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Sylvian aqueduct stenosis

Summary

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  • Sylvian aqueduct stenosis is a congenital or acquired narrowing of the cerebral aqueduct
  • Results in obstructive hydrocephalus due to impaired CSF flow from the third to fourth ventricle
  • Characterised by ventriculomegaly on imaging, with a dilated third ventricle and normal-sized fourth ventricle

Pathophysiology

  • Congenital causes:
    • Developmental abnormalities of the aqueduct
    • Genetic factors (e.g., X-linked hydrocephalus)
  • Acquired causes:
    • Inflammation or infection (e.g., toxoplasmosis, viral infections)
    • Tumours compressing the aqueduct
    • Haemorrhage or gliosis
  • Results in:
    • Increased intracranial pressure
    • Progressive ventriculomegaly
    • Potential neurological deficits

Demographics

  • Congenital form:
    • More common in males (X-linked hydrocephalus)
    • Often diagnosed prenatally or in early infancy
  • Acquired form:
    • Can occur at any age
    • Incidence increases with age due to higher risk of tumours and vascular events

Diagnosis

  • Clinical presentation:
    • Infants: macrocephaly, bulging fontanelle, developmental delay
    • Adults: headache, gait disturbances, cognitive decline, urinary incontinence
  • Neurological examination:
    • Papilledema
    • Upward gaze palsy (Parinaud syndrome)
    • Ataxia
  • Ophthalmological assessment:
    • Fundoscopy to evaluate for papilledema

Imaging

  • CT:
    • Ventriculomegaly of lateral and third ventricles
    • Normal-sized fourth ventricle
    • Possible periventricular hypodensity (transependymal CSF absorption)
  • MRI:
    • Gold standard for diagnosis
    • T1-weighted and T2-weighted sequences:
    • Dilated lateral and third ventricles
    • Narrowed or obliterated aqueduct
    • Normal-sized fourth ventricle
    • CISS/FIESTA sequences:
    • High-resolution imaging of the aqueduct
    • Phase-contrast MRI:
    • Evaluation of CSF flow dynamics
  • Cine MRI:
    • Demonstrates aqueductal CSF flow obstruction

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  • A 50-year-old patient had progressive gait disturbance and more recent upper limb clumsiness.
  • The lateral and third ventricles were very enlarged without periventricular oedema.
  • A web in the inferior Sylvian aqueduct, better seen on CISS than T1 (red arrow), was causing impaired CSF outflow.

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  • A 50 year old presented with a chronic headache and gait disturbance.
  • MRI showed ventriculomegaly with a periventricular rim of T2-hyperintense oedema.
  • CISS imaging showed a filling defect in the superior Sylvian aqueduct likely to represent a web.
  • CSF flow studies did not show pulsatile CSF flow across through the Sylvian aqueduct.

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  • A 40-year-old patient had an MRI scan due to chronic but increasing headaches.
  • MRI showed a focal filling defect in the inferior Sylvian aqueduct.
  • CSF flow studies showed normal biphasic flow indicating a stenosis rather than an obstruction.

Treatment

  • Medical management:
    • Acetazolamide to reduce CSF production (temporary measure)
    • Treatment of underlying causes (e.g., infections, tumours)
  • Surgical interventions:
    • Endoscopic third ventriculostomy (ETV):
    • First-line treatment in many cases
    • Creates alternative CSF pathway
    • Ventriculoperitoneal (VP) shunt:
    • Alternative to ETV or in cases of ETV failure
    • Aqueductoplasty:
    • Endoscopic procedure to restore aqueduct patency
  • Follow-up:
    • Regular neuroimaging to assess ventricular size
    • Neurological and developmental assessments
    • Shunt function monitoring (if applicable)

Differential diagnosis

Differential Diagnosis Differentiating Feature
Aqueductal web Thin membrane visible on high-resolution MRI
Tectal glioma Presence of a mass lesion in the tectal plate on MRI
Pineal region tumour Visible mass in the pineal region on imaging studies
Dandy-Walker malformation Cystic dilatation of 4th ventricle and cerebellar vermis hypoplasia
Chiari malformation Downward displacement of cerebellar tonsils on MRI
Benign intracranial hypertension Normal or small ventricles on imaging
Communicating hydrocephalus Enlargement of all ventricles without obvious obstruction
Arachnoid cyst Well-defined, extra-axial CSF-density lesion on CT/MRI
Vein of Galen malformation Dilated vein of Galen visible on angiography or MRI
Craniosynostosis Premature fusion of cranial sutures on CT