I spoke with Dr. B today after he presented to the Tumor Board, and as before there isn't much clarity as to what the "white spot" might be. He still thinks it's likely nothing, and even the head of the radiology lab joked that he shouldn't even be allowed to present this tiny spot to the board. But they did all agree that it should be monitored.
An aggressive approach would be to have an MRI in a week or two. To me that seems less useful, since if it's still there and the same, we don't learn anything. Two weeks is not a lot of time to grow. For me, the approach that makes the most sense is to wait a month and then get another MRI. At that point, any changes will become more clear and we'll know what it is and what to do about it. And a month isn't long enough for a tumor to take over my life. Speaking of which, I've got one more month to enjoy. So I'm off!