Congenital anosmia (CA) is rare comparatively to acquired anosmia. The pathophysiology and the genetic background remain poorly understood. This study aims to review the main clinical and Magnetic Resonance Imaging (MRI) findings to discuss the diagnostic strategy, the pathophysiology and the genetic basis of the different forms of CA.
A series of 60 patients with congenital anosmia was reviewed retrospectively out of 425 non-sinus-related anosmia and compared to the literature data. CA was assessed by Ear Nose Throat (ENT) workup, psychophysical olfactometry and MRI evaluation of olfactory bulbs (OB) and central olfactory structures.
The 60 cases of CA include 16 isolated congenital anosmia and 44 syndromic congenital anosmia especially 20 Bardet Biedl syndrome and 22 Kallmann syndrome. The diagnosis of CA is often overlooked or delayed especially for isolated CA with no or few complaints about olfaction impairment compared to acquired anosmia. MRI shows in most cases hypoplasia or aplasia of OB with a strong correlation between global OB visual evaluation and OB volumetric evaluation for trained radiologists and often central olfactory abnormalities needing 3D MRI imaging.
The pathophysiology involving peripheral and/or central olfactory abnormalities and the involved genetic mechanisms remain poorly understood. Complete genomes sequencing in affected patients and families with well delineated CA (ENT workup, olfactometry, MRI) and studies of different CA animal models constitute a challenge for better understanding of this rare and heterogeneous group of CA.