Hi Sue, and welcome
Jon was a bit too kind about my expertise: MRI I’ll vouch for, B12 I’m really just a semi-informed novice Anyway, I can certainly help further with the MRI bit.
“Numerous T2 hyperintense lesions mainly within the subcortial white matter of both cerebal hemispheres although a couple are; periventriclar and juxtacortical in location (12 in total). I understand that the lesions have increased since I had an MRI 18 months ago.”
When they do MRI scans, they use different settings so that the different types of brain matter show up as different shades of gray - the higher the signal from an area, the paler the colour it is in the image. There are three main types of brain matter: gray matter (the stuff that does all the encoding, processing, storage, “thinking”), white matter (the stuff that connects all the bits of gray matter) and CSF (cerebrospinal fluid, which is a bit like the oil in an engine). In a T2 scan, gray matter looks pale gray, white matter looks darker gray and CSF looks white. Lesions (areas of damage) contain fluid so they also show up white (or at least paler than expected from the surrounding matter).
So, “numerous T2 hyperintense lesions” basically means lots of white spots on the T2 scans.
The outer layers of the brain are made up of gray matter. These are called the cortex. Under this is called subcortical. The matter lying just under the cortex is white matter. When you go further into the brain, the white matter starts being called “deep” white matter.
The brain has 3 main parts: the cerebrum (the big bit that everyone thinks of as the brain), the cerebellum (the separate, round part underneath the back end of the cerebrum) and the brain stem (the bit that joins the cerebrum and the spinal cord: basically the top of the spinal cord). The cerebrum has two halves: the hemispheres. So “mainly within the subcortial white matter of both cerebal hemispheres” means that most of your lesions are within the white matter lying under the cortex and in both halves of the big bit of the brain, the cerebrum.
Periventricular basically means next to the ventricles. The ventricles are the lakes of CSF lying in the middle of the cerebrum. It is a typical location of MS lesions.
Juxtacortical basically means right next to / into the cortex. It is another area that is typical of MS lesions.
So, you have 12 lesions which lie mainly in the white matter, but some are next to the ventricles and some are right next to the cortex. The fact that you have more lesions now than when you last had your scan means that whatever is causing these lesions has been active in that time.
Jon has mentioned the McDonald criteria. It is worth googling for these - they are free to download and explain exactly what is needed when diagnosing MS.
The basic criteria are dissemination in time and dissemination in space: in other words, more than one attack and more than one place affected. The MRI criteria for proving these are new lesions in a second scan and lesions in at least 2 of 4 areas of the central nervous system that MS tends to attack: periventricular, juxtacortical, infratentorial (basically the cerebellum and the brain stem) and the spinal cord.
From what you’ve said, your MRI results meet both these criteria, however, your B12 deficiency does confuse matters a bit because it can cause lesions and be very difficult to distinguish from MS. If your B12 levels have been normal since you had your first MRI, then I would think that it couldn’t be to blame for the new lesions at least, but I’m not 100% confident. I have also read that B12 lesions can resolve (disappear on the MRI) once levels are restored to normal, but again I’m not 100% confident. Anyway - the B12 deficiency is something that the neuro will have to try and factor out. There are also other things that can cause lesions so while it looks awfully like MS, it could still be something else.
Try to keep an open mind. One day at a time!