Improvement of olfactory function after sinus surgery correlates with white matter properties measured by diffusion tensor imaging.

Impaired olfaction is associated with a volume decrease in the olfactory bulb as well as in the gray matter of cortical olfactory areas. On the other hand, restitution of an impaired olfaction results in a regain of volume in these regions. Studies investigating similar changes in the cerebral white matter are virtually not existent. The aim of this prospective study therefore was to investigate cerebral white matter using magnetic resonance diffusion tensor imaging (DTI). 31 patients (54±13years) with olfactory impairment (chronic rhinosinusitis) and planned functional endoscopic sinus surgery (FESS) were included. Magnetic resonance imaging (MRI) data sets were acquired pre-operatively and 3months after surgery. Pre- and postoperative olfactory testing was performed to assess the olfactory threshold, discrimination, and identification (TDI) score. A significant postoperative TDI improvement by 9.06±8.81 points was observed. Two groups were subsequently formed - one with relevant postoperative olfactory gain (ΔTDI≥10 points, 12 patients) and one without gain (ΔTDI<10 points, 19 patients). DTI parameter showed a significant correlation with the TDI score in the left anterior cingulate cortex and the right amygdala. In the group with relevant olfactory improvement higher values of fractional anisotropy and apparent diffusion coefficient were found in the right parahippocampal area and in the white matter below the left inferior temporal sulcus. Tract-specific diffusion property analysis revealed significant group differences in the cingulate cortex in spatial relationship to the perisplenial cortex. Overall, this prospective study indicates structural changes in white matter after postoperative restoration of olfaction.