Pathology of the Olfactory Nerve

Prevalence and clinical correlations of olfactory recess dilatation in MRI studies of the feline brain

The ability to differentiate clinical ventriculomegaly from incidental ventricular enlargement remains a challenge in veterinary radiology. Dilatation of one or both olfactory lobe recesses is occasionally seen on MRI of the brain in otherwise normal cats. The purpose of this study was therefore to determine the prevalence of this finding within a population of neurologically normal and neurologically abnormal cats, and to investigate associations with signalment, clinical and neurological examination findings, and MRI features. An observational retrospective cohort study was performed, and archived records were searched for cats that had undergone MRI of the head, including the olfactory lobes. Medical data and MRI parameters were recorded. One hundred fifty-one cats were included, with olfactory recess dilatation present in 56 cats. In 16 neurologically normal cats, olfactory recess dilatation was the only MRI finding. Olfactory recess dilatation was not associated with age, sex, breed, or with the presence of nasal disease. A significant association was found between generalized ventriculomegaly (P = 0.001) and the presence of CSF abnormalities (P = 0.036). Eleven percent of our cohort (16/151) demonstrated olfactory recess dilatation in the absence of other neurological or structural intracranial disease, suggesting that this may be seen as a normal variation in some cats.

A new biomarker combining multimodal MRI radiomics and clinical indicators for differentiating inverted papilloma from nasal polyp invaded the olfactory nerve possibly

Background and purpose

Inverted papilloma (IP) and nasal polyp (NP), as two benign lesions, are difficult to distinguish on MRI imaging and clinically, especially in predicting whether the olfactory nerve is damaged, which is an important aspect of treatment and prognosis. We plan to establish a new biomarker to distinguish IP and NP that may invade the olfactory nerve, and to analyze its diagnostic efficacy.

Materials and methods

A total of 74 cases of IP and 55 cases of NP were collected. A total of 80% of 129 patients were used as the training set (59 IP and 44 NP); the remaining were used as the testing set. As a multimodal study (two MRI sequences and clinical indicators), preoperative MR images including T2-weighted magnetic resonance imaging (T2-WI) and contrast-enhanced T1-weighted magnetic resonance imaging (CE-T1WI) were collected. Radiomic features were extracted from MR images. Then, the least absolute shrinkage and selection operator (LASSO) regression method was used to decrease the high degree of redundancy and irrelevance. Subsequently, the radiomics model is constructed by the rad scoring formula. The area under the curve (AUC), accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the model have been calculated. Finally, the decision curve analysis (DCA) is used to evaluate the clinical practicability of the model.

Results

There were significant differences in age, nasal bleeding, and hyposmia between the two lesions (p < 0.05). In total, 1,906 radiomic features were extracted from T2-WI and CE-T1WI images. After feature selection, using 12 key features to bulid model. AUC, sensitivity, specificity, and accuracy on the testing cohort of the optimal model were, respectively, 0.9121, 0.828, 0.9091, and 0.899. AUC on the testing cohort of the optimal model was 0.9121; in addition, sensitivity, specificity, and accuracy were, respectively, 0.828, 0.9091, and 0.899.

Conclusion

A new biomarker combining multimodal MRI radiomics and clinical indicators can effectively distinguish between IP and NP that may invade the olfactory nerve, which can provide a valuable decision basis for individualized treatment.

Proteomic Analysis of the Human Olfactory Bulb

The importance of olfaction to human health and disease is often underappreciated. Olfactory dysfunction has been reported in association with a host of common complex diseases, including neurological diseases such as Alzheimer's disease and Parkinson's disease. For health, olfaction or the sense of smell is also important for most mammals, for optimal engagement with their environment. Indeed, animals have developed sophisticated olfactory systems to detect and interpret the rich information presented to them to assist in day-to-day activities such as locating food sources, differentiating food from poisons, identifying mates, promoting reproduction, avoiding predators, and averting death. In this context, the olfactory bulb is a vital component of the olfactory system receiving sensory information from the axons of the olfactory receptor neurons located in the nasal cavity and the first place that processes the olfactory information. We report in this study original observations on the human olfactory bulb proteome in healthy subjects, using a high-resolution mass spectrometry-based proteomic approach. We identified 7750 nonredundant proteins from human olfactory bulbs. Bioinformatics analysis of these proteins showed their involvement in biological processes associated with signal transduction, metabolism, transport, and olfaction. These new observations provide a crucial baseline molecular profile of the human olfactory bulb proteome, and should assist the future discovery of biomarker proteins and novel diagnostics associated with diseases characterized by olfactory dysfunction.

