Hypoplasia of the internal carotid artery

Case contributed by Dr Mark Hall


A young lady presented with a sudden onset headache and vomiting. Lumbar puncture was normal but MRI brain raised the possibility of right ICA dissection or hypoplasia. A CT angiogram was carried out.

Patient Data

Age: 35 years
Gender: Female

CT Carotid Angiogram

The aortic arch is normal in appearance.  The left vertebral artery arises from the arch as a normal anatomical variant.

The left common, internal and external carotid arteries are patent.  The right internal and external carotid arteries arise separately from the brachiocephalic trunk, with the right internal carotid artery being extremely small in diameter, measuring only 1.5 mm, although the vessel appears patent throughout.  The diameter of the carotid canal is reduced significantly, appearances are in keeping with congenital hypoplastic right ICA.

Patent and normal in course and size.

The MCA vessels are normal in caliber bilaterally. Foetal origin of the right PCA and prominent right P1 suggesting the right MCA is being supplied primarily from the posterior circulation.  Foetal origin of the left PCA, which is normal in caliber. Fenestrated ACOM.

Hypoplastic right internal carotid. No dissection.

Case Discussion

This case demonstrates a hyoplastic right internal carotid artery.  The narrow right carotid canal, foetal right PCA with prominent right P1 artery add further evidence towards this.  

Agenesis, aplasia, and hypoplasia of the internal carotid artery (ICA) are rare congenital anomalies, occurring in less than 0.01% of the population.

As in this case the most common type of collateral flow is through the circle of Willis.

Although this case is an incidental finding, recognition is important as it is associated with cerebral aneurysms and has an implication during carotid endarterectomy and transsphenoidal hypophyseal surgery.

PlayAdd to Share

Case information

rID: 51522
Published: 22nd Feb 2017
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

Updating… Please wait.

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

 Thank you for updating your details.