A1 segment hypoplasia

Case contributed by Dr Mostafa El-Feky


Right sided numbness

Patient Data

Age: 25 years
Gender: Female



Normal MRA of the brain. The following anatomical variants are noted:

  • absent A1 segment of right anterior cerebral artery. A2 segment is perfused through Acom artery
  • fetal origin of right posterior cerebral artery, from right Pcom artery
  • dominant left vertebral artery

Case Discussion

Cerebral MR angiography shows absent right A1 segment, a common variant of circus of willis accounting for 10% of individuals. The contralateral A1 segment supplies ipsilateral A2 segment by a prominent anterior communicating artery.

Fetal origin of right posterior cerebral aretry also incidentally noted, a common variant of the posterior cerebral circulation in which a prominent ipsilateral PCOM supplies the posterior cerebral artery rather than basilar artery. 

This study was done in conjunction with a brain MRI study which was normal.

How to use cases

You can use Radiopaedia cases in a variety of ways to help you learn and teach.

Creating your own cases is easy.

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.