Cranial Nerve Foramina Part I: A Review of the Anatomy and Pathology of Cranial Nerve Foramina of the Anterior and Middle Fossa

Cranial nerve foramina are integral exits from the confines of the skull. Despite their significance in cranial nerve pathologies, there has been no comprehensive anatomical review of these structures. Owing to the extensive nature of this topic, Part I of our review, presented here, focuses on the foramina of the anterior and middle cranial fossae, discussing each foramen's shape, orientation, size, surrounding structures, and structures that traverse them. Furthermore, by comparing the size of each foramen against the cross-sectional areas of its contents, we estimate the amount of free space in each. We also review lesions that can obstruct the foramina and discuss their clinical consequences.

Longitudinal Testing of Olfactory and Gustatory Function in Patients with Multiple Sclerosis

Background

The aim of the study was to investigate changes of the olfactory and gustatory capacity in patients with multiple sclerosis (MS).

Methodology

20 MS patients were tested longitudinally for 3 years after initial testing. The Threshold Discrimination Identification test (TDI) was used for subjective olfactometry. Objective olfactometry was performed by registering olfactory evoked potentials (OEP) by EEG. The Taste Strip Test (TST) was used for gustatory testing.

Results

45% of the patients showed olfactory dysfunction in the follow-up TDI test and 50% showed delayed OEP´s. 20% of the patients showed gustatory dysfunction on follow-up visit. The patients showed mild disease activity with 0,3 ± 0,5 relapses over the testing period and no significant change of their olfactory and gustatory capacity. The olfactory capacity for the discrimination of odors correlated inversely with the number of relapses (r = -0.5, p ≤ 0.05). The patients were aware of their olfactory deficit.

Conclusions

Olfactory and gustatory dysfunction is a symptom in MS patients and may be a useful parameter to estimate disease progression in MS patients. As the discrimination of odors is processed in higher central regions of the central nervous system (CNS), the results suggest that olfactory dysfunction could be due to CNS damage.

Visualization of the olfactory nerve using constructive interference in steady state magnetic resonance imaging

PURPOSE

The olfactory nerve (OlfN) is a small neural structure with inconsistent visualization on neuroimages. The aim of this study was to delineate the intracranial course of the OlfN using constructive interference in steady state magnetic resonance (MR) imaging.

METHODS

A total of 168 patients were enrolled in this study. Following initial examinations with conventional MR sequences, constructive interference in steady-state sequence (CISS) was performed in coronal and axial sections.

RESULTS

On coronal sections, the OlfN was entirely visualized in 90 % of patients on the right and 92 % on the left, coursing along the olfactory sulcus. Complete visualization of the OlfN occurred in 100 % of patients on serial axial images. The OlfN was classified into four portions based on the topographical differences and surrounding structures. The olfactory fossa exhibited considerable variability at the midlevel of the olfactory bulb on coronal images. Characteristic appearance of the OlfN with respect to age range or gender was not observed.

CONCLUSIONS

The OlfN follows a highly consistent course along the olfactory sulcus. Thin-sliced, CISS sequences are useful for consistent visualization of the OlfN.

A voxel-based morphometry study of anosmic patients

OBJECTIVE

The aim of our study was to compare volume change in grey matter (GM) and white matter (WM) in a group of subjects with anosmia and a healthy control group. We tried to find a regular pattern of atrophy within and between GM and WM and to determine whether any particular areas are more sensitive to olfactory injury.

METHODS

There were 19 anosmic patients and 20 age- and sex-matched control subjects. We acquired MR images on a 3-T scanner and performed voxel-based morphometry using the VBM8 toolbox and SPM8 in a MATLAB® (MathWorks®, Natick, MA) environment.

