Hello @rebhof and welcome to Mayo Clinic Connect. You will notice that I have moved your post into an existing discussion that you can find here: https://connect.mayoclinic.org/discussion/infundibulum-or-aneurysm/

I'm wondering if your first sentence is from your medical chart and you are trying to decipher its meaning?

I am not a doctor, but if I take apart the words, this is what I get:
A 1.9 mm aneurysm versus infundibulum = The main importance of an infundibulum is that it may be mistaken for a saccular (berry) aneurysm (which is rounded and has the branch at its base). An infundibulum in most cases measures less than 3 mm. Unlike an aneurysm, an infundibulum is not believed to be a risk for rupture and subarachnoid hemorrhage

...projects caudally = relating to or being a tail

...from the supraclinoid segment = The supraclinoid (carotid-ophthalmic) segment of the internal carotid artery (ICA) under the Bouthillier classification is defined as the segment between the ophthalmic and posterior-communicating arteries.

...of the internal carotid artery. = The internal carotid arteries are branches of the common carotid arteries that bifurcate into the internal and external carotids at the level of the carotid sinus. [2] After this bifurcation, the internal carotids traverse through the base of the skull to reach the vital organs that they supply.

Does dissecting that help you better interpret the meaning? Have you asked your neurologist for a layman explanation?