gms | German Medical Science

Objective: High resolution MRI Diffusion Tensor imaging (DTI) was shown to be clinically useful in cranial nerve compression syndromes like trigeminus neuralgia. Therefore it was tempting to investigate structural alterations in the optical pathway accordingly. In our prospective study we analyzed DTI for sellar and parasellar pathologies causing direct compression of the optic nerve or chiasm. Based on previously published methods for interpretation we investigated DTI in the context of clinical and radiological features in patients with optic nerve compression in order to predict functional deficits.

Method: Patients with clinical or radio-morphological optic nerve compression were included prospectively. High resolution (3.0 Tesla) MRI (3D T1 KM, T2 and CISS sequences) as well as DTI data (fractional anisotropy (FA) and mean diffusivity (MD)) were obtained preoperatively in the affected optic nerve, chiasma or unaffected contralateral optic nerve. Additionally, morphological fiber imaging was done by tractography studies. Ophthalmological and DTI findings were evaluated by the respective (blinded) expert.

Results: Thirteen patients with optic nerve compression by different pathologies (pituitary adenoma (n=6), meningioma (n=4), hemangiopericytoma (n=1), craniopharyngioma (n=1) and aneurysm (n=1)) were included. FA and MD values in n=26 optical nerves with n=91 regions of interest (ROI) containing n=4459 Voxels were analyzed. Nasal and temporal fiber tracts separately could be outlined by tractography studies. However, previously published data on absolute threshold FA/MD values could not be reproduced. At best, there was a tendency for higher FA-values in morphologically compressed optic nerves, eventually preceding functional deficits. In patients with severe deficits, absolute FA values were not reliable, whereas an intra-individually comparison to the unaffected nerve seemed more reasonable.

Conclusions: DTI imaging in patients with local compression of the optic pathway is feasible, but significance of absolute FA/MD values is difficult to interpret. The influence of neural fiber compression and interfering edema, as well as partial volume effects and crossing fibers at the level of the chiasm/tract hamper a straightforward evaluation and must be thoroughly considered in DTI analysis. Yet, DTI analysis seems to be a promising new method for the prediction of functional deficits in patients with sellar and parasellar lesions affecting the optic pathway.