Basilar Fenestration-MRA

18 yr old girl presented with  seizure and altered sensorium, with MRI showing cytotoxic oedema of Pons with mass effect on 4th ventricle with MRA suggesting irregular caliber of basilar artery in proximal and middle one third with right vertebro basilar junction appearing irregular. Though not classical  in appearance , basilar fenestration leading to thrombosis and infarction  was  suggested  in view of age of the patient.

Teaching points by Dr MGK Murthy, Dr GA Prasad, Mr Venkat

• The Word  fenestration refers to localized  or segmental duplication  equivalent  to an unfused vessel.  Basilar artery constitutes a  common area for fenestration amongst the intracranial vessels 
• Basilar Artery  is formed in first stage  from  paired  primitive longitudinal neural arteries (at 45 mm embryo stage). Second stage they develop focal connections and then fusion starts (5th week of gestation). If they fail to fuse, leads to fenestration and is a  rare anomaly (Autopsy series 1.3 to 5.3 percent versus DSA  0.6 to 1.7 percent and MRA even less because of  lack of high resolution) 
• Black teal reported endothelium lining partitions  like intraluminal septae akin to spurs ,  triggering thrombosis and leading to strokes in young. Media is absent at the site with  discontinuity of elastin at proximal end of fenestration with sub endothelium thickened distally and thinned proximally  leading to haemodynamic disturbance  forming aneurysms locally 

Useful  classification refers to its relationship to AICA:

1. Type 1=fenestration proximal to AICA
2. Type 2- Bilateral AICAs arising from it symmetrically 
3. Type 3=unilateral AICA arising from the fenestrated segment
4.  Type 4=  fenestration Distal to AICA