Aqueductal stenosis is narrowing of the cerebral aqueduct. This is the most common cause of congenital obstructive hydrocephalus, but can also be seen in adults as an acquired abnormality.
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Epidemiology
Congenital aqueductal stenosis has an estimated incidence of ~1:5000 births although the reported range varies greatly (3.7:1,000,000 to 1:2000) 5. Rarely it may be inherited in an X-linked recessive manner (Bickers-Adams-Edwards syndrome) 5.
In adults, as an acquired abnormality, aqueductal stenosis has different aetiologies and thus different demographics related to them.
Clinical presentation
The clinical presentation depends on the severity and age of presentation as well as whether or not it is X-linked. In the infant with enlarging head size, bulging fontanelles and gaping cranial sutures are seen. Setting sun phenomenon may also be present. In X-linked form (Bickers-Adams-Edwards syndrome), which is associated with profound intellectual disability, clinical assessment would reveal bilateral adducted thumbs.
The usual symptoms and signs of raised intracranial pressure and chronic hydrocephalus may also be present, including headache, vomiting, decreased conscious state 3.
Adults with late-onset idiopathic aquedcutal stenosis more commonly have chronic onset of neurological symptoms 6.
Pathology
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congenital
aqueductal webs or diaphragms
gliosis
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acquired
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extrinsic compression
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intrinsic
infection: meningitis/ventriculitis
idiopathic (called late-onset idiopathic aqueductal stenosis) 6
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Radiographic features
Ultrasound
An antenatal exam can show features of fetal hydrocephalus with a near-normal posterior fossa. There can be secondary thinning of the cortical mantle as well as secondary macrocephaly.
MRI
MRI better delineates the extent of obstructive hydrocephalus with an enlargement (often marked) of the lateral and third ventricles. The aqueduct may show funnelling superiorly. The 4th ventricle is not dilated. In cases of secondary obstruction, the underlying abnormality may also be evident (e.g. web, tumour).
sagittal T2: the absence of flow-void signal intensity at the aqueductal level has been suggested as a sign of aqueductal stenosis 3
sagittal CISS: best demonstrates obstructing web
CSF flow study: decreased aqueductal stroke volume and peak systolic velocity
Treatment and prognosis
Treatment is often either with an endoscopic third ventriculostomy or ventriculoperitoneal shunting.
Recurrence risk for congenital cases is around 4% even when it is not X-linked.
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