Saturday, September 20, 2014
Thursday, September 18, 2014
Assessment of Meniere's disease from a radiological aspect – saccular otoconia as a cause of Meniere's disease?
I found this to be a very interesting study out of the Osaka City University Graduate School of Medicine. Even better, it's a full-text article!
First of all, I think it is very exciting that the use of 3D cone beam CT is being used to visualize the inner ear because, up until now, the ability to see the structures of the cochlea and membranous labyrinth have only been possible using postmortem specimens. In other words, after the poor person has died. But another exciting aspect of this relatively short report is that it not only nicely summarizes the variety of potential etiologies, or causes, of Meniere's symptoms, but it also suggests hope for future treatments which might be able to return patency of the blocked ducts and hopefully eliminate, or at least greatly reduce, symptoms. Finally, the findings of this study seem to suggest to me that perhaps the varying degrees and types of hearing loss and vestibular symptoms those of us with Meniere's disease suffer might be dependent on the varying degree of occlusion and which or how many ducts are affected.
P.S. Go straight to the article to see the cool color images produced by the 3D cone beam CT.
Assessment of Meniere's disease from a radiological aspect – saccular otoconia as a cause of Meniere's disease?
Hideo Yamane,corresponding author 1 Kishiko Sunami, 1 Hiroyoshi Iguchi, 1 Hiramori Sakamoto, 1 Toshio Imoto, 1 and Helge Rask-Andersen 2
Author information ► Article notes ► Copyright and License information ►
This article has been cited by other articles in PMC.
Abstract
Significant reduced visualization of the reuniting duct (ductus reuniens; RD), saccular duct (SD) and endolymphatic sinus (ES) in Meniere's disease (MD) compared with normal control ears on three-dimensional (3D) CT imaging suggests the blockage of endolymphatic flow there with radiodense substances, which may be explained by dislodged otoconia from the saccule. These structures could be involved in the pathogenesis of MD.
Objective
This study was designed to visualize and assess the RD, SD and ES in patients with MD using 3D CT.
Methods
Sixty-two patients with a definite diagnose of unilateral MD, based on criteria proposed by the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), were compared with contralateral ears and normal controls (26 ears) using 3D CT. The RD, SD and ES were scrutinized for patency on 3D CT images.
Results
MD ears showed loss of continuity of the RD, SD and ES based on evaluation of 3D CT images, and differed significantly from normal healthy control ears (p < 0.01).
Keywords: Saccular duct, saccule, endolymphatic hydrops, endolymphatic duct, CT image, bilaterality
Introduction
The etiology of Meniere's disease (MD) remains a riddle in spite of many studies. Most such studies are based on the idea of endolympatic hydrops [1,2]. Even though the existence of a ‘longitudinal flow’ has been challenged experimentally by some researchers in recent years, a disturbance of endolymph circulation within the duct system is generally agreed to be an important factor for generation of endolymphatic hydrops in MD [3,4].
We previously reported on the visualization of the reuniting duct (RD) and saccular duct (SD) and endolymphatic sinus (ES) of the human inner ear by analysing their bony grooves using three-dimensional (3D) cone beam CT images [5,6]. As the RD, SD and ES each lodge onto these bony grooves, analysis of the grooves can yield information on the condition of the RD, SD and ES. Using this strategy, we reported that MD patients, defined as grade 3 by the criteria of MD from the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), showed significant discontinuity of the bony groove of the RD in comparison with normal ears. This discontinuity suggests that the RD may be blocked by a radiodense substance [7], and this substance could represent dislodged saccular otoconia.
The saccule contains two ducts, the RD and the SD. They are believed to convey endolymph or pressure release between the endolymphatic compartments. Investigating these two ducts may be crucial when analysing MD patients from the viewpoint of patent ‘longitudinal flow’. In the present study we report on the incidence of patency of these two ducts and the ES in MD patients compared to controls.
Material and methods
Subjects
We studied 62 patients (29 males and 33 females; mean age 55.5 years, range 25–86 years) with diagnosed unilateral MD as defined by the criteria of the Committee on Hearing and Equilibrium of the AAO-HNS. The affected ears of patients with MD were compared with the non-affected contralateral ears and the bilateral healthy ears in 13 volunteers (6 males and 7 females, mean age 57.9 years, range 35–79 years). Four frequencies at 0.5, 1, 2 and 4 kHz were used to calculate pure tone averages. Although a 3 kHz threshold is included in the four pure tone averages used for definition of MD by AAO-HNS, 3 kHz is not commonly used in Japan, and 4 kHz was substituted for 3 kHz in this study.
Approval for this study was obtained from the ethics committee of Osaka City University Graduate School of Medicine.
Analysis of CT image
The temporal bones were examined using 3D cone beam CT (3D Accuitomo; J. Morita Mfg Corp., Kyoto, Japan) using the same conditions as reported previously [5,6]: 80 kV; 6 mA; voxel, 0.125 mm × 0.125 mm × 0.125 mm; slice thickness, 0.5 mm. The CT images were taken in a region of interest of diameter 6 cm and height 6 cm. Reconstructed 3D images of the inner ear were obtained by rendering software (IVIEW) in perspective view with a viewing angle of 15° and 0.25 mm voxel size (0.25 mm × 0.25 mm × 0.25 mm).
We previously reported how to reduce artefacts due to rendering effects [5,6] by comparing the findings of a cadaver temporal bone and its 3D CT image using several landmarks. In the present investigation of the image patterns of the RD, SD and ES, we adopted an additional image in which the common crus formed a horizontal line, so rotation would not change the view from directly above.
We evaluated the patency of the grooves of the RD, SD and ES (Figure 1). The patency of the RD was assessed on the orifice of the saccule to the RD based on our previous report [7]. The patencies of the SD and ES were analysed in the same manner by assessing the continuity of their bony grooves [6]. In this study the appearances of the grooves of the RD, SD and ES as not fully recognized was defined as closed and any other state was defined as open to avoid the weak point of the subjective visual evaluation of 3D CT images (Figure 2).
Figure 1.
Figure 1.