RESULTS

Patients with anosmia showed a significant decrease in GM volume, mainly in the anterior cingulate cortex, middle temporal gyrus, superior temporal gyrus, fusiform gyrus, supramarginal gyrus, superior frontal gyrus, middle frontal gyrus, middle occipital gyrus, anterior insular cortex and cerebellum. In addition, we observed volume decreases in smaller areas such as the piriform cortex, the inferior temporal gyrus, the precuneus and the subcallosal gyrus. All WM areas with atrophy were near those GM areas that experienced volume loss. There was more volume atrophy in GM areas corresponding to WM areas with more volume loss. Atrophy increased with disease duration.

CONCLUSION

There is simultaneous atrophy in GM and WM, and the degree of atrophy is greater with longer disease duration. Different GM and WM areas have different sensitivities to olfactory injury.

ADVANCES IN KNOWLEDGE

This study examines the atrophy pattern in and between GM and WM-a subject that has not been widely researched previously.

The olfactory system

Any dysfunction in olfaction requires a radiological exploration comprising the nasal cavity, the anterior base of the skull, in particular the frontal and temporal lobes. MRI is the reference examination, due to the frontal plane and the T1, T2 volume maps. In the child, aplasia of the olfactory bulbs falls within a polymalformation (CHARGE) or endocrine (Kallman) context. In the adult, rhino sinus disease and meningiomas are the most common etiologies. Frontal or temporal impairment: tumoral or vascular and neurodegenerative disorders (Parkinson's disease) may accompany a loss of olfaction.

Decreased olfactory bulb volume in idiopathic Parkinson's disease detected by 3.0-tesla magnetic resonance imaging

A number of neuropathological studies have demonstrated that the olfactory system is among the first brain regions affected in Parkinson's disease (PD). These findings correlate with pathophysiological and pathological data that show a loss in olfactory bulb (OB) volume in patients with PD. However, to date, MRI has not been a reliable method for the in vivo detection of this volumetric loss in PD. Using a 3.0-Tesla MRI constructive interference in the steady-state sequence, OB volume was evaluated in patients with PD (n = 16) and healthy control subjects (n = 16). A significant loss of OB volume was observed in patients with PD, compared to the healthy control group (91.2 ± 15.72 versus 131.4 ± 24.56 mm(3) , respectively). Specifically, decreased height of the left OB appears to be a reliable parameter that is adaptable to clinical practice and significantly correlates with OB volume loss in patients with idiopathic PD. Measuring both the volume and height of the OB by MRI may be a valuable method for the clinical investigation of PD.

In vitro comparison of water displacement method and 3 Tesla MRI for MR-volumetry of the olfactory bulb: which sequence is appropriate?

RATIONALE AND OBJECTIVES

Magnetic resonance imaging olfactory bulb (OB) volumetry (OBV) is already used as a complementary prognostic tool to assess olfactory disorders. However, a reference standard in imaging for OBV has not been established. The aim of this in vitro study was to compare volumetric results of different magnetic resonance sequences for OBV at 3 T to genuine OB volumes measured by water displacement.

MATERIALS AND METHODS

The volumes of 15 human cadaveric OBs were measured using the water displacement method in this institutional review board-approved prospective study. The magnetic resonance imaging protocol at 3 T included constructive interference in steady state (CISS), T2-weighted (T2w) three-dimensional (3D) sampling perfection with application-optimized contrasts using different flip-angle evolutions (SPACE), T2w two-dimensional (2D) turbo spin-echo (TSE), and T1-weighted (T1w) 3D fast low-angle shot (FLASH) sequences. Two blinded observers independently performed two OB volumetric assessments per bulbus and sequence. Intraobserver and interobserver reliabilities were assessed by intraclass correlation coefficients. Bland-Altman plots were analyzed to evaluate systematic biases and concordance correlation coefficients to assess reproducibility.

RESULTS

For both observers, intraclass correlation coefficient analysis yielded almost perfect results for intraobserver reliability (CISS, 0.94-0.98; T2w 3D SPACE, 0.93-0.98; T2w 2D TSE, 0.98-0.98; T1w 3D FLASH, 0.95-0.99). Interobserver reliability showed almost perfect agreement for all sequences (CISS, 0.98; T2w 3D SPACE, 0.89; T2w 2D TSE, 0.93; T1w 3D FLASH, 0.97). The CISS sequence yielded the highest mean concordance correlation coefficient (0.95) and the highest combination of precision (0.97) and accuracy (0.98) values. In comparison with the water displacement method, Bland-Altman analyses revealed the lowest systematic bias (-0.5%) for the CISS sequence, followed by T1w 3D FLASH (-1.3%), T2w 3D SPACE (-7.5%), and T2w 2D TSE (-10.9%) sequences.

