Aqueduct stenosis

Aqueductal stenosis (AS) is a the most common cause of congenital obstructive hydrocephalus, but can also be seen in adults as an acquired abnormality. 

Epidemiology

Aqueductal stenosis can be divided into congenital and acquired, with different aetiologies and thus different demographics. 

• congenital
  • aqueductal webs or diaphragms
  • gliosis
• acquired
  • extrinsic compression
    • tectal plate glioma
    • pineal tumour
    • posterior fossa tumour
    • cerebral vascular malformation
  • intrinsic
    • infection : meningitis / ventriculitis
    • subarachnoid haemorrhage (SAH)

Congenital aqueductal stenosis has an estimated incidence is at ~ 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. 

The remainder of this article focus on congenital aqueductal stenosis. 

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 enlarging head size, bulging fontanellles and gaping cranial sutures are seen. Setting sun phenomenon may also be present.

The usual symptoms and signs of raised intracranial pressure may also be present, including headache, vomiting, decreased conscious state. 

Radiographic features

Antenatal ultrasound

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

Better delineates the extent of obstructive hydrocephalus, with enlargement (often marked) of the lateral and third ventricles. The aqueduct may show funnelling superiorly.  The 4^th ventricle is not dilated. In cases of secondary obstruction the underlying abnormality may also be evident. 

An MRI CSF flow study is helpful.

Treatment and prognosis

Treatment is often either with a third ventriculostomy or VP shunting. There is small recurrence risk ( ~ 4%) for congenital cases even when it is not X linked.