MR Imaging-Based Evaluations of Olfactory Bulb Atrophy in Patients with Olfactory Dysfunction

Abstract

Background and purpose: Although the olfactory bulb volume as assessed with MR imaging is known to reflect olfactory function, it is not always measured during olfactory pathway assessments in clinical settings. We aimed to evaluate the utility of visual olfactory bulb atrophy and neuropathy analyses using MR imaging in patients with olfactory dysfunction.

Materials and methods: Thirty-four patients who presented with subjective olfactory loss between March 2016 and February 2017 were included. Patients underwent a nasal endoscopic examination, olfactory testing with the Korean Version of the Sniffin' Sticks test, and MR imaging. All patients completed the Sino-Nasal Outcome Test and Questionnaire of Olfactory Disorders. Olfactory bulb atrophy and neuropathy were evaluated on MR images by 2 head and neck radiologists.

Results: The etiology of olfactory loss was chronic rhinosinusitis with/without nasal polyps in 15 (44.1%) patients, respiratory viral infection in 7 (20.6%), trauma in 2 (5.9%), and idiopathic in 10 (29.4%) patients. Although 10 (29.4%) of the 34 patients were normosmic according to the Sniffin' Sticks test, their scores on the other tests were like those of patients who were hyposmic/anosmic according to the Sniffin' Sticks test. However, the detection rate of olfactory bulb atrophy was significantly higher in patients with hyposmia/anosmia than it was in patients with normosmia (P = .002). No difference in olfactory bulb neuropathy was identified among patients with normosmia and hyposmia/anosmia (P = .395).

Conclusions: MR imaging evaluations of olfactory bulb atrophy can be used to objectively diagnose olfactory dysfunction in patients with subjective olfactory loss.

Fig 1.

Atrophy of the olfactory bulbs. Compared with a patient with normal olfactory bulbs (A), which have an oval or inverted-J shape, patients with atrophy in the olfactory bulbs show asymmetric decreases in the size of the affected olfactory bulbs (B, right; and C, left, arrow) or flattening of the olfactory bulbs (D, arrows).

Fig 2.

Neuropathy of the olfactory bulbs. Homogeneous signal intensity in both olfactory bulbs is noted in a patent without neuropathy (A); however, focal (B) or diffuse (C) hyperintense areas in left olfactory bulb (arrow) compared with the white matter of the frontal lobe are visible on FLAIR images in patients with neuropathy.