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Basilar Artery Fenestration

Summary

  • Basilar artery fenestration is a rare vascular anomaly characterised by the splitting of the basilar artery into two separate channels that later reunite
  • Associated with increased risk of aneurysm formation and subarachnoid haemorrhage
  • Typically asymptomatic and discovered incidentally on imaging studies1

Anatomy

  • The basilar artery divides into two separate lumens which reunite distally
  • Results from incomplete fusion of the paired longitudinal neural arteries during embryonic development
  • Can occur at any point along the basilar artery, but most commonly in the proximal segment
  • The fenestrated segment has weakened vessel walls and altered haemodynamics

Imaging

  • Digital Subtraction Angiography (DSA):
    • Gold standard for diagnosis
    • Demonstrates two separate lumens with reunification
  • CT Angiography (CTA):
    • High-resolution imaging can detect fenestrations
    • May be limited by bone artefacts at the skull base
  • MR Angiography (MRA):
    • Time-of-flight (TOF) and contrast-enhanced techniques can visualise fenestrations
    • Less sensitive than CTA or DSA for small fenestrations
  • 3D rotational angiography:
    • Provides detailed visualization of vascular anatomy
    • Useful for surgical or endovascular planning

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  • After the confluence of the vertebral arteries, the basilar artery diverges before merging at its mid-segment.

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  • Left PCA thrombus (red arrow) caused a left occipital infarct.
  • There was a proximal basilar artery fenestration.

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Clinical Relevance

  • Prevalence estimated at 0.6-2.3% in angiographic studies, typically discovered in adulthood during imaging for unrelated conditions
  • Incidental fenestrations need no treatment
  • The weakened wall and altered haemodynamics predispose to aneurysm formation, classically at the proximal fenestration limb; any associated aneurysm may present with subarachnoid haemorrhage and is treated on its own merits
  • Rarely associated with ischaemic events due to thrombus formation within the fenestration

Differential diagnosis

Differential Diagnosis Differentiating Feature
Basilar artery dissection Absence of intimal flap or double lumen on imaging
Vertebrobasilar dolichoectasia Elongation and dilatation of basilar artery without focal splitting
Basilar artery aneurysm Focal outpouching rather than longitudinal splitting of the artery
Arteriovenous malformation Absence of abnormal arteriovenous connections on angiography
Basilar artery thrombosis Lack of filling defect or occlusion on vascular imaging
Persistent trigeminal artery Different anatomical location and connection to carotid artery
Basilar artery hypoplasia Uniformly small caliber without focal duplication
Basilar artery atherosclerosis Absence of focal arterial wall thickening or stenosis
Vasculitis Lack of multifocal arterial narrowing or beading appearance
Basilar artery duplication Complete separation of two basilar arteries along entire course

  1. Styczen et al. Reconstructive endovascular treatment of basilar artery fenestration aneurysms: A multi-centre experience and literature review. 2022. The neuroradiology journal - Open in new tab. ↩