3D CT image of the reuniting duct (RD), saccular duct (SD) and endolymphatic sinus (ES) of a healthy volunteer's ear (left), cadaver's ear (upper right), and schematic view (lower right). All these views are left ears. Red arrows show the RD and yellow ...
Figure 2.
Figure 2.
Drawings demonstrating the patency of the reuniting duct (RD), saccular duct (SD) and endolymphatic sinus (ES) on 3D CT images. When otoconia are dislodged into the RD, SD or ES, they lose continuity of the surface of their bony grooves and become vague ...
Additionally, we examined CT images of a cadaver with a small piece of muscle or small amount of calcium carbonate on the bony grooves of SD and ES to assess changes in the CT images, as in our previous report [7].
Statistical analysis
The 62 patients were analyzed in comparison with the normal subjects. The incidence of abnormal images of the bony grooves of those portions in affected ears in MD patients was compared with the non-affected contralateral ears and control volunteer ears and analysed by Yates 2 × 2 chi-squared test.
Results
Findings of RD aspects
Figures 3 and and44 show representative views of different patencies of the RD, SD and ES. Of the ears on the affected side of MD patients (Figures 3A and and4A),4A), 37% (23/62)) had closed RD compared with 9.7% (6/62) of the ears on the non-affected side (Table I). None (0/26) were closed in the normal group (Figures 3B and and4B).4B). There were significant differences between the ears on the affected side of MD patients and normal ears, and between the affected ears and the non-affected ears (p < 0.01) (Figure 5). There was no significant difference between non-affected ears of MD patients and normal ears (p = 0.078).
Figure 3.
Figure 3.
Representative views of the left ear of a patient with Meniere's disease (MD) (A) and a volunteer's healthy ear (B). (A) Although the outline of the bony groove of the reuniting duct (RD) (arrows), saccular duct (SD) and endolymphatic sinus (ES) can be ...
Figure 4.
Figure 4.
Representative views of the right ear of a patient with Meniere's disease (MD) (A) and a volunteer's healthy ear (B). (A) Both the bony grooves of the reuniting duct (RD) and the endolymphatic sinus (ES) are fully occupied by a dense, bony substance and ...
Table I.
Table I.
Status of the reuniting duct (RD), saccular duct (SD) and endolymphatic sinus (ES) in 62 patients with Meniere's disease (MD) and 13 healthy volunteers.
Figure 5.
Figure 5.
Distribution pattern of the reuniting duct (RD) in affected and non-affected ears of patients with Meniere's disease (MD) and healthy ears of volunteers.
Findings of SD aspects
The patencies of the affected and non-affected ears of MD were 51.6% (32/62) and 16.1% (12/62), respectively (Table I). In contrast, all the SDs (26/26) were patent in the healthy ears (Figures 3B and and4B).4B). There were significant differences between the affected ears and healthy ears and between the affected ears and the non-affected ears (p < 0.01). There was a slight but significant difference between the non-affected ears and healthy ears (p = 0.015) (Figure 6).
Figure 6.
Figure 6.
Distribution pattern of the saccular duct (SD) in affected and non-affected ears of patients with Meniere's disease (MD) and healthy ears of volunteers.
Findings of ES aspects
The distribution pattern of the ES resembled that of the SD. The patencies of the affected ears and non-affected ears of MD patients were 64.5% (40/62) and 17.7% (11/62), respectively (Table I). All the ESs (26/26) were patent in the healthy ears (Figures 3B and and4B).4B). There were significant differences between the affected ears and healthy ears and between the affected ears and the non-affected ears (p < 0.01). There was a slight difference between the non-affected ears and healthy ears (p = 0.030) (Figure 7).
Figure 7.
Figure 7.
Distribution pattern of the endolymphatic sinus (ES) in affected and non-affected ears of patients with Meniere's disease (MD) and healthy ears of volunteers.
Findings in the SD and ES of a cadaver treated with CaCO3 and soft tissue fragments
The bony grooves of the SD and ES treated with CaCO3 appeared vague (Figure 8A), but those with muscle fragments were not affected (Figure 8B).
Figure 8.
Figure 8.
3D CT views of a cadaver temporal bone. The bony grooves underlining the saccular duct (SD) and the endolymphatic sinus (ES) treated with CaCO3 (A) appear vague compared with those treated with muscle fragments (B). Note the difference in continuity of ...
Discussion
We could demonstrate differences in visualization or patency of the RD, SD and ES between the affected ears of MD patients and normal ears, suggesting that the RD, SD or ES in MD ears may be partly or entirely occluded compared with healthy ears. The reduced visualization of the RD, SD and ES suggests that these ducts were involved as lesions of MD.
Debris, pathogens or unusual substances in the inner ear can be transported in these narrow ducts and become obstacles to the pathway of longitudinal flow of endolymph resulting in endolymphatic hydrops.
We speculate that a reasonable explanation for this reduced visualization may be an occlusion caused by dislodged otoconia from the saccule. This is based on experimental findings from cadavers showing that the bony groove appears vague when covered with CaCO3 but not when covered with muscle fragments. The data from the present and previous studies [7] suggest that the occlusion may be situated between the saccule and the RD or the SD and the ES.
Saccular otoconia could be dislodged by various causes such as aging as the natural fate, infection, disturbance of blood circulation, trauma, etc., and the dislodged otoconia from the saccule can disperse into the surrounding membranous labyrinth [8,9].
If otoconia fall into such a narrow pathway, the RD to the cochlea or the SD and ES to the endolymphatic duct, they could disturb the endolymphatic flow.
Although saccular otoconia are more susceptible than those of the utricle [10], the incidence of MD patients is not so high in comparison with benign paroxysmal positional vertigo (BPPV) possibly caused by dislodged utricular otoconia [11]. We do not have conclusive data proving this. However, some speculation from our present results may answer this question. The risk of saccular otoconia falling into the RD may not be so high because of its narrowness, even if it is near the saccular otolithic membrane.
The longitudinal endolymph may work to oppose saccular otoconia falling into the RD. On the other hand, the SD and ES are in the path of the anterograde endolymph system. Therefore, the SD (51.6%) and ES (64.5%) may be more occluded than the RD (37%). The character of MD may be due to the rate of occlusion of these narrow ducts.
