Cortical Atrophy, White Matter Lesions, and Bulb Configuration in Patients with Idiopathic Olfactory Loss and Other Causes of Olfactory Loss

Abstract

Introduction: While magnetic resonance imaging (MRI) is not included in the current guidelines for diagnosing olfactory disorders in the most recent position paper on olfactory dysfunction, both 1.5T and 3T MRI are commonly used in the diagnostic workup of many patients with olfactory loss. Often, MRI is used to rule out intracranial tumours, but other useful information may be obtained from MRI scans in these patients. The potential of MRI in olfactory loss depends on sufficient knowledge of structural changes in different aetiologies of olfactory loss. We present common clinical MRI findings in olfactory loss and evaluate the usefulness of structural integrity scores in differentiating between aetiologies. Methods: In this study, we investigated if white matter hyperintensities (WMHs, measured by Fazekas score), global cortical atrophy (GCA), and medial temporal lobe atrophy (MTA) are more common in patients with idiopathic olfactory loss than in patients with acquired olfactory loss due to other aetiologies. Furthermore, we compared olfactory bulb (OB) configurations in different olfactory loss aetiologies. Results: In 88 patients with olfactory loss, WMHs, GCA, and MTA were not more significant findings on MRI in idiopathic olfactory loss (n = 51) compared with other causes of acquired olfactory loss (Fazekas score p = 0.2977; GCA score p = 0.6748; MTA score p = 0.7851). Bulb configurations differed in patients suffering from post-traumatic olfactory loss and may aid in identifying the underlying aetiology in patients where trauma is among the suspected causes of olfactory loss. Conclusion: We recommend that structural MRI with an OB sequence is included in the diagnostic evaluation of olfactory loss with suspected congenital and post-traumatic aetiology and should be considered in idiopathic olfactory loss with suspected central aetiology (e.g., tumour).