Correlation of olfactory function with changes in the volume of the human olfactory bulb.

OBJECTIVE: To investigate changes of olfactory bulb (OB) volume over time in relation to olfactory function. DESIGN: Prospective, before-after trial. SETTING: Outpatient clinic of a university clinic for otorhinolaryngology. PATIENTS: A total of 20 patients with olfactory loss participated in the study. The duration of olfactory deficits ranged from 3 months to 6 years. MAIN OUTCOME MEASURES: Olfactory function was assessed for phenyl ethyl alcohol odor threshold, odor discrimination, and odor identification. Olfactory bulb volume was determined using magnetic resonance imaging. RESULTS: In initially hyposmic patients (n = 13), changes in OB volume were found to correlate with odor threshold changes (r = 0.82; P = .001); no such correlation was found for odor discrimination or odor identification. CONCLUSION: As demonstrated in a longitudinal study for the first time to our knowledge, the human OB is a highly plastic structure that responds to individual changes in olfactory status.

Reduced olfactory bulb volume in post-traumatic and post-infectious olfactory dysfunction.

The olfactory bulb is a highly plastic structure the volume of which partly reflects the degree of afferent neural activity. In this study, 22 patients with post-infectious olfactory deficit, nine participants with post-traumatic olfactory deficit, and 17 healthy controls underwent magnetic resonance volumetry of the olfactory bulb. Patients presented with significantly smaller olfactory bulb volumes than controls; significant correlations between olfactory function and bulb volume were observed. Patients with parosmia exhibited smaller olfactory bulb volumes than those without parosmia. Findings indicate that smell deficits leading to a reduced sensory input to the olfactory bulb result in structural changes at the level of the bulb. Reduced olfactory bulb volumes may also be considered to be characteristic of parosmia.