There is no single test that is diagnostic of MS, including MRI. The lesions 
detected with MRI are pathologically nonspecific. The principles of MS diagnosis 
are based on showing dissemination of white matter lesions in space and time. 
MRI is the most sensitive method for revealing asymptomatic dissemination of 
lesions in space and time. The pattern and evolution of MRI lesions, in the 
appropriate clinical setting, has made MRI abnormalities invaluable criteria for 
the early diagnosis of MS. The first important role for MRI in the diagnosis of 
MS allows for an early diagnosis of MS for CIS patients using the IP diagnostic 
criteria, including MRI for dissemination in space (DIS) and time (DIT). The 
sensitivity of diagnosing MS within the first year after a single attack is 94%, 
with a specificity of 83%. The MRI evidence required to support the diagnosis 
varies, depending on the strength of the clinical findings. Allowing a new MRI 
lesion to substitute for a clinical attack doubles the number of CIS patients 
who can be diagnosed as having MS within 1 year of symptom onset. Increasing the 
sensitivity of the test with more lenient criteria, as recommended by the AAN 
subcommittee, can result in decreased specificity. The second important role for 
MRI in the diagnostic work-up of suspected MS patients is to rule out 
alternative diagnoses obvious on MRI, such as spinal stenosis and most brain 
tumors. Characteristic lesions that favor MS include Dawson Fingers, ovoid 
lesions, corpus callosum lesions, and asymptomatic spinal cord lesions. However, 
other white matter diseases can have similar appearances on MRI. Persistent 
gadolinium enhancement greater than three months, lesions with mass effect, and 
meningeal enhancement suggest other disorders. A standardized MRI protocol for 
brain and spinal cord is crucial for comparing across studies or between 
centers. T2W MRI cannot distinguish between acute and chronic lesions. 
Gadolinium provides useful information about new lesion activity and is helpful 
in ruling out alternative diagnoses such as neoplasm, vascular malformations, 
and leptomeningeal disease. A single gadolinium-enhanced MRI can potentially 
provide evidence for dissemination in space and time. Spinal cord imaging is 
equally valuable to rule out spinal stenosis or tumor, and for detecting 
asymptomatic lesions when brain imaging is nondiagnostic in patients suspected 
of having MS. Precise criteria may be too suggestive that MS can be diagnosed by 
MRI and a negative MRI at the time of CIS does not rule out MS. MRI evidence 
plays a supportive role in what is ultimately a clinical diagnosis of MS, in the 
appropriate clinical situation, and always at the exclusion of alternative 
diagnoses.