Histological studies reported that the endolympatic duct (ED) was obstructed with fibrous tissue, basophilic substance or bone in MD [12] and a radiological study also showed narrow and poor development of the ED in MD [13]. The lesions of the ED may have a similar pathology to those of the SD and ES because all these regions are connected as successive membranous pathways, which could support our hypothesis that dislodged saccular otoconia could be a cause of MD. However, more precise investigation of these areas of the human temporal bone in MD is necessary.
Although the non-affected ears in patients with MD showed a similar RD pattern to the affected ears, the similarity was not statistically supported. On the other hand, there were slight differences in the patency of the SD and ES between the non-affected ears and healthy ears. This tendency of occlusion in the SD and ES of the non-affected ears of MD patients suggests that the contralateral non-affected ears may also be challenged but functionally compensated. Earlier acoustic biasing experiments have shown that incipient endolymphatic hydrops may exist in the healthy contralateral ear in MD.
Bilateral engagement of MD varies according to different authors. The longer the duration of the disease the more frequent is the incidence of bilateral disease [14]. In a recent German study where the long-term course of MD was revisited, as many as 35% of subjects suffered from MD in both ears after 10 years and 47% after 20 years [15]. Some studies show a low bilateral incidence (5%) while audiometric low-tone changes occur more frequently (16%) [16]. Also, the modulation depth was found to be significantly reduced in the contralateral non-symptomatic ears of MD patients using low-frequency masking to diagnose endolymphatic hydrops [17]. This has led to the conception that MD is basically a bilateral disease with differing expression in the two ears. In addition, histopathological changes have been described to a large extent in the contralateral temporal bone in patients with unilateral MD [18]. Genetic alterations such as single nucelotide polymorphisms have been described in patients with bilateral MD [19]. The onset of MD has also been found to be earlier when both ears are affected [20]. Although we could not verify signs of bilateralism in our patients with MD in the present unilateral cases, the unilateral group may have included some bilateral cases. This is supported by our 3D CT findings. However, bilaterality of MD must be fully investigated in a future study.
We hypothesize that MD is a pathological condition brought about by saccular dislodged otoconia due to several causes, obstructing the narrow paths of the endolymph, based on the etiology of BPPV caused by dislodged otoconia from the utricle (Figure 9). Although we must investigate many factors of MD and the mechanism of MD attack in the future, the opening of these narrow paths could be one effective therapy for MD.
Figure 9.
Figure 9.
Hypothetical view of blockage of the reuniting duct (RD), saccular duct (SD) and endolymphatic sinus (ES) by dislodged otoconia from the saccule in patients with Meniere's disease (MD). ED, endolymphatic duct; EnS, endolymphatic sac; L, lateral semicircular ...
We evaluated the patency of the RD, SD and ES by 3D CT imaging, reflected by their bony grooves and not the actual ducts and ES. We thus obtained no definitive data on the degree of obstruction using the present 3D CT images.
In addition, the differences on 3D CT images among the various stages of MD that are categorized by degree of hearing deterioration must be investigated in the future.
Acknowledgements
We are indebted to Dr Hiroshi Aradate of J. Morita Corp. for valuable technical assistance.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
References
[1] Yamakawa K. Über die pathologishe Veränderung bei einem Meniere-Kranken. J Otorhinolarngol Soc (Jpn) 1938;44:2310–2.
[2] Hallpike CS, Cairns H. Observation on the pathology of Meniere's syndrome. J Laryngol Otol. 1938;53:625–55.
[3] Kimura RS, Schuknecht HF. Membranous hydrops in the inner ear of the guinea pig after obliteration of the endolymphatic sac. Pract Otorhinolaryngol. 1965;27:343–54.
[4] Schuknecht HF, Rüther A. Blockage of longitudinal flow in the endolymphatic hydrops. Eur Arch Otorhinolaryngol. 1991;248:209–17. [PubMed]
[5] Yamane H, Takayama M, Sunami K, Sakamoto H, Anniko M. Assessment of the reuniting duct by three-dimensional CT rendering. Acta Otolaryngol. 2009;129:1166–8. [PubMed]
[6] Yamane H, Takayama M, Sunami K, Sakamoto H, Imoto T, Anniko M. Visualization and assessment of saccular duct and endolymphatic sinus. Acta Otolaryngol. 2011;131:469–73. [PMC free article] [PubMed]
[7] Yamane H, Takayama M, Sunami K, Sakamoto H, Imoto T, Anniko M. Blockage of reuniting duct in Meniere's disease. Acta Otolaryngol. 2010;130:233–9. [PubMed]
[8] Yamane H, Imoto T, Nakai Y, Igarashi M, Rask-Andersen H. Otoconia degradation. Acta Otolaryngol Suppl. 1984;406:263–70. [PubMed]
[9] Gussen R, Adkins WY., Jr Saccule degeneration and ductus reunions obstruction. Arch Otolaryngol. 1974;99:132–5. [PubMed]
[10] Johnsson L-G. Degenerative changes and anomalies of the vestibular system in man. Laryngoscope. 1971;81:1682–94. [PubMed]
[11] Schuknecht HF. Cupulolithiasis. Arch Otolaryngol. 1969;90:765–78. [PubMed]
[12] Schuknecht HF. Pathology of the ear. 2nd edition. Pennsylvania: Lea & Febiger; 1993. Disorders of unknown or multiple causes; pp. 449–553. p.
