Olfactory bulb volume in the clinical assessment of olfactory dysfunction.

The olfactory bulb collects the sensory afferents of the olfactory receptor cells located in the olfactory neuroepithelium. The olfactory bulb ends with the olfactory tract and is closely related to the olfactory sulcus of the frontal lobe. Many studies demonstrated that olfactory bulb volume assessed with magnetic resonance imaging is related to the olfactory function both in normal and pathological conditions. It has been shown that olfactory bulb volume changes with the degree of olfactory dysfunction, that it decreases with the duration of the olfactory loss and that patients with qualitative disorder such as parosmia have smaller olfactory bulbs than patients without parosmia. In this review, we will discuss the actual knowledge regarding olfactory bulb function, practical ways to measure olfactory bulb volume and olfactory sulcus depth, and report systematic observations regarding these measurements related to various causes of olfactory dysfunction, e.g. infection of the upper respiratory tract, head trauma, or neurodegenerative disease. Measurement of olfactory bulb volume may provide valuable information for patients with olfactory dysfunction.