Brief Answer:
Your sister is right All Parts of Brain Get Blood From Both Arteries

Detailed Answer:
Hi,

Welcome to HealthCareMagic.com I am Dr.J XXXXXXX Anto Bruno Mascarenhas. I have gone through your query with diligence and would like you to know that I am here to help you.

Question : So who's right - the neurologist or my sister.
Answer : Your Sister is Right

Please see http://teachmeanatomy.info/wp-content/uploads/Schematic-of-the-Circle-of-Willis.jpg

You can Arteries marked in Red and a section of those marked in yellow. This yellow part is called as Circle of Willis. Thus there is a communication between the Posterior Circulation (Vertebral and Basilar arteries) and Anterior Circulation (Carotid Arteries)

So, in essence,
All Parts of Brain Get Blood From Carotid Arteries through circle of Willis
All Parts of Brain Get Blood From Vertebral Arteries through circle of Willis
All Parts of Brain Get Blood From Both Arteries through circle of Willis

-oOo-

Now, having answered your question, let me add something more

You had a stroke last summer that affected my vision and memory.
This can very well due to Obstruction in Carotid Arteries Or Anterior Circulation Stroke. Carotid Arteries supply Ophthalmic Artery - The artery to Optic Nerve and Orbit - and hence you can get visual disturbance even when Occipital and Parietal Lobes are not involved. Memory can be affected due to Anterior Circulation Stroke too

So,
In a nut shell, I think your vascular surgeon and your sister are both on target.

Hope you found the answer helpful.

If you need any clarification / have doubts / have additional questions / have follow up questions, then please do not hesitate in asking again. I will be happy to answer your questions.

Best Wishes for Speedy Recovery
Let me know if I can assist you further.
Take care.

-oOo-

PS 1 : After all your doubts have been cleared, kindly (a) Close this Question (b) Rate my Replies and (c) Give your Feedback.

PS 2 : In the future, for continuity of care, I encourage you to contact me directly in HealthCareMagic at http://bit.ly/askdrbruno

---

Brief Answer:
Plaque breaking off from one of the carotid arteries is possible

Detailed Answer:
Dear Sir

Welcome Back

As I had told, it is perfectly possible for a plaque breaking off from one of the carotid arteries to cause a stroke in which you had memory disturbances and vision disturbances

Hope you found the answer helpful.

If you need any clarification / have doubts / have additional questions / have follow up questions, then please do not hesitate in asking again. I will be happy to answer your questions.

Best Wishes for Speedy Recovery
Let me know if I can assist you further.
Take care.

-oOo-

PS 1 : After all your doubts have been cleared, kindly (a) Close this Question (b) Rate my Replies and (c) Give your Feedback.

PS 2 : In the future, for continuity of care, I encourage you to contact me directly in HealthCareMagic at http://bit.ly/askdrbruno

---