[13] Yamamoto E, Mizukaimi C, Isono M, Ohmura M, Hirono Y. Observation of the external aperture of the vestibular duct using three-dimensional surface reconstruction imaging. Laryngoscope. 1991;101:480–3. [PubMed]
[14] Friberg U, Stahle J, Svedberg A. The natural course of Meniere's disease. Acta Otolaryngol Suppl. 1984;406:72–7. [PubMed]
[15] Huppert D, Strupp M, Brandt T. Long-term course of Meniere's disease revisited. Acta Otolaryngol. 2010;130:644–51. [PubMed]
[16] Perez R, Chen JM, Nedzelski JM. The status of the contralateral ear in established unilateral Meniere's disease. Laryngoscope. 2004;114:1373–6. [PubMed]
[17] Mrowinski D, Scholz G, Krompass S, Nubel K. Diagnosis of endolymphatic hydrops by low-frequency masking. Audiol Neurootol. 1997;1:125–34. [PubMed]
[18] Kariya S, Cureoglu S, Fukushima H, Kusunoki T, Schachern PA, Nishizaki K, et al. Histopathologic changes of contralateral human temporal bone in unilateral Meniere's disease. Otol Neurotol. 2007;28:1063–8. [PubMed]
[19] Lopez-Escamez JA, Saenz-Lopez P, Acosta L, Moreno A, Gazquez I, Perez-Garrigues H, et al. Association of a functional polymorphism of PTPN22 encoding a lymphoid protein phosphatase in bilateral Meniere's disease. Laryngoscope. 2010;120:103–7. [PubMed]
[20] Chaves AG, Boari L, Lei Munhoz MS. The outcome of patients with Meniere's disease. Braz J Otorhinolaryngol. 2007;73:346–50. [PubMed]
First of all, I think it is very exciting that the use of 3D cone beam CT is being used to visualize the inner ear because, up until now, the ability to see the structures of the cochlea and membranous labyrinth have only been possible using postmortem specimens. In other words, after the poor person has died. But another exciting aspect of this relatively short report is that it not only nicely summarizes the variety of potential etiologies, or causes, of Meniere's symptoms, but it also suggests hope for future treatments which might be able to return patency of the blocked ducts and hopefully eliminate, or at least greatly reduce, symptoms. Finally, the findings of this study seem to suggest to me that perhaps the varying degrees and types of hearing loss and vestibular symptoms those of us with Meniere's disease suffer might be dependent on the varying degree of occlusion and which or how many ducts are affected.
P.S. Go straight to the article to see the cool color images produced by the 3D cone beam CT.
Assessment of Meniere's disease from a radiological aspect – saccular otoconia as a cause of Meniere's disease?
Hideo Yamane,corresponding author 1 Kishiko Sunami, 1 Hiroyoshi Iguchi, 1 Hiramori Sakamoto, 1 Toshio Imoto, 1 and Helge Rask-Andersen 2
Author information ► Article notes ► Copyright and License information ►
This article has been cited by other articles in PMC.
Abstract
Significant reduced visualization of the reuniting duct (ductus reuniens; RD), saccular duct (SD) and endolymphatic sinus (ES) in Meniere's disease (MD) compared with normal control ears on three-dimensional (3D) CT imaging suggests the blockage of endolymphatic flow there with radiodense substances, which may be explained by dislodged otoconia from the saccule. These structures could be involved in the pathogenesis of MD.
Objective
This study was designed to visualize and assess the RD, SD and ES in patients with MD using 3D CT.
Methods
Sixty-two patients with a definite diagnose of unilateral MD, based on criteria proposed by the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), were compared with contralateral ears and normal controls (26 ears) using 3D CT. The RD, SD and ES were scrutinized for patency on 3D CT images.
Results
MD ears showed loss of continuity of the RD, SD and ES based on evaluation of 3D CT images, and differed significantly from normal healthy control ears (p < 0.01).
Keywords: Saccular duct, saccule, endolymphatic hydrops, endolymphatic duct, CT image, bilaterality
Introduction
The etiology of Meniere's disease (MD) remains a riddle in spite of many studies. Most such studies are based on the idea of endolympatic hydrops [1,2]. Even though the existence of a ‘longitudinal flow’ has been challenged experimentally by some researchers in recent years, a disturbance of endolymph circulation within the duct system is generally agreed to be an important factor for generation of endolymphatic hydrops in MD [3,4].
We previously reported on the visualization of the reuniting duct (RD) and saccular duct (SD) and endolymphatic sinus (ES) of the human inner ear by analysing their bony grooves using three-dimensional (3D) cone beam CT images [5,6]. As the RD, SD and ES each lodge onto these bony grooves, analysis of the grooves can yield information on the condition of the RD, SD and ES. Using this strategy, we reported that MD patients, defined as grade 3 by the criteria of MD from the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), showed significant discontinuity of the bony groove of the RD in comparison with normal ears. This discontinuity suggests that the RD may be blocked by a radiodense substance [7], and this substance could represent dislodged saccular otoconia.
The saccule contains two ducts, the RD and the SD. They are believed to convey endolymph or pressure release between the endolymphatic compartments. Investigating these two ducts may be crucial when analysing MD patients from the viewpoint of patent ‘longitudinal flow’. In the present study we report on the incidence of patency of these two ducts and the ES in MD patients compared to controls.
Material and methods
Subjects
We studied 62 patients (29 males and 33 females; mean age 55.5 years, range 25–86 years) with diagnosed unilateral MD as defined by the criteria of the Committee on Hearing and Equilibrium of the AAO-HNS. The affected ears of patients with MD were compared with the non-affected contralateral ears and the bilateral healthy ears in 13 volunteers (6 males and 7 females, mean age 57.9 years, range 35–79 years). Four frequencies at 0.5, 1, 2 and 4 kHz were used to calculate pure tone averages. Although a 3 kHz threshold is included in the four pure tone averages used for definition of MD by AAO-HNS, 3 kHz is not commonly used in Japan, and 4 kHz was substituted for 3 kHz in this study.
Approval for this study was obtained from the ethics committee of Osaka City University Graduate School of Medicine.
Analysis of CT image
The temporal bones were examined using 3D cone beam CT (3D Accuitomo; J. Morita Mfg Corp., Kyoto, Japan) using the same conditions as reported previously [5,6]: 80 kV; 6 mA; voxel, 0.125 mm × 0.125 mm × 0.125 mm; slice thickness, 0.5 mm. The CT images were taken in a region of interest of diameter 6 cm and height 6 cm. Reconstructed 3D images of the inner ear were obtained by rendering software (IVIEW) in perspective view with a viewing angle of 15° and 0.25 mm voxel size (0.25 mm × 0.25 mm × 0.25 mm).
We previously reported how to reduce artefacts due to rendering effects [5,6] by comparing the findings of a cadaver temporal bone and its 3D CT image using several landmarks. In the present investigation of the image patterns of the RD, SD and ES, we adopted an additional image in which the common crus formed a horizontal line, so rotation would not change the view from directly above.
