Quantitative Magnetic Resonance Imaging Evaluation of the Olfactory System in Kallmann Syndrome: Correlation with a Clinical Smell Test

Abstract

Objectives: To measure olfactory bulbs and sulci using dedicated magnetic resonance imaging (MRI) sequences and specific measurement tools in Kallmann syndrome (KS) patients with a well-established genotype and phenotype, as well as correlate MRI findings with a clinical smell test. Methods: MRI was performed in 21 patients with KS and 16 healthy volunteers; olfactory dysfunction was assessed using the Smell Identification Test (UPSIT), a qualitative suprathreshold olfaction test. Coronal turbo spin echo T2-weighted and volumetric T1-weighted gradient echo sequences were acquired in a 1.5T system. ImageJ software was used to obtain olfactory bulb volumes and olfactory sulcus depths and lengths. Data were analyzed with SPSS 15.0 and the Kappa index was used to evaluate the agreement between the UPSIT and MRI. Results: The UPSIT showed 14 patients with anosmia and 6 with moderate hyposmia. Eighteen patients (85%) presented altered rhinencephalon structures in the MRI. Sixteen patients (76%) presented olfactory bulb aplasia (14/16 bilaterally), and these patients presented a total of 16 aplastic sulci. There was moderate agreement between the MRI quantitative evaluation and the UPSIT (overall Kappa = 0.55), but when considering the presence of aplastic bulbs and anosmia, we found almost perfect agreement (Kappa = 0.87). Three patients had normal rhinencephalon structures, including one with a KAL1 gene mutation. Conclusion: Olfactory bulb and sulcus aplasia were the most common findings in KS patients. We objectively demonstrated agreement between MRI findings and the smell test, especially the presence of bulb aplasia and anosmia. Therefore, our findings help ascertain MRI accuracy in the diagnosis of KS, differentiating patients with hypogonadotropic hypogonadism with an apparently normal or difficult to evaluate sense of smell.