Functional septorhinoplasty alters brain structure and function: Neuroanatomical correlates of olfactory dysfunction

Abstract

Introduction: We previously demonstrated functionally significant structural plasticity within the central olfactory networks, in association with improved olfaction after surgical treatment of chronic rhinosinusitis (CRS). In order to confirm and expand on these findings, the primary aim of this study was to determine whether these same regions undergo functionally significant structural plasticity following functional septorhinoplasty (fSRP), in patients with non-CRS olfactory dysfunction (OD) of mixed cause. fSRP has previously been shown to improve olfactory function, and the secondary aim of this study was to provide initial insights into the mechanism by which fSRP affects olfaction.

Methods: We performed a pilot prospective, multimodal neuroimaging study in 20 participants undergoing fSRP, including patients with non-CRS OD of mixed cause, as well as normosmic surgical controls. Participants underwent psychophysical olfactory testing, assessment of nasal airway, structural and functional neuroimaging. This was performed pre- and postoperatively in patients, and preoperatively in controls.

Results: There was a statistically and clinically significant improvement in mean psychophysical olfactory scores after surgery. This was associated with structural and functional plasticity within areas of the central olfactory network (anterior cingulate, orbitofrontal cortex, insula, temporal pole). Improved psychophysical scores were significantly correlated with change in bilateral measures of nasal airflow, not measures of airflow symmetry, suggesting that improved overall airflow was more important than correction of septal deviation.

Conclusion: This work highlights the importance of these neuroanatomical regions as potential structural correlates of olfactory function and dysfunction. Our results also provide initial insight into the mechanistic effects of fSRP on olfaction. Further work could investigate the utility of these regions as personalised biomarkers of OD, as well as the role of fSRP in treating OD.

Keywords: cortical thickness; functional MRI; grey matter volume; olfaction; olfactory dysfunction; plasticity; septorhinoplasty; treatment.

Figure 1

Experimental paradigm.

Figure 2

Diagram showing: (A) standardised placement of spreader grafts between septum and upper lateral cartilage; (B) standardised placement of columellar strut between medial crura of lower lateral cartilage. ULC, upper lateral cartilage; LLC, lower lateral cartilage.

Figure 3

fMRI experimental paradigm.

Figure 4

Significant positive correlation between change in PNIF and change in T score after surgery, r = 0.68, P = 0.04.

Figure 5

Neuroimaging results. To help differentiate between imaging modalities, VBM results are shown using the ch2bet stripped skull brain template and fMRI results are shown using the avg152T1 brain template. All coordinates are in MNI space. Colour bars show associated peak T score (please note that the maximum integer labelled may not reach top of colour bar range). Left: patients vs. controls (visit 1): Structural and functional MRI results for patients (visit 1) vs. controls. For ease of display—axial sections only shown for OFC results and coronal sections only shown for results within the insula. Subsections: (a) VBM results for increased GM volume within the ACC of patients compared with controls (P < 0.00625); (b) fMRI results for increased BOLD signal with the ACC of controls compared with patients (P < 0.00625, ≥10 voxels); (c–e) VBM results for increased GM volume in patients compared with controls, within the TP, insula and OFC (P < 0.00625). Right: Patients pre- vs. postoperative (visit 1 vs. 2): Structural and functional MRI results for decrease in GM volume and increase in BOLD signal after surgery, in the patient group. For ease of display—axial sections only shown for OFC results and coronal sections only shown for VBM results within the insula and TP. Subsections: (a) VBM results for decreased GM volume within the ACC of patients after surgery (P < 0.00625); (b) fMRI results for increased BOLD signal within the ACC of patients after surgery (P < 0.00625, ≥10 voxels); (c–h) VBM results for decreased GM volume and fMRI results for increased BOLD signal within the insula, OFC and TP of patients after surgery.