Ventriculomegaly: 12–15 mm
• Severe Ventriculomegaly: >15 mm (less common)

Laterality:

• Unilateral vs. bilateral
• Symmetrical vs. asymmetrical

Course:

• Transient: spontaneously resolves
• Stable: no significant change
• Progressive: increases over time

Etiology and Pathogenesis

General Mechanisms:

• Obstructive Hydrocephalus (CSF flow blockage):
  • Aqueductal stenosis (aqueduct of Sylvius blockage)
  • Fourth ventricular foraminal obstruction (e.g., Dandy-Walker malformation, Chiari malformations)
• Ex vacuo ventriculomegaly (brain tissue loss or hypoplasia):
  • Cerebral atrophy, infarction, infections, genetic syndromes.

Obstructive Ventriculomegaly (Hydrocephalus):

• Aqueductal stenosis: enlarged lateral and third ventricles, normal-sized fourth ventricle.
  • Causes: dysgenesis, webs, membranes, tumors, infections (toxoplasmosis, CMV, parvovirus B19).
• Tetraventricular hydrocephalus: blockage at fourth ventricle foramina (Magendie/Luschka).
  • Causes: Chiari II malformation, Dandy-Walker malformation, posterior fossa cysts or masses.
• Transient hydrocephalus: may result from delayed fenestration of Blake’s pouch cyst.

Associated Conditions and Syndromes

CNS Infections:

• Cytomegalovirus (CMV): ventriculomegaly often associated with calcifications, cortical anomalies, periventricular halo.
• Toxoplasmosis: rare, aqueductal stenosis common.
• Parvovirus B19: mild ventriculomegaly possible.

Genetic and Chromosomal Syndromes:

• Chromosomal anomalies (aneuploidy, especially trisomy) rare with mild ventriculomegaly (≤15 mm, ~5%); more frequent (>15%) when associated anomalies present.
• Callosal dysgenesis: characteristic "colpocephaly" (enlarged occipital horns).
  • Present in ~13% of fetal ventriculomegaly cases.

Structural Brain Malformations:

• Cortical malformations (lissencephaly, schizencephaly).
• Posterior fossa malformations (Dandy-Walker, Chiari).

Differential Diagnosis

• Hydranencephaly (severe hemispheric destruction)
• Holoprosencephaly (abnormal midline prosencephalic cleavage)
• Enlarged cavum septi pellucidi or cavum velum interpositum cyst.

Prognostic Factors

• Severity of ventriculomegaly (most crucial)
• Etiology (hydrocephalic vs. ex vacuo vs. genetic)
• Associated brain anomalies significantly impact outcomes.
• Progression (stable vs. progressive)
• Presence of syndromic or chromosomal abnormalities

Prognostic Categories:

• Serial ultrasound scans essential for monitoring progression.

Imaging Approaches and Challenges

Fetal Ultrasound:

• Highly sensitive for initial diagnosis and monitoring.
• Limited in detecting subtle associated anomalies.

Fetal MRI:

• Recommended for further characterization, etiological clarification, and identification of subtle anomalies.
• Additional yield of MRI-detected anomalies:
  • 5%–60% depending on ventricular size.
• Postnatal MRI further identifies anomalies in 10–28% of cases initially classified as isolated on fetal imaging.

Clinical Outcomes and Counseling

Mild isolated ventriculomegaly (≤15 mm):

• High rate of favorable outcomes; majority neurologically normal.
• Persistent mild ventriculomegaly at 2 years may slightly increase risks for subtle language and motor delays.

Moderate to Severe or Associated Ventriculomegaly:

• Often significant neurodevelopmental impairments.
• Associated anomalies significantly worsen prognosis.

Clinical Recommendations

• Detailed fetal neuroimaging (MRI) when ventriculomegaly is detected.
• Serial ultrasound examinations to monitor ventricular size and progression.
• Early postnatal MRI if ventriculomegaly persists.
• Neurological follow-up: developmental assessment and support, especially for moderate-severe cases