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Etemadifar et al. Imaging of demyelinated corpus callosum

is one of the common sites of brain involved in MS of recent studies showed increased ADC and reduced
patients. In MS, we can observe characteristic FA in both pathologic and NAWM. [29-33] Sigal et al.
[11]
macroscopic changes in conventional MRI, including: used DTI to investigate CC integrity in MS patients
(1) CC atrophy; (2) MS plaques; (3) signal changes and age matched controls. In agreement with other
within callososeptal interface. MS plaques mostly studies, [15,26,28,31] MS patients had significant reduction
[6]
occur in the body of the CC, as suggested by some in CC ’s FA compared with control group in all sub-
studies. [21-25] Diffuse atrophy of the CC is believed to region of CC, indicating axonal loss and dysfunction in
be a part of general cerebral atrophy in long standing callosal fibers. Most recent studies agree on the fact
cases or it can be caused by wallerian degeneration that in MS patients all MRI indices and parameters are
and loss of axons within the CC. According to the altered pathologically especially in the CC structure.
[26]
[34]
study by Chen et al., MRI findings can have a big role In the study by Farber et al. ADC was found to be
[6]
[35]
in discrimination between MS and other demyelinating helpful as a great parameter for differentiation between
disorders, in particular MS and Neuromyelitis optica. MS and other demyelinating diseases, as ADC was
In this study in which sagittal T2 flair images with found to be significantly elevated in CC in MS patients
2 mm thickness were obtained from 23 patients with compared to control group and patients with ADEM
neuromyelitis optica (NMO), 42 patients with MS and disease. A study by Ozturk et al. showed all MRI
[13]
[35]
27 controls, results showed that subcallosal dash- indices were diffusely abnormal in the CC. In this
dot sign was much more common in opticospinal MS study both FA and magnetization transfer ratio (MTR)
patients than NMO. Contrary to the subcallosal dash- were decreased and mean and directional diffusivity
dot sign, subcallosal striations had no meaningful were increased, but it is to be said that MTR and FA
difference between MS and other two groups. had greatest difference between disease and control
[6]
According to some studies, MS lesions of CC found to group. By spatially tract profile analysis they localized
be small, at the lower border of CC next to the septum the most abnormal segments in the body and isthmus,
pellucidum and crossed the midline asymmetrically. with relative sparing of the rostrum and genu. [13]
On the other hand, ADEM causes individually large,
asymmetric lesions and involvements in marchiafava CC as a prognosis indicator
bignami disease were large, often symmetrically in the Quantitative MRI abnormalities in the CC partially
midline of the splenium and did not reach the edge account for cognitive and upper/lower extremity
of the CC. [5,27] Central CC volume along with medulla dysfunction in MS and ultimately the prognosis. Since
oblongata volume can help discriminate between cognitive disability is particularly difficult to measure
different subtypes of MS. Various subtypes of MS affect at bedside, and because cognitive and non-cognitive
different neuroanatomical regions of the CC differently. disability may proceed at different rates, the ability to
Most of the patients with secondary progressive MS associate cognitive impairment with imaging data may
had central CC with the volume of less than 55 mm, be useful for monitoring patients and assessment of
while patients with primary progressive MS had more response to therapy in clinical trials. Previous studies
CC volume centrally. [28] in MS have shown significant correlation between
cognitive status and CC microstructure. [11,36-38] There
Functional MRI has been also studies about the relationship
Although MRI is the gold standard imaging for between CC involvement’s patterns and prognosis
evaluation of MS brain lesions, more recent MR of MS. [7-11] Most of them showed that the damage to
techniques helped in exploring axonal loss, wallerian white matter network especially CC contributes to the
degeneration and microscopic changes in detail. DTI reduced processing speed in task specific abilities.
[39]
is promising technique for detecting structural changes A significant increase in CC’s MD was observed in
in MS lesions and revealing microscopic changes in relapsing remitting MS, even in benign form. [40-44]
NAWM and Normal appearing gray matter (NAGM). Moreover, patterns of tract FA reduction for cognitive
Using water diffusion as a basis to construct anatomic test, including localization of lesions in the body and
details, DTI offers the potential to identify structural splenium of the CC, only partially overlapped with T2
and functional adaptations before gross anatomical lesions, supporting that NAWM abnormality contributes
changes. Most important DTI parameters are Mean to cognitive dysfunction. In the study by Rimkus et al.
[45]
diffusion (MD) and FA. There are also some other results showed correlation between mean diffusion and
parameters in the matter of directional diffusivity such radial diffusivity, and expended disability status scale
as: radial and axial diffusivity, which have been used (EDSS), suggesting possible relationship between
by many recent studies. [15,25,26,28] Such parameters callosal demyelination and sensory motor dysfunction.
interestingly found to be helpful in detecting microscopic The cognitive dysfunction was concomitant with DTI
and structural changes in lesional and NAWM. Most changes in CC. MS group of patients showed decreased
Neuroimmunology and Neuroinflammation ¦ Volume 4 ¦ April 27, 2017 71