We evaluated the patency of the grooves of the RD, SD and ES (Figure 1). The patency of the RD was assessed on the orifice of the saccule to the RD based on our previous report [7]. The patencies of the SD and ES were analysed in the same manner by assessing the continuity of their bony grooves [6]. In this study the appearances of the grooves of the RD, SD and ES as not fully recognized was defined as closed and any other state was defined as open to avoid the weak point of the subjective visual evaluation of 3D CT images (Figure 2).
Figure 1.
Figure 1.
3D CT image of the reuniting duct (RD), saccular duct (SD) and endolymphatic sinus (ES) of a healthy volunteer's ear (left), cadaver's ear (upper right), and schematic view (lower right). All these views are left ears. Red arrows show the RD and yellow ...
Figure 2.
Figure 2.
Drawings demonstrating the patency of the reuniting duct (RD), saccular duct (SD) and endolymphatic sinus (ES) on 3D CT images. When otoconia are dislodged into the RD, SD or ES, they lose continuity of the surface of their bony grooves and become vague ...
Additionally, we examined CT images of a cadaver with a small piece of muscle or small amount of calcium carbonate on the bony grooves of SD and ES to assess changes in the CT images, as in our previous report [7].
Statistical analysis
The 62 patients were analyzed in comparison with the normal subjects. The incidence of abnormal images of the bony grooves of those portions in affected ears in MD patients was compared with the non-affected contralateral ears and control volunteer ears and analysed by Yates 2 × 2 chi-squared test.
Results
Findings of RD aspects
Figures 3 and and44 show representative views of different patencies of the RD, SD and ES. Of the ears on the affected side of MD patients (Figures 3A and and4A),4A), 37% (23/62)) had closed RD compared with 9.7% (6/62) of the ears on the non-affected side (Table I). None (0/26) were closed in the normal group (Figures 3B and and4B).4B). There were significant differences between the ears on the affected side of MD patients and normal ears, and between the affected ears and the non-affected ears (p < 0.01) (Figure 5). There was no significant difference between non-affected ears of MD patients and normal ears (p = 0.078).
Figure 3.
Figure 3.
Representative views of the left ear of a patient with Meniere's disease (MD) (A) and a volunteer's healthy ear (B). (A) Although the outline of the bony groove of the reuniting duct (RD) (arrows), saccular duct (SD) and endolymphatic sinus (ES) can be ...
Figure 4.
Figure 4.
Representative views of the right ear of a patient with Meniere's disease (MD) (A) and a volunteer's healthy ear (B). (A) Both the bony grooves of the reuniting duct (RD) and the endolymphatic sinus (ES) are fully occupied by a dense, bony substance and ...
Table I.
Table I.
Status of the reuniting duct (RD), saccular duct (SD) and endolymphatic sinus (ES) in 62 patients with Meniere's disease (MD) and 13 healthy volunteers.
Figure 5.
Figure 5.
Distribution pattern of the reuniting duct (RD) in affected and non-affected ears of patients with Meniere's disease (MD) and healthy ears of volunteers.
Findings of SD aspects
The patencies of the affected and non-affected ears of MD were 51.6% (32/62) and 16.1% (12/62), respectively (Table I). In contrast, all the SDs (26/26) were patent in the healthy ears (Figures 3B and and4B).4B). There were significant differences between the affected ears and healthy ears and between the affected ears and the non-affected ears (p < 0.01). There was a slight but significant difference between the non-affected ears and healthy ears (p = 0.015) (Figure 6).
Figure 6.
Figure 6.
Distribution pattern of the saccular duct (SD) in affected and non-affected ears of patients with Meniere's disease (MD) and healthy ears of volunteers.
Findings of ES aspects
The distribution pattern of the ES resembled that of the SD. The patencies of the affected ears and non-affected ears of MD patients were 64.5% (40/62) and 17.7% (11/62), respectively (Table I). All the ESs (26/26) were patent in the healthy ears (Figures 3B and and4B).4B). There were significant differences between the affected ears and healthy ears and between the affected ears and the non-affected ears (p < 0.01). There was a slight difference between the non-affected ears and healthy ears (p = 0.030) (Figure 7).
Figure 7.
Figure 7.
Distribution pattern of the endolymphatic sinus (ES) in affected and non-affected ears of patients with Meniere's disease (MD) and healthy ears of volunteers.
Findings in the SD and ES of a cadaver treated with CaCO3 and soft tissue fragments
The bony grooves of the SD and ES treated with CaCO3 appeared vague (Figure 8A), but those with muscle fragments were not affected (Figure 8B).
Figure 8.
Figure 8.
3D CT views of a cadaver temporal bone. The bony grooves underlining the saccular duct (SD) and the endolymphatic sinus (ES) treated with CaCO3 (A) appear vague compared with those treated with muscle fragments (B). Note the difference in continuity of ...
Discussion
We could demonstrate differences in visualization or patency of the RD, SD and ES between the affected ears of MD patients and normal ears, suggesting that the RD, SD or ES in MD ears may be partly or entirely occluded compared with healthy ears. The reduced visualization of the RD, SD and ES suggests that these ducts were involved as lesions of MD.
Debris, pathogens or unusual substances in the inner ear can be transported in these narrow ducts and become obstacles to the pathway of longitudinal flow of endolymph resulting in endolymphatic hydrops.
We speculate that a reasonable explanation for this reduced visualization may be an occlusion caused by dislodged otoconia from the saccule. This is based on experimental findings from cadavers showing that the bony groove appears vague when covered with CaCO3 but not when covered with muscle fragments. The data from the present and previous studies [7] suggest that the occlusion may be situated between the saccule and the RD or the SD and the ES.
Saccular otoconia could be dislodged by various causes such as aging as the natural fate, infection, disturbance of blood circulation, trauma, etc., and the dislodged otoconia from the saccule can disperse into the surrounding membranous labyrinth [8,9].
If otoconia fall into such a narrow pathway, the RD to the cochlea or the SD and ES to the endolymphatic duct, they could disturb the endolymphatic flow.
