Impact of nasal septal deviation on olfactory bulb and olfactory tract morphometry

The olfactory bulb (OB) is the central processing structure of olfactory information, but the effect of nasal septal deviation (NSD) on olfactory system morphology remains unclear. This study aimed to evaluate the morphometric and volumetric changes in the OB and olfactory tract (OT) associated with the direction and angle of NSD, and to investigate the relationship between these changes and septal morphometric parameters.

This prospective autopsy study included 86 cases aged 18-80 years, classified by computed tomography (CT) as right NSD (n = 46) and left NSD (n = 40). OB and OT length, width, weight, and volume were measured, and normalized volume and weight ratios were calculated. NSD angle, septum volume, surface area, curved and straight lengths, and tortuosity ratio were assessed in three-dimensional (3D) Slicer. Cases were grouped into normal, mild, moderate, or severe categories.

Left OB length was shorter in left NSD (13.00 ± 4.36 mm vs. 14.89 ± 4.42 mm; p = 0.049). OB width was lower on the deviated side: right OB width was 5.23 ± 1.23 mm in right NSD, and left OB width was 4.96 ± 0.91 mm in left NSD (p = 0.008 and p < 0.001). Left OT length and width were lower in left NSD (20.86 ± 5.92 mm, p = 0.003; 4.00 ± 0.90 mm, p < 0.001). In both NSD groups, the deviated side showed significantly lower OB and OT morphometric, volumetric, and normalized volume measurements than the contralateral side (all p < 0.001). OB and OT widths and tortuosity ratio differed with severity (p < 0.05), and deviation angle correlated with tortuosity ratio in right NSD (r = 0.494, p < 0.001).

NSD is associated with side- and severity-related morphological variations in the OB and OT, providing new anatomical evidence of structural asymmetry within the olfactory pathway. Further studies combining imaging-based morphometry with psychophysical olfactory testing are needed to determine the functional and clinical relevance of these findings.