CONCLUSIONS

Compared to the water displacement method, the CISS sequence is suited best to validly and reliably measure OB volumes because of its highest values for accuracy and precision and lowest systematic bias.

Reproducibility and repeatability of volumetric measurements for olfactory bulb volumetry: which method is appropriate? An update using 3 Tesla MRI

RATIONALE AND OBJECTIVES

The aim of this study was to compare different sequences for olfactory bulb volumetry using 3-T magnetic resonance imaging, evaluating reproducibility, repeatability, and systematic biases.

MATERIALS AND METHODS

Twenty-two volunteers underwent 3-T magnetic resonance imaging of the frontal skull base in this prospective study. Imaging included constructive interference in steady state (CISS), T2-weighted (T2w) three-dimensional (3D) sampling perfection with application-optimized contrasts using different flip-angle evolutions, and T2w two-dimensional (2D) turbo spin-echo sequences. Two observers independently performed two olfactory bulb volumetric studies per bulb and sequence. Intraobserver and interobserver reliability was assessed using intraclass correlation coefficients. For the evaluation of reproducibility, concordance correlation coefficients were determined, and for repeatability and systematic biases, Bland-Altman plots were analyzed.

RESULTS

Intraclass correlation coefficient analysis of the specialized observer yielded almost perfect results for intraobserver reliability (0.94, 0.85, and 0.93 for the CISS, T2w 3D, and T2w 2D sequences, respectively). For the less experienced observer, the results were 0.86 0.78, and 0.74 for the CISS, T2w 3D, and T2w 2D sequences, respectively. Interobserver reliability showed almost perfect agreement for all sequences (0.92, 0.86, and 0.86, respectively). The CISS sequence yielded the highest concordance correlation coefficient (0.84), precision (0.85), and accuracy (0.99). Bland-Altman plot analyses revealed the lowest repeatability coefficients for the T2w 2D sequence. Volumetric measurements of T2w 2D imaging showed systematically lower volumetric results compared to the CISS sequence (-22.7%) and the T2w 3D sequence (-8.3%).

CONCLUSIONS

Comparison of three imaging sequences for olfactory bulb volumetry yielded the best values for the CISS sequence in terms of intraobserver and interobserver reliability, reproducibility, accuracy, and precision. Given that even less experienced observers achieve almost perfect results, the CISS sequence is recommended for olfactory bulb volumetry.

Structural correlates of taste and smell loss in encephalitis disseminata

Background

Olfactory dysfunction in MS patients is reported in the literature. MRI of the olfactory bulb (OB) is discussed as a promising new testing method for measuring olfactory function (OF).

Aim of this study was to explore reasons for and optimize the detection of olfactory dysfunction in MS patients with MRI.

Materials and Methods

OB and olfactory brain volume was assessed within 34 MS patients by manual segmentation. Olfactory function was tested using the Threshold-Discrimination-Identification-Test (TDI), gustatory function was tested using Taste Strips (TST).

Results

41% of the MS patients displayed olfactory dysfunction (8% of the control group), 16% displayed gustatory dysfunction (5% of the control group). There was a correlation between the OB volume and the number and volume of MS lesions in the olfactory brain. Olfactory brain volume correlated with the volume of lesions in the olfactory brain and the EDSS score. The TST score correlated with the number and volume of lesions in the olfactory brain.

Conclusion

The correlation between a higher number and volume of MS lesions with a decreased OB and olfactory brain volume could help to explain olfactory dysfunction.

Visual grading characteristics (VGC) analysis of diagnostic image quality for high resolution 3 Tesla MRI volumetry of the olfactory bulb

RATIONALE AND OBJECTIVES

The aim of this study was to evaluate the suitability of 3-T magnetic resonance imaging (MRI) for olfactory bulb volumetry, comparing image quality obtained using different sequences on the basis of physical characteristics in combination with observer performance.

