Hi,
The suggestion to look in our Health Pages is a good one. There are several pages dealing with lesions and one about steroids among the others.
Avery quick synopsis is "active" or new lesion will only show up as enhancing the first 30-45 days of their formation. If the lesion is there it is already active since the lesions indicate areas of demylenation.
Also, lesions do not "match" up with symptoms. Sometimes the lesions are not visible as yet on the MRI.
Steroids are given when the symptoms flare up and are causing too much loss of function or bring a quicker resolution to symptoms as in optic neuritis. Steroids do not change the course of the disease they simply calm down the symptoms.
Hope this a better clarification for you. The best clarification can be found in the Health Pages:
http://www.medhelp.org/health_pages/Multiple-Sclerosis/Lesions-vs-Symptoms/show/61?cid=36
http://www.medhelp.org/health_pages/Multiple-Sclerosis/How-MRIs-Show-Lesions-in-MS/show/23?cid=36
Click on these links for the best info.
Ren