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Etemadifar et al. Imaging of demyelinated corpus callosum

lower average MDs in medulla oblongata, internal involvement of genu of the CC can be useful to predict
capsule and thalamus. [64] the outcome of the disorder. The more decrease in FA,
the more complication is expected in the course of the
CC IN SUSAC SYNDROME disease. There were also some evidences showing
that serial DTI parameters can play a role in prediction
MRI of outcome and prognosis of the disease but, there are
Susac’s syndrome (SS) is a clinical triad of many aspects to be studied and explored yet in this
encephalopathy, branch retinal artery occlusion field of research. [60,63,70-72]
and sensorineural hearing loss. It is sometimes
misdiagnosed because of similarities with ADEM and OTHER DEMYELINATING DISORDERS
MS. Typical triad is not commonly seen. Brain is
[65]
the main target organ for SS, which makes MRI the Marchiafava bignami
best diagnostic test. Susac syndrome mostly causes MBD disease is a rare form of toxic demyelination of CC
micro-infarction in both gray and white matter. This associated with chronic alcohol consumption. Several
can cause hyperintense lesions at any area of the MRI findings have shown lesions not only in the CC but
brain, including CC. Micro-infarctions in SS have also in the hemispheric white matter. General pattern of
two specific patterns on MRI: “snowball lesions”, in CC pathology in MBD is hyperintensity on flair imaging
central parts of CC, and “string of pearls”, which is and sometimes hemispheric white matter, reflecting
commonly seen in internal capsule. [22,66] Raets et al. damage to myelin and vasogenic edema of the CC and
[67]
showed that the combination of typical central callosal extracallosal projections. Because of pathological
[27]
lesions with string of pearls is pathognomonic for SS. variety of this disorder there is no certain sequence
Encephalopathic SS always involves CC. Snow ball and pattern of pathology of CC in MBD. Some studies
lesions evolve to central callosal holes in the course showed that involvement of the CC in MBD was initially
of the disease. A pathognomonic change in post- in the genu, without significant association with DTI
encephalopathic phase of SS disease is linear defects changes of CC and NAWM. Afterward, there would
in central part of CC called “smokes”. As reported, be some changes in the splenium of CC. The most
[73]
[67]
CC involvement plays a critical role in early diagnosis probable reason why DTI changes were not associated
of SS and demands aggressive therapy. In severely with initial changes in the genu of CC is that the changes
affected patients, atrophy of cerebellum is usually seen were mostly due to vasogenic edema and that the
during sub-acute and chronic phase. Correspondent to lesion then converted into cytotoxic edema process.
what stated previously, Mateen et al. demonstrated Serial MRI and DTI method of evaluation in MBD
[68]
a series of cases of SS with 79% involvement rate of cases have been found to be significantly helpful and
CC. CC can be of significant help to distinguish SS that’s why there will be a great need for further studies
from other demyelination disorders of CNS. They on this method of evaluation for such demyelinating
showed CC involvement in SS is typically in the central disorders. It suffices to briefly review MBD data
[27]
part of the CC. because there is still significant potential for further new
neuroimaging methods for such a rare disease and our
Functional MRI main goal in this review is demyelinating diseases with
Kleffner et al. showed the most specific finding of autoimmune nature rather than the disorders caused
[69]
DTI in SS patients, was 25% reduction of FA in genu by environmental factors.
of Corpus callosum.Reduced fractional anisotropy in
the prefrontal areas of the brain was also observed; Infectious demyelinating disorders
while in MS patients, it was mainly seen in the body, Many CNS disorders can cause secondary
rostrum and splenium of CC. DTI is considered a demyelination as an early or late complication. One
useful method to detect microstructural damage based major category of CNS diseases, are infective ones.
on FA. FA reflects the spatial directionality of water To show the importance of CC in CNS involvement
[69]
diffusion, which is decreased in white matter damage; of such disease, a brief review is presented. Infective
contrary to normal diffusion in conventional MRI of CC demyelinating diseases, such as subacute sclerosing
and prefrontal area. This puts more emphasis on how panencephalitis (SSPE), streptococcus meningitis,
essential are new methods of Imaging in neuroimaging Lyme disease, etc. can involve CC with various
exploration of CC disorders. patterns. For instance, in SSPE lesions are mostly
asymmetric, bilateral and T2-hyperintense and involve
CC as a prognosis indicator the temporal and parietal lobes in the acute stage.
In spite of lack of knowledge on this specific subject, No specific pattern of involvement regarding the
some studies pointed out that FA reduction and CC is reported to date, although some case reports
74 Neuroimmunology and Neuroinflammation ¦ Volume 4 ¦ April 27, 2017