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Etemadifar et al. Imaging of demyelinated corpus callosum

FA and increased MD compared to the matched control deposition; (3) complement activation and some
group, which can be interpreted as loss of complexity other mechanisms yet to be investigated in further
in the white matter tracts in the initial pathological studies. [48,49] This changes lead to an alteration of the
process. As a conclusion, the microstructural changes blood brain barrier, which becomes visible by contrast
of CC can be helpful in determination of prognosis enhancement in CT and MRI. Increasing T1 and T2
in MS patients. They also found that macroscopic times are also observed and many studies agree on
changes of CC had no direct association with cognitive the fact that contrast enhancement are dominantly
dysfunction in such patients. There were also some present in acute phase of the disease and fade out as
[45]
studies like study by Natarajan et al. in which they the acute stage is passed. These studies also showed
[46]
found that the most abnormal DTI indices were present that the probable underlying causes for hyper intense
in secondary progressive MS patients. According lesions of brain and spinal cord may be edema and
to a longitudinal cohort study in 2012 CC atrophy of demyelination. [48,50,51] The most important common
6 months could predict clinically definite MS within features of white matter involvement is symmetric
2 years. It showed that faster decrease in CC cross periventricular and callosal hyper intense lesions on
sectional area and higher T2 lesion volume indicated a T2 weighted and flair images as a result of edema and
poorer prognosis. DTI directional diffusivity may offer demyelination. As a common finding, many studies
[35]
the potential to monitor therapeutic options and further showed that most of the ADEM patients (78%) have
understanding of the disease process and prognosis. absolute or relative periventricular sparing which was
In a DTI study looking at longitudinal changes in found to be a typical characteristic of ADEM in MRI.
brain tissues in a group of patients with MS receiving Some studies suggested that MRI involvement of CC
Natalizumab therapy, the authors found increased in ADEM patients can be multiple or single, especially
FA, decreased radial diffusivity and no change in in the splenium of the CC. They also showed that all
axial diffusivity in gadolinium enhancing lesions over callosal lesions can be enhanced or not, in MRI (with
the course of therapy. On the other hand, in normal Gd). Generally, the greatest difference between MS
appearing brain tissue, CC’s FA and axial diffusivity and ADEM is that, the likelihood of CC involvement
demonstrated further decline over time, while no in MS is far more common than ADEM (~60% vs.
significant change in radial diffusivity was observed. ~15%). [5,52]
[47]
Hence, the decline in axial diffusivity may suggest
involvement of axonal loss and degeneration in normal Functional MRI
appearing brain tissue at the early stage before ADEM predominantly affects white matter. It was
active lesions develop, possibly attributing to poorer reported that functional MRI parameters (axial
prognosis and progressive disability often observed and radial diffusivity) can estimate the extent of
in MS patients despite treatment. Many recent studies myelin injury in the CNS white matter. Although first
agree on the fact that longitudinal changes are most studies on patients of ADEM showed elevated ADC
rapid in CC area of the brain in MS disorder in different and reduced FA, Further exploration of directional
types of imaging. [16,19,35,43] diffusivity revealed unchanged axial diffusivity and
markedly increased radial diffusivity, suggestive of
CC IN ACUTE DISSEMINATED demyelination. These findings were consistent with
ENCEPHALOMYELITIS findings of study by Petzold et al., which showed
[53]
patients of ADEM having elevated ADC in sub-acute
MRI phase and reduced ADC in acute phase. Many other
Acute disseminated encephalomyelitis is an studies agree on this DTI changes in patients with ADEM
uncommon immune mediated inflammatory disorder. Tillema et al. did a retrospective DTI study
[5]
demyelinating disease of the CNS. It is usually a looking at non-lesional white matter changes within
monophasic illness, which may occur after vaccination, central fibers of the CC’s genu and internal capsule in
viral infection, in association with rheumatic fever, pediatric MS and ADEM. They found lower FA values,
or with unrecognized antecedent disorder. The increased radial diffusivity and no difference in axial
clinical picture is widespread CNS disturbance, diffusivity in patients with ADEM while in patients with
including: drowsiness, coma, multifocal neurological MS results were significantly different (decreased FA
signs and seizure due to involvement of the brain, and increased radial diffusivity). [5]
spinal cord and optic nerves. Radiologic findings of
ADEM are usually not pathognomonic. As a result, CC as a prognosis indicator
the differentiation of diagnosis is always difficult. Patients with ADEM are usually presented with variable
Pathologic findings of ADEM are usually due to: (1) neurologic signs especially after an infectious episode.
vascular damage; (2) circulating immune complex MRI is the technique of choice to show these lesions
72 Neuroimmunology and Neuroinflammation ¦ Volume 4 ¦ April 27, 2017