DTI is a new MRI technology which may give data on the compressed tissue’s microstructural properties. This study assessed if DTI can accurately evaluate optic pathway in patients with suprasellar masses. DTI is based on the anisotropic properties of water molecule motion in white matter fiber. The motion of water molecules with the axis of the fiber is relatively free, while it is more limited if it is perpendicular to it. Accordingly, this technique can track the fibers on a pixel by pixel base and can measure the anisotropic properties by parameters as fraction anisotropy (FA). DTI is a non-invasive technique that detects structural changes. Although there is plethora of reports on DTI in brain disorders, there are only few studies which detect changes in white matter structure. Barker’s group (Wieshmann  and Eriksson ) was the first to find that DTI may detect precisely displacements in the white matter fibers and found that the compression of white matter fibers leads to increase in anisotropy.
Another study by Witwer et al. used directionally color-coded maps or directionally encoded color (DEC) mapping of DTI to track white matter displacement. Also, Assaf et al.  have found that DTI parameters can help tracking white matter displacement in 2D DEC-FA maps.
Compression by a mass causes structural changes as loss of the myelin sheath, axonal degeneration, cell or neuronal degeneration, and gliosis. White matter compression by a tumor leads to increase in FA values, and another cause of the DTI measures change may be the edema like changes which leads to distension of Virchow-Robin spaces adjacent to the optic tract .
Group of reports studied the MRI findings of the optic pathways in multiple diseases. Tokumaru et al.  found that hyperintense signal of the optic chiasma due to the pituitary macroadenoma was associated with visual acuity impairment.
The change of the DTI measures of optic pathway, due to compression by masses lesions, may be a good prognostic factor of the visual function. DTI measures as the FA, AD, and RD may show structural criteria as the degree of myelination and axonal density. These measures give data about the white matter microstructure that cannot be evaluated by conventional MRI. Anik et al.  reported that if after endoscopic pituitary surgery, the mean FA value is reduced and the mean diffusivity value is elevated of the optic pathway, it is an indicator of there is no improvement.
This study hypothesized that the suprasellar masses compressing the optic pathway cause changes in the DTI parameters values. The studied patients revealed that, on using DTI, when compared values in cases with suprasellar masses and control cases without masses, significant changes were found in the FA, AD, and ADC values. The FA values of the optic chiasma in cases group with mass compression increased compared to the control group. The AD and ADC values of the optic chiasma in cases group with suprasellar mass significantly decreased compared to the control group, and this study was in accordance to Yamada et al. In their study, optic chiasma of cases with compressive suprasellar masses showed significantly decrease in mean AD, ADC, and RD values compared to mean values of patients with no masses .
Yamada et al.  found in a study performed on 24 consecutive cases with intra or parasellar masses; they performed diffusion tensor magnetic resonance imaging of optic pathway for all the patients. They revealed that AD and RD values showed significant changes in cases with masses than those of patients without masses compression. Optic chiasma of cases with visual field defect showed significant decrease in AD and RD values more than patients without the visual field defect.
Schonberg et al.  were studying the characters of the displaced white matter by brain masses and evaluated the different diffusion tensor measures. They found that the RD decreased, while the AD increased, and that lead to an increase in the FA with no significant difference in the ADC. The mechanism of these changes is the increase in the fiber density and tension, and another mechanism might be increasing in the homogeneity of the fibers by a tighter alignment of the fibers within the fiber bundle.
This study was in accordance to Schonberg et al.  in the compressive mass effect on the optic chiasm revealed significant increase in FA value, but this study disagreed with them as it detected that on compression of optic chiasma, there were significant decrease in the AD and ADC values.
Singman et al.  were studying the indirect traumatic effect of optic neuropathy. The affected optic pathway revealed that mean FA value progressively decreased, and mean RD value progressively increased.
The DTI parameters of the control cases without suprasellar mass compressing the optic pathway revealed lower FA and higher AD, RD, and ADC values in comparison with other studies. There are a lot of factors explaining these differences as the partial volume effect of the surrounding CSF, the manual setting of ROIs position, signal to noise ratio, imaging orientations, spatial resolution, and CSF and fat suppression ratio .
In terms of the correlation between clinical, visual field assessment, and radiological findings, this study confirmed that there are significant changes in the DTI parameters in patients with visual field disorder, which makes DTI a crucial and essential tool in the evaluation of patients with suprasellar masses. DTI will provide the clinicians with accurate numbers that reveal to which degree the optic pathway is affected. For this reason, DTI is highly recommended when performing MRI for suprasellar masses.
Regarding our present study limitations, there are two limitations. The first one, and the main drawback in DTI analysis, is the length of the acquisition time as the duration of the examination is 6 min 26 s, and the second one is related to the ROIs’ size, which were small and may have included contamination from the surrounding structures.