Although saccular otoconia are more susceptible than those of the utricle [10], the incidence of MD patients is not so high in comparison with benign paroxysmal positional vertigo (BPPV) possibly caused by dislodged utricular otoconia [11]. We do not have conclusive data proving this. However, some speculation from our present results may answer this question. The risk of saccular otoconia falling into the RD may not be so high because of its narrowness, even if it is near the saccular otolithic membrane.
The longitudinal endolymph may work to oppose saccular otoconia falling into the RD. On the other hand, the SD and ES are in the path of the anterograde endolymph system. Therefore, the SD (51.6%) and ES (64.5%) may be more occluded than the RD (37%). The character of MD may be due to the rate of occlusion of these narrow ducts.
Histological studies reported that the endolympatic duct (ED) was obstructed with fibrous tissue, basophilic substance or bone in MD [12] and a radiological study also showed narrow and poor development of the ED in MD [13]. The lesions of the ED may have a similar pathology to those of the SD and ES because all these regions are connected as successive membranous pathways, which could support our hypothesis that dislodged saccular otoconia could be a cause of MD. However, more precise investigation of these areas of the human temporal bone in MD is necessary.
Although the non-affected ears in patients with MD showed a similar RD pattern to the affected ears, the similarity was not statistically supported. On the other hand, there were slight differences in the patency of the SD and ES between the non-affected ears and healthy ears. This tendency of occlusion in the SD and ES of the non-affected ears of MD patients suggests that the contralateral non-affected ears may also be challenged but functionally compensated. Earlier acoustic biasing experiments have shown that incipient endolymphatic hydrops may exist in the healthy contralateral ear in MD.
Bilateral engagement of MD varies according to different authors. The longer the duration of the disease the more frequent is the incidence of bilateral disease [14]. In a recent German study where the long-term course of MD was revisited, as many as 35% of subjects suffered from MD in both ears after 10 years and 47% after 20 years [15]. Some studies show a low bilateral incidence (5%) while audiometric low-tone changes occur more frequently (16%) [16]. Also, the modulation depth was found to be significantly reduced in the contralateral non-symptomatic ears of MD patients using low-frequency masking to diagnose endolymphatic hydrops [17]. This has led to the conception that MD is basically a bilateral disease with differing expression in the two ears. In addition, histopathological changes have been described to a large extent in the contralateral temporal bone in patients with unilateral MD [18]. Genetic alterations such as single nucelotide polymorphisms have been described in patients with bilateral MD [19]. The onset of MD has also been found to be earlier when both ears are affected [20]. Although we could not verify signs of bilateralism in our patients with MD in the present unilateral cases, the unilateral group may have included some bilateral cases. This is supported by our 3D CT findings. However, bilaterality of MD must be fully investigated in a future study.
We hypothesize that MD is a pathological condition brought about by saccular dislodged otoconia due to several causes, obstructing the narrow paths of the endolymph, based on the etiology of BPPV caused by dislodged otoconia from the utricle (Figure 9). Although we must investigate many factors of MD and the mechanism of MD attack in the future, the opening of these narrow paths could be one effective therapy for MD.
Figure 9.
Figure 9.
Hypothetical view of blockage of the reuniting duct (RD), saccular duct (SD) and endolymphatic sinus (ES) by dislodged otoconia from the saccule in patients with Meniere's disease (MD). ED, endolymphatic duct; EnS, endolymphatic sac; L, lateral semicircular ...
We evaluated the patency of the RD, SD and ES by 3D CT imaging, reflected by their bony grooves and not the actual ducts and ES. We thus obtained no definitive data on the degree of obstruction using the present 3D CT images.
In addition, the differences on 3D CT images among the various stages of MD that are categorized by degree of hearing deterioration must be investigated in the future.
Acknowledgements
We are indebted to Dr Hiroshi Aradate of J. Morita Corp. for valuable technical assistance.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
References
[1] Yamakawa K. Über die pathologishe Veränderung bei einem Meniere-Kranken. J Otorhinolarngol Soc (Jpn) 1938;44:2310–2.
[2] Hallpike CS, Cairns H. Observation on the pathology of Meniere's syndrome. J Laryngol Otol. 1938;53:625–55.
[3] Kimura RS, Schuknecht HF. Membranous hydrops in the inner ear of the guinea pig after obliteration of the endolymphatic sac. Pract Otorhinolaryngol. 1965;27:343–54.
[4] Schuknecht HF, Rüther A. Blockage of longitudinal flow in the endolymphatic hydrops. Eur Arch Otorhinolaryngol. 1991;248:209–17. [PubMed]
[5] Yamane H, Takayama M, Sunami K, Sakamoto H, Anniko M. Assessment of the reuniting duct by three-dimensional CT rendering. Acta Otolaryngol. 2009;129:1166–8. [PubMed]
[6] Yamane H, Takayama M, Sunami K, Sakamoto H, Imoto T, Anniko M. Visualization and assessment of saccular duct and endolymphatic sinus. Acta Otolaryngol. 2011;131:469–73. [PMC free article] [PubMed]
[7] Yamane H, Takayama M, Sunami K, Sakamoto H, Imoto T, Anniko M. Blockage of reuniting duct in Meniere's disease. Acta Otolaryngol. 2010;130:233–9. [PubMed]
[8] Yamane H, Imoto T, Nakai Y, Igarashi M, Rask-Andersen H. Otoconia degradation. Acta Otolaryngol Suppl. 1984;406:263–70. [PubMed]
[9] Gussen R, Adkins WY., Jr Saccule degeneration and ductus reunions obstruction. Arch Otolaryngol. 1974;99:132–5. [PubMed]
[10] Johnsson L-G. Degenerative changes and anomalies of the vestibular system in man. Laryngoscope. 1971;81:1682–94. [PubMed]
[11] Schuknecht HF. Cupulolithiasis. Arch Otolaryngol. 1969;90:765–78. [PubMed]
[12] Schuknecht HF. Pathology of the ear. 2nd edition. Pennsylvania: Lea & Febiger; 1993. Disorders of unknown or multiple causes; pp. 449–553. p.
