Hi and welcome to our little MS community,
IF i am understanding what you've written, your primary care physician ordered your one and only brain MRI but he was looking for evidence of an unrelated condition (pituitary adenoma) and unexpectedly, you're now looking at the possibility of MS being the cause of your symptoms...
The MRI could of been just a standard brain MRI, and run without MS protocol because your PCP wasn't looking specifically for evidence of MS and it was probably done on the more common 1.5T strength MRI too. A 3T MRI, run with MS protocol, with and without contrast is usually recommended when MS is suspected.....basically a 3T will show up to 25% more than a 1.5T and MS protocol has 3mm slices instead of the standard 5mm, which all helps to show up more lesions (if there are more to find) and potentially find enough to meet the MS Mcdonald diagnostic criteria...
Your MRI still found some evidence suggestive enough to put MS high up on your potential causation list, location is very important when you haven't as yet been diagnosed. The MS Mcdonald diagnostic criteria mentions 4 specific locations (periventricular, infratentorial, juxtacortical, spinal cord) which you need lesions in at least 2 out of the 4 but it also mentions evidence of at least 2 attacks.....you've mentioned having some older established lesions and newly enhancing lesion(s), and you have 2 periventricular which is definitely one of the specified locations, but it is completely illogical to discount the right temporal lobe lesion when it enhanced with contrast which is what demyelinating lesions do!
The LP is no longer necessary, it's very useful when there isn't enough evidence on the MRI and clinical (abnormal neurological assessments) but again it's completely illogical to discount an LP that is suggestive/consistent with MS, when 2+ unique obands is what 80-90% of MSers actually have.
I honestly can't say if you already have enough diagnostic evidence or not, MS is diagnosed on the totality of your diagnostic evidence and whilst i understand that 3 months may seem like a long time to wait, but in general that's quick, it;s not uncommon to have 6 or 12monthly follow ups and diagnosis can unfortunately take years.
I would definitely recommend you double check on if the neurologist your seeing is an MS specialist or just a general neuro, and if he is only a general neurologist, then it would be in your best interest to seek the opinion of a neurologist who does specialise in MS!
Hope that helps.....JJ
ps if you have any questions please feel free to ask anything and we'll do our best :D