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What is Radiologically isolated syndrome and explain in detail?
Radiologically isolated syndrome (RIS) is a clinical situation in which a person has white matter lesions suggestive of multiple sclerosis (MS), as shown on an MRI scan that was done for reasons unrelated to MS symptoms. The nerve lesions in these people show dissemination in space with an otherwise normal neurological examination and without historical accounts of typical MS symptoms.MRI findings that are consistent with multiple sclerosis have been observed in healthy people who underwent MRI scanning, and 50% go on to develop symptomatic MS, sometimes with a primary progressive course.  This condition was first characterized in 2009.

Diagnosis
The criteria for an RIS diagnosis are as follows:
The presence of incidental MRI findings in the CNS white matter:
Ovoid and well-circumscribed homogeneous foci, with or without involvement of the corpus callosum
T2 hyperintensities larger than 3 mm in diameter, which fulfill at least 3 of the 4 Barkhof MRI criteria for DIS
The CNS abnormalities are not consistent with a vascular condition
No historical accounts of clinical symptoms consistent with neurological dysfunction.
MRI anomalies do not account for apparent impairment in social, occupational, or generalized areas of functioning.
MRI anomalies are not due to substance abuse, such as recreational drug use, toxic exposure, or a prior known medical condition.
Exclusion of a differential diagnosis of leukoaraiosis, or extensive white matter pathology excluding the corpus callosum.
MRI anomalies of the CNS are not accounted for by another disease.

Discovery
RIS is discovered when an MRI scan is performed for other reasons.  The most common symptom that led to the incidental discovery of RIS is headache.  Other common reasons are trauma, psychiatric disorders, and endocrinological disorders.

Management
Currently, routine clinical follow-up and MRI neuroimaging surveillance is the standard by which patients are observed. While treatment of MS disease modifying therapies have been given to some individuals with RIS, the majority opt for active surveillance and the appearance of clinical symptoms before commencing treatment, as treatment is considered controversial.

Prognosis
In a 5 year study, clinical events, which refers to the first symptoms of exacerbations, clinical attacks, flare ups, or severe symptoms, indicative of MS, appeared in 34% of individuals. Of those who developed symptoms, 9.6% fulfilled criteria for primary progressive multiple sclerosis (PPMS).

Epidemiology
Due to the incidental nature of RIS, exact figures on prevalence is unknown, though it has been suggested that RIS is the most common type of asymptomatic MS. The prevalence may be higher in relatives of patients with MS