[13] Yamamoto E, Mizukaimi C, Isono M, Ohmura M, Hirono Y. Observation of the external aperture of the vestibular duct using three-dimensional surface reconstruction imaging. Laryngoscope. 1991;101:480–3. [PubMed]
[14] Friberg U, Stahle J, Svedberg A. The natural course of Meniere's disease. Acta Otolaryngol Suppl. 1984;406:72–7. [PubMed]
[15] Huppert D, Strupp M, Brandt T. Long-term course of Meniere's disease revisited. Acta Otolaryngol. 2010;130:644–51. [PubMed]
[16] Perez R, Chen JM, Nedzelski JM. The status of the contralateral ear in established unilateral Meniere's disease. Laryngoscope. 2004;114:1373–6. [PubMed]
[17] Mrowinski D, Scholz G, Krompass S, Nubel K. Diagnosis of endolymphatic hydrops by low-frequency masking. Audiol Neurootol. 1997;1:125–34. [PubMed]
[18] Kariya S, Cureoglu S, Fukushima H, Kusunoki T, Schachern PA, Nishizaki K, et al. Histopathologic changes of contralateral human temporal bone in unilateral Meniere's disease. Otol Neurotol. 2007;28:1063–8. [PubMed]
[19] Lopez-Escamez JA, Saenz-Lopez P, Acosta L, Moreno A, Gazquez I, Perez-Garrigues H, et al. Association of a functional polymorphism of PTPN22 encoding a lymphoid protein phosphatase in bilateral Meniere's disease. Laryngoscope. 2010;120:103–7. [PubMed]
[20] Chaves AG, Boari L, Lei Munhoz MS. The outcome of patients with Meniere's disease. Braz J Otorhinolaryngol. 2007;73:346–50. [PubMed]
Thursday, September 11, 2014
Bilateral Vestibular Hypofunction
I know I have experienced many of these symptoms over the years. I always find some reassurance in knowing I'm not completely crazy, so I thought others might appreciate this article I read at Hearing Health Matters . Org.
Bilateral vestibular hypofunction: An interesting problem
By Pathways On September 3, 2014 · Add Comment
Although Pathways primarily focuses on neuroaudiology and CAPD, we will occasionally have articles on closely related issues such as the one below reviewing bilateral vestibular hypofunction, which is not only a peripheral, but also a central vestibular problem.
Bilateral vestibular hypofunction: An interesting problem
Stephanie A. Waryasz, B.S.
University of Connecticut
Bilateral vestibular hypofunction (BVH) is a disorder that creates reduced or absent function on both sides of the vestibular system, as its name implies. The disorder is characterized by general imbalance, especially during movement, movement-induced dizziness and movement-induced vision instability, also known as oscillopsia. Such symptoms are usually debilitating and greatly affects one’s ability to participate in activities daily living such as walking, driving, and reading, which can consequently impact a person’s employability, social life, and emotional well-being (Braswell & Rine, 2006; Herdman, Hall, Schubert, Das, & Tusa, 2007; Guinand, Pijnenburg, Janssen, & Kingma, 2012; Ward, Agrawal, Hoffman, Carey, & Della Santina, 2013).
BVH has also been associated with certain cognitive deficits such as spatial learning and spatial memory deficits due to a 17% reduction in hippocampal volume and decreased metabolic activity within the anterior hippocampus (McCall & Yates, 2011). From data analysis of the 2008 US National Health Interview Survey, it is believed that severe to profound BVH affects upwards of 28 in 100,000 adults in the United States or 64,046 Americans (Ward et al., 2013). These prevalence estimates are considered to be conservative, as people with confounding neurological and visual conditions, which could comorbidly exist with BVH, were excluded from the criteria used by Ward et al. (2013). Furthermore, Ward et al. (2013) used strict criteria to estimate the prevalence of BVH based on affirmations to case history questions that are known symptoms of severe to profound BVH. By extrapolating United States estimates, Ward et al. (2013) suggest that 1.8 million people worldwide could be affected by BVH, with the caveat that prevalence of BVH may vary geographically based on medical treatments such as the use of vestibulotoxic drugs.
Etiology
The most common etiology of BVH is systemic vestibulotoxicity from aminoglycoside antibiotics, specifically gentamicin and streptomycin (Schubert & Minor, 2004; Ward et al., 2013). These types of antibiotics are known for more selectively damaging vestibular hair cells while oftentimes leaving auditory hair cells unharmed, depending on the medication dosage administered (Schubert & Minor, 2004). The incidence of BVH ranges between 3%-4% when a patient is treated with gentamicin (Schubert & Minor, 2004). The incidence of BVH increases to between 12.5% and 30% for patients treated with both gentamicin and renal dialysis simultaneously (Schubert & Minor, 2004). These figures further emphasize the vulnerability and susceptibility of vestibular hair cells to drug-induced toxicity effects.
Less common etiologies of BVH include meningitis, head trauma, transient ischemic episodes of vessels supplying the vestibular system, bilateral tumors on cranial nerve VIII including vestibular schwannoma tumors, and sequential cases of unilateral vestibular neuronitis (Schubert & Minor, 2004). Ménière’s disease, encephalitis, labyrinthitis, autoimmune disease, and iatrogenic damage due to surgical procedures such as cochlear implantation have also been cited as potential etiologies of BVH (McCall & Yates, 2011; Ward et al., 2013;).
Pathological Process
The pathological process of BVH suggests a deficit in the vestibular system that results in inadequate compensatory eye movements during head movement that creates a slip of visual targets across the retina (McCall & Yates, 2011; Schubert & Minor, 2004), which consequently yields oscillopsia, one of the critical symptoms of BVH for differential diagnosis (Ward et al., 2013). This deficit makes it impossible for the vestibulo-ocular reflex (VOR) to respond appropriately. The VOR is responsible for generating compensatory eye movements that correspond to opposite head movements, ultimately stabilizing vision and gaze (Guinand et al., 2012; Vital et al., 2010). VOR deficits contribute to issues with gait, postural instability, and disequilibrium upon movement (Schubert & Minor, 2004). Such deficits are enhanced with an increase the velocity of head movements (Guinand et al., 2012; Vital et al., 2010).
