Diffusion tensor magnetic resonance imaging before and after release of visual pathway compression by pituitary tumors

INTRODUCTION: Visual impairment is a common clinical manifestation and surgical indication of pituitary adenoma due to the compression of the optic chiasm or nerve. Most lesions can be surgically decompressed through the transsphenoidal approach, which is recommended as the most rapid and reliable relief from the compression. The postoperative improvement of visual function may occur in a wide range of time from minutes to years. Diffusion tensor imaging (DTI), as a noninvasive magnetic resonance technique based on measuring the diffusion of water molecules in brain white matter, has been applied to optic evaluation of neuropathies such as glaucoma, optic neuritis, blindness and tumors. Moreover, interests in the reconstructions of the optic pathway based on DTI, including the optic nerve, optic tract and optic radiation, have been increasing. In the reconstructing process the fractional anisotropy (FA) value is essential to reflect the neural conductivity. In this study an intraoperative magnetic resonance imaging (MRI) scanner was utilized to evaluate the very early visual improvement after decompression of the optic chiasm. This is the first quantitative study of the inner structure of the visual pathway before and after chiasmal decompression using intraoperative diffusion tensor tractography. METHODS: 22 patients with pituitary tumors compressing the optic chaism underwent transsphenoidal decompression. Preoperative and intraoperative conventional MRI and diffusion tensor tractography were applied to evaluate the decompression as well as the extent of resection. A comparison of the FA value, the number of detectable fibers in the optic chiasm and the optic radiation was made between the preoperative compression status and the intraoperative decompression status. The relationship between DTI data and clinical parameters was studied. RESULTS: All pathways of the visual tract were successfully reconstructed. An increase occurred in the FA value at the optic chiasm in 20 of the 22 patients (91%) and in the number of detectable fibers in 21 (95%) patients during the decompression. The overall mean FA value at the optic chiasm increased from 0.276 ± 0.049 to 0.303 ± 0.052 (P<0.01) and an increase in the number of detectable fibers was observed from 12.4 ± 5.3 to 18.0 ± 5.0 (P