Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine you and obtain a history and review your imaging, I can not tell you what the exact implications of your imaging findings are. However I will try to provide you with some useful information.
The brain has two main blood supplies: anterior circulation and posterior circulation. The vertebral arteries branch off the subclavian arteries to form part of the posterior circulation. In many people, one of the two vertebral arteries is hypoplastic: developmentally smaller than the other side. Hypoplasia would be unlikely to form in young adulthood, it is there developmentally. However, if it is subtle it may not have been noticed by prior radiology interpretation, or sometimes the cuts the MRI makes of the brain may not have allowed for good visualization of portions of it; MRI is not ideal for assessment of the arteries, rather, an MRA or other vascular imaging is needed. Sometimes, tears in the arteries (dissections) due to trauma and other causes can lead to narrowing of one of the arteries, but this can be distinguished radiologically, because a hypoplastic artery is narrow throughout its course where as a dissected artery, or one narrow due to some other process, would more likely be affected in a segment or patch segments.
The two vertebral arteries join to form another artery, the basilar artery, which provides blood to the brainstem. As long as one of the two vertebral arteries is of sufficient size, there is not a particular risk of stroke due to hypoplastic artery; in fact, some believe the artery is hypoplastic because the other one is dominant.
It is important to understand the implications of your imaging findings and discussion of your questions with your neurologist is important.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
I waould also like to ask, if right vertebral artery hypoplasia, could make breathing seem diffucult. I get these times when it feels really hard to breathe over the past year. During these times, my blood oxygen is always 100%, and I can blow the needle off the spriometry. Just asking, as my breathing problem has been undiagnosed, with the exception my gerd and a 5cm hitial hernia causing it.
I also have slight left sided facial numbness. Trigeminal nerve. Had 2 MRI's-MRA's for that nothing found. This numbness has been here for over 2 years before this headache-dizzyness problem that I am currently having.