Impact of Nasal Septal Deviation on Olfactory Bulb and Olfactory Tract Morphometry

Background: 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 evaluated OB and olfactory tract (OT) morphometric and volumetric changes according to NSD direction and angle and their relationship with septal morphometry.Methods: This prospective autopsy study included 86 cases aged 18–80 years, classified by 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, septal volume, surface area, curved and straight lengths, and tortuosity ratio were assessed in 3D Slicer. Cases were grouped into normal, mild, moderate, or severe categories.Results: Left OB length was shorter in left NSD (13.00±4.36mm vs. 14.89±4.42mm; p=0.049). OB width was lower on the deviated side: right OB width was 5.23±1.23mm in right NSD, and left OB width was 4.96±0.91mm in left NSD (p=0.008 and p<0.001). Left OT length and width were lower in left NSD (20.86±5.92mm, p=0.003; 4.00±0.90mm, p<0.001). OB+OT volume was reduced on the deviated side (right NSD:0.14±0.03cm³, p=0.003; left NSD:0.13±0.03cm³, p=0.016), as were normalized volume ratios (0.13±0.02 and 0.12±0.03; 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).Conclusion: NSD direction and severity may cause lateral asymmetry in OB and OT morphology. Reduced OB/OT width and volume on the deviated side suggest that nasal airflow asymmetry may affect central olfactory structures.