Aneurysm of Persistent Trigeminal Artery
CTA showing large aneurysm at the dorsal upper part of the right Internal Carotid Artery (arrow). There is also an anatomic variant in form of a Persistent Trigeminal Artery (PTA) on the left side which is also showing an aneurysm in its anterior medial part (arrowhead). Note hypoplastic Basilar Artery (long arrow), as another anatomic variant. There are reports in the literature of aneurysms accompanying PTA. This was an incidental finding.
Note same findings on the 3D volume reconstructions. (Images are mirrored L-R).
Same 3D reconstructions from anterior angle. In this case aneurysms are obvious and easy to find. However it is good to be sure to look for aneurysms in case of this anatomic variant.
You might also check my previous post about Persistent Trigeminal Artery.
Also, if you like anatomic variants, there is a case of Persistent Hypoglossal Artery.