Specific Imaging Findings

MR is the imaging method of choice and shows multiple small foci of high T2 signal intensity throughout the white and gray matter, supra- and infra-tentorially. Corpus callosum is always involved. Involvement of gray matter is more apparent within the basal ganglia and thalami but also occurs in the cortex. Many lesions enhance after contrast administration during the acute and subacute periods of the disease. Leptomeningeal contrast enhancement may also be seen and as the CSF has increased proteins its signal intensity on FLAIR images may be increased. During the acute period lesions tend to show reduced ADC. A pathognomonic finding for Susac syndrome is that of rounded lesions centrally within the corpus callosum (and not at the calloso-septal interface as in multiple sclerosis). Another typical finding is “string of pearls” – the studding of the internal capsules with microinfarcts on MRI. In the chronic stage the white matter lesions may become confluent and the brain suffers generalized atrophy.

Pertinent Clinical Information

The classic clinical triad includes: subacute encephalopathy, retinal artery branch occlusions and sensorineural hearing loss. Most patients are women between 20 and 40 years of age. Findings on brain MRI, audiogram, and funduscopy help reach the correct diagnosis. Unfortunately, the complete clinical triad is present in less than 5% of patients at the onset of the disease. Headache routinely accompanies the encephalopathy and may be constant, migrainous, or both. Bilateral long-tract signs commonly accompany the encephalopathy, which is laden with psychiatric features, confusion, memory loss, and other cognitive changes. It has been proposed that the diagnosis of Susac syndrome can be made when only the encephalopathy and pathognomonic MRI lesions are present.