The diagnostic criteria for MS are dissemination in time and dissemination in space. Dissemination in time means that you need to have had at least two attacks (or one attack and a new lesion visible on MRI since then). Dissemination in space means that there have been at least two parts of your nervous system affected. If you have an MRI, then you need to have at least one lesion in two places typical of MS in order to satisfy the dissemination in space criterion. The typical places are: juxtacortical (touching the gray matter, the outside layers of the brain), periventricular (touching the ventricles, the "lakes" of fluid in the middle of the brain), infratentorial (in the brain stem or the cerebellum) and the spinal cord.
So, at the moment, your MRI isn't meeting the dissemination in space criterion. If your neuro sticks to the MRI criteria, the best he could diagnose you with is "probable MS". However, if your symptoms and clinical exam results support the presence of a lesion somewhere else, then he could diagnose MS (assuming you've had more than one attack).
If you google Polman et al (2011) Diagnostic Criteria for Multiple Sclerosis: 2010 Revisions to the McDonald Criteria you can download the full details.