Clinical Implications of Septal Deviation in Lateralized Olfaction

OBJECTIVES Results of butanol threshold tests (BTTs) have shown that birhinal olfaction tends to converge toward monorhinal olfaction of the dominant nostril. However, birhinal olfaction may also be worse than dominant-side monorhinal olfaction. The goal of our study was to investigate the effect of deviated nasal septum on birhinal olfaction in patients with lateralized olfaction and to examine the effect of septoplasty in these patients. METHODS A retrospective study with planned data collection was conducted in 518 patients who underwent BTTs. Lateralized olfaction was defined as monorhinal BTT scores that differed by >2 between sides. Underestimated birhinal olfaction was defined as a birhinal BTT score >2 lower than the dominant nostril monorhinal BTT score. Patients with lateralized olfaction were divided into 2 groups: group 1, underestimated birhinal olfaction; and group 2, without underestimated birhinal olfaction. RESULTS Among 518 patients, 112 with lateralized olfaction were enrolled in this study. Group 1 included 23 patients (20.5%) and group 2 included 89 patients (79.5%). The severity of septal deviation (ratio of the distance of narrower side to wider side) did not differ between the 2 groups. Septal deviation to the dominant nostril was more common in group 1 than group 2 (73.9% vs. 37.6%; P=0.002). Five patients with septal deviation to the dominant nostril with underestimated birhinal olfaction underwent septoplasty. Improved lateralized olfaction occurred in all 5 patients postoperatively (P=0.041). CONCLUSION Septal deviation of the dominant nostril in patients with lateralized olfaction is associated with underestimated birhinal olfaction. Septoplasty may improve olfaction by increasing airflow in the dominant olfactory side.