Clinical Assessment
Clinical tests often used to diagnose BVH include the head thrust test to examine the VOR (Minor, 1998; McCall & Yates, 2011), various Romberg stances and tandem walks to view static imbalance (Minor, 1998; McCall & Yates, 2011), rapid full-body turns or external perturbations such as light shoves can help to assess dynamic imbalance (Minor, 1998; McCall & Yates, 2011), optokinetic testing presents with a severe reduction in nystagmus or no nystagmus with BVH (McCall & Yates, 2011), and caloric testing, which can identify reduced gaze stabilization of the VOR in the low frequency range (Vital et al., 2010). Due to the symptomology of BVH indicating severe deficits in gaze stabilization especially with movement, perhaps one of the best tests to assess BVH is the dynamic visual acuity test (Guinand et al., 2012; Herdman et al., 2007; Herdman et al., 1998; Schubert & Minor, 2004; Vital et al., 2010).
The dynamic visual acuity test assesses visual acuity while the head is in motion, which is typically self-generated (Schubert & Minor, 2004). Additionally, it examines the capacity of the VOR to maintain gaze stability during such head movement (Minor, 1998). Many different versions of this test exist, ranging from bedside to computerized to using scleral search coils to performing functional assessment on a treadmill (Guinand et al., 2012; Herdman et al., 2007; Herdman et al., 1998; Minor, 1998; Schubert & Minor, 2004; Vital et al., 2010). The bedside test can be performed informally by having the patient read a newspaper with the head remaining still, then having the patient try to continue reading while moving their head from side to side at a rate of about 2 cycles per second (Minor, 1998).
A more formal option would be to utilize computerized dynamic visual acuity testing. Herdman and colleagues (1998 & 2007) researched a method of calculating dynamic visual acuity by counting the total number of errors in identifying the orientation of the computerized optotype “E” while the subject’s head was moved predictability to the right or to the left. This quantity was then subtracted from the subject’s static visual acuity score to yield their dynamic visual acuity score. Herdman et al. (1998) reported 96.2% sensitivity, 100% specificity, and 97.5% overall accuracy in using this test to identify subjects with BVH in comparison to normal control subjects. The capacity of this test to distinguish between unilateral vestibular hypofunction (UVH) and BVH was also noted.
Dynamic Visual Acuity Testing Research
Vital et al. (2010) created a different computerized dynamic visual acuity test to assess peripheral vestibular function. This study assessed the subject’s ability to compute differences between visual acuity in static and dynamic conditions during active and passive horizontal head rotations at velocities exceeding 100°/sec and exceeding 150°/sec, respectively. Velocities were measured with a Sparkfun velocity sensory fixed to a headset worn by each subject. An active head rotation was generated by the subject’s participation in active movements. The passive head rotations were delivered by the examiner at random intervals by holding the head laterally on both sides outside of the subject’s visual field. To obtain the visual acuity level for each condition, the subject needed to identify the orientation of Landolt rings, a common optotype used for vision tests that looks like the letter “C”. Landolt rings were presented in sets of five for each visual acuity level.
The test terminated after the subject was unable to correctly identify at least three Landolt ring orientations at a given visual acuity level. To help with fixation during head rotation, a small dot was placed on the center of the monitor, which was only extinguished immediately before a Landolt ring was presented.
Vital and colleagues (2010) also verified their computerized results with quantitative horizontal head impulse testing (qHIT) with scleral search coils around the cornea of the right eye. The researchers noted that this test was clinically useful in identifying semicircular canal function in the high frequency range, which was reported to be more important in the assessment of gaze stabilization of the VOR.
The benefit of this test is that it can be easily administered within the office excluding the scleral search coil verification. However, the researchers warn that the examiner should be experienced with this test before utilizing it and the patient should be trained to minimize learning curve effects. The sensitivity of this test for identifying BVH was reported to be 100% and the specificity was reported to be 94% when performing passive rotation with the head velocity exceeding 150°/sec.
Guinand et al. (2012) created a unique type of dynamic visual acuity test that assessed functional dynamic visual acuity while on a treadmill. The difference between static and dynamic visual acuity was computed to determine the subject’s total dynamic visual acuity. Subjects were asked to read Sloan letters placed 2.8 meters away starting at the 20/25 visual acuity line. The visual acuity value of the most finite visual acuity with at least three correct responses was recorded as the acuity level for that test. Dynamic visual acuity testing was performed at three different velocities on a treadmill: 2 km/hr, 4 km/hr, and 6 km/hr. Researchers reported 97% sensitivity to identifying BVH when the visual acuity was measured at all three velocities. The sensitivity decreased to 76% if only 2 km/hr was recorded in the dynamic condition and 84% sensitivity if only 4 km/hr was recorded. If the dynamic testing was conducted at both 2 and 4 km/hr the sensitivity increased to 95%. Specificity was not reported by Guinand and colleagues (2012).
The benefits of this type of testing include its simple and cost-effective procedure that could be performed in less than 10 minutes without prior training for the patient or the test administrator. The main drawback to this test is that it requires a treadmill, which may not be accessible to all clinicians who would like to assess dynamic visual acuity. The researchers also noted that this test may be clinically useful in assessing functional outcomes of a vestibular training protocol. Additionally, this test could be used to assess candidacy for treatment options such as vestibular prosthesis implantation and post-surgical functional assessment. A summary of the three previously reviewed types of dynamic visual assessment tests (Guinand et al., 2012; Herdman et al., 2007; Herdman et al., 1998; Vital et al., 2010) can be seen in the Table below.
Table: A review of different dynamic visual acuity (DVA) assessment measures to identify bilateral vestibular hypofunction (BVH) with reported benefits, drawbacks, and clinical utility of each protocol from supporting research.
Table: A review of different dynamic visual acuity (DVA) assessment measures to identify bilateral vestibular hypofunction (BVH) with reported benefits, drawbacks, and clinical utility of each protocol from supporting research.
Due to the disease process of BVH, spontaneous recovery is rare (McCall & Yates, 2011). Therefore, techniques are necessary to provide relief to patients dealing with the debilitating effects of this disorder. There is currently no standardized treatment for BVH; however, research has