Olfactory bulb volume and depth of olfactory sulcus in patients with idiopathic olfactory loss

Olfactory loss is considered as idiopathic (IOL) when no cause can be found, neither on the basis of a standardized history nor a thorough clinical evaluation. Olfactory bulb volume (OB) has been shown to be decreased in patients with olfactory loss due to trauma, infections, or sinonasal disease. However, OB volume has not yet been investigated in IOL patients. Twenty-two patients with IOL were compared with 22 controls in terms of olfactory performance and of OB volume assessed with magnetic resonance imaging (MRI). Psychophysical testing confirmed that patients had lower scores than controls: P < 0.001 for threshold (T), discrimination (D), identification (I) and global TDI score. Mean right, left and total OB volumes were significantly smaller for IOL patients as compared to controls. Both for IOL and controls, there was a significant correlation between odor thresholds and total OB volume, respectively. In conclusion, patients with IOL have decreased olfactory function and decreased OB volume when compared with controls. This was previously demonstrated for patients with postinfectious or post-traumatic olfactory dysfunction, but not for patients with uneventful conditions possibly damaging their olfactory apparatus.