Assessment of Optic Nerve Impairment in Patients with Neuromyelitis Optica by MR Diffusion Tensor Imaging

Fractional anisotropy helps to differentiate the optic nerve impairment between neuromyelitis optica spectrum disorders and multiple sclerosis

OBJECTIVES

To assess the characteristics of optic nerve impairment between neuromyelitis optica spectrum disorders (NMOSD) and multiple sclerosis (MS) patients by fractional anisotropy (FA).

METHODS

Thirty-one NMOSD patients, 25 MS patients, and 17 heathy controls (HC) who underwent optic nerve DTI were included. The optic nerves of the NMOSD and MS patients were divided into vision-impaired (VI) subgroups and normal-appearing (NA) subgroups according to visual status, respectively. FA values were measured in the anterior, middle, and posterior segments of each intraorbital optic nerve.

RESULTS

FA values in VI NMOSD were significantly decreased in the whole optic nerve, especially the posterior segment of the optic nerve (p < 0.001). FA values measured in the anterior and middle segments of the optic nerve in VI MS were significantly decreased as compared to those in the HC (p < 0.05). Between NMOSD and MS, FA values in the posterior segment of the optic nerve showed significant differences (VI NMOSD vs. VI MS, 0.458 ± 0.097 vs. 0.568 ± 0.098, p < 0.001; NA NMOSD vs. NA MS, 0.568 ± 0.098 vs. 0.600 ± 0.085, p = 0.041, respectively). The signal intensity ratio (SIR) in the posterior segment of the optic nerve was significantly increased in VI NMOSD as compared with VI MS (p = 0.002). The combination of SIR and FA for distinguishing VI NMOSD from VI MS resulted in sensitivity, specificity, and positive and negative predictive values of 86.49%, 80.00%, 88.9%, and 76.2%, respectively.

CONCLUSION

FA could quantify the characteristics of NMOSD- and MS-related optic nerve impairment. DTI was a simple and effective imaging tool to differentiate between the two.

KEY POINTS

• NMOSD-related optic nerve impairment is extensive, often greater than half of the optic nerve, with the most significant involvement of the posterior segment of the optic nerve. • MS-related optic nerve impairment is more limited than NMOSD, and anterior and middle optic nerve involvement is common. • Optic nerve DTI is a convenient and effective imaging tool that can help characterize NMOSD and MS.

Prediction of pituitary stalk position in pituitary adenomas by visualization of the hypothalamo-hypophyseal tract using diffusion tensor imaging tractography

The preservation of pituitary stalk during surgery is very important for neurosurgeons. Sometimes, it is hard to identify the pituitary stalk in the operation. The hypothalamo-hypophyseal tract (HHT) projects through the pituitary stalk to the posterior pituitary gland. If the HHT can be identified, the position of pituitary stalk will be visualized. The diffusion tensor imaging (DTI) fiber tracking technique has been widely used for the quantitative assessment of the white matter integrity and thus may be suitable for the evaluation of the HHT.DTI was used to track the HHT in 11 patients with pituitary adenoma, and the location of the tract was compared with the pituitary stalk of postoperative image in those patients.The fiber tracking and 3D visualization of the HHT were successfully carried out in all 11 patients. Comparison between the tract and pituitary stalk of postoperative magnetic resonance imaging (MRI) was carried out in 9 patients. The results revealed that the position of tract was consistent with the pituitary stalk of postoperative MRI image in 8 patients (88.9%). The properties of tract showed that the median number of tract was 5.18 ± 7.00, the median fractional anisotropy (FA) was 0.14 ± 0.04, and the median length was 28.81 ± 7.94 mm.HHT can be tracked and visualized with the DTI-FT technique. It will be helpful to identify the location of pituitary stalk preoperatively.

Diffusion tensor imaging for multilevel assessment of the visual pathway: possibilities for personalized outcome prediction in autoimmune disorders of the central nervous system

The afferent visual pathway represents the most frequently affected white matter pathway in multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD). Diffusion tensor imaging (DTI) can reveal microstructural or non-overt brain tissue damage and quantify pathological processes. DTI facilitates the reconstruction of major white matter fiber tracts allowing for the assessment of structure-function and damage-dysfunction relationships. In this review, we outline DTI studies investigating the afferent visual pathway in idiopathic optic neuritis (ON), NMOSD, and MS. Since MS damage patterns are believed to depend on multiple factors, i.e., ON (anterior visual pathway damage), inflammatory lesions (posterior visual pathway damage), and global diffuse inflammatory and neurodegenerative processes, comprehensive knowledge on different contributing factors using DTI in vivo may advance our understanding of MS disease pathology. Combination of DTI measures and visual outcome parameters yields the potential to improve routine clinical diagnostic procedures and may further the accuracy of individual prognosis with regard to visual function and personalized disease outcome. However, due to the inherent limitations of DTI acquisition and post-processing techniques and the so far heterogeneous and equivocal data of previous studies, evaluation of the true potential of DTI as a possible biomarker for afferent visual pathway dysfunction is still substantially limited. Further research efforts with larger longitudinal studies and standardized DTI acquisition and post-processing validation criteria are needed to overcome current DTI limitations. DTI evaluation at different levels of the visual pathway has the potential to provide markers for individual damage evaluation in the future. As an imaging biomarker, DTI may support individual outcome prediction during personalized treatment algorithms in MS and other neuroinflammatory diseases, hereby leveraging the concept of predictive, preventive, and personalized medicine in the field of clinical neuroimmunology.