MATERIALS AND METHODS

Twenty-two healthy volunteers (11 men, 11 women; mean age, 25 years) underwent 3-T MRI of the frontal skull base in this prospective study. Imaging was performed using a constructive interference in steady state (CISS) three-dimensional Fourier transformation sequence, a three-dimensional T2-weighted (3D-T2w) sequence, and a two-dimensional T2-weighted (2D-T2w) sequence. The relative performance of sequences was assessed using visual grading characteristic analysis. Interobserver agreement was assessed using κ statistics. For evaluation of physical image quality characteristics, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated and compared using Wilcoxon's test. SNR and CNR measurements were correlated with visual grading results.

RESULTS

Visual grading characteristic analysis showed significantly better image quality ratings for the CISS sequence compared to the 3D-T2w and 2D-T2w sequence, and the 2D-T2w sequence performed significantly better compared to the 3D-T2w sequence (P < .001). Interobserver agreement was substantial (κ = 0.66-0.73). Wilcoxon's test revealed significantly higher SNR and CNR values for the 2D-T2w sequence compared to the 3D-T2w and CISS sequences, and SNR and CNR values for the 3D-T2w sequence were significantly higher compared to those for the CISS sequence (P < .001 for each). Significant correlation between SNR and CNR and visual grading was found for the 3D-T2w sequence (SNR: ρ = 0.510, P = .015; CNR: ρ = 0.546, P = .009).

CONCLUSIONS

High-resolution 3-T MRI resulted in excellent values for SNR and CNR, suggesting the appropriateness of the sequences for olfactory bulb MRI volumetry. Visual grading characteristic analysis revealed the CISS sequence to be the most suitable for olfactory bulb volumetry.

Gray matter alterations in parosmia

Parosmia is a common olfactory disorder. In this condition, odors are perceived in a different quality than usual. This distorted olfactory percept is typically reported to be unpleasant. Little is known about the pathophysiology of this phenomenon. Previous studies demonstrated smaller volumes of the olfactory bulbs in patients with parosmia compared to subjects without parosmia. In order to investigate structural brain alterations in areas beyond the olfactory bulb, in the current study voxel-based morphometry was applied. A group of 22 parosmic patients was compared with control subjects matched for age- and sex, who exhibited a similar performance in olfactory tests. Performing a whole brain analysis, we found profound gray matter volume loss in the left anterior insula in parosmic patients. In an additional volume of interest analysis including primary and secondary olfactory areas, we also found volume loss in the right anterior insula, the anterior cingulate cortex, the hippocampus bilaterally, and the left medial orbitofrontal cortex. Many of these areas are critically involved in olfactory quality discrimination and odor memory. The present results indicate that reduced gray matter volume in brain regions supporting odor discrimination and memory is related to disturbed olfactory sensation in parosmia.

Increasing olfactory bulb volume due to treatment of chronic rhinosinusitis--a longitudinal study

Differentiation of progenitor cells into neurons in the olfactory bulb depends on olfactory stimulation that can lead to an increase in olfactory bulb volume. In this study, we investigated whether the human olfactory bulb volume increases with increasing olfactory function due to treatment of chronic rhinosinusitis. Nineteen patients with chronic rhinosinusitis were investigated before and after treatment. For comparison, additional measurements were performed in 18 healthy volunteers. Volumetric measurements of the olfactory bulb were based on planimetric manual contouring of magnetic resonance scans. Olfactory function was evaluated separately for each nostril using tests for odour threshold, odour discrimination and odour identification. Measurements were performed on two occasions, 3 months apart. In healthy controls, the olfactory bulb volume did not change significantly between the two measurements. In contrast, the olfactory bulb volume in patients increased significantly from the initial 64.5 +/- 3.2 to 70.0 +/- 3.5 mm(3) on the left side (P = 0.02) and from 60.9 +/- 3.5 to 72.4 +/- 2.8 mm(3) on the right side (P < 0.001). The increase in olfactory bulb volume correlated significantly with an increase in odour thresholds (r = 0.60, P = 0.006, left side; r = 0.49, P = 0.03, right side), but not with changes in odour discrimination or odour identification. Results of this study support the idea that stimulation of olfactory receptor neurons impacts on the cell death in the olfactory bulb, not only in rodents but also in humans. To our knowledge, this is the first longitudinal study that describes an enlargement of the human olfactory bulb due to improvement of peripheral olfactory function.