Fetal Aqueductal Stenosis (Obstructive Hydrocephalus)

Step-by-step decision

Choose step by step as prompted; reaching an endpoint gives the management recommendation. You can go back a step or restart anytime.

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Full pathway

1. [Decision] Lateral/third ventricle + fourth ventricle + aqueduct signs
   Lateral/third ventricle dilation + fourth ventricle + aqueduct signs? (Aqueductal stenosis = non-communicating hydrocephalus (aqueduct obstruction) → lateral + third ventricle dilation with a normal fourth ventricle (key differentiation). Progressively raised ICP, ventricles often progressively enlarge.)
   • Lateral + third ventricle dilation, normal fourth ventricle, funnel-shaped aqueduct/intra-aqueductal blood or web → Aqueductal stenosis · check L1CAM/cause
   • All ventricles (including fourth) dilated or posterior fossa abnormality (communicating/other cause) → All ventricles dilated/posterior fossa abnormality · differentiate cause
2. [End] Aqueductal stenosis · check L1CAM/cause
   Aqueductal stenosis (lateral + third ventricle dilation, normal fourth ventricle): high-PPV fetal MRI signs — enlarged third ventricle inferior recesses, funnel-shaped aqueduct with distal obstruction, callosal abnormality, ventricular diverticulum, intra-aqueductal hemorrhage/web, septum pellucidum absence; check X-linked L1CAM (male, adducted thumbs, family history), post-hemorrhagic, infection (CMV/toxoplasma); monitor progressive ventricular enlargement and cortical mantle thickness (prognosis); multidisciplinary counselling, postnatal shunt/ETV.
3. [End] All ventricles dilated/posterior fossa abnormality · differentiate cause
   All ventricles (including fourth) dilated or posterior fossa abnormality: suggests communicating hydrocephalus or another cause (hemorrhage/infection/Dandy-Walker/Chiari II); fetal MRI to differentiate the obstruction level and cause, manage along the relevant pathway (posterior fossa/hemorrhage/infection) + chromosomal and infection assessment.

Source guidelines & references

• Congenital aqueductal stenosis fetal MRI signs (AJNR 2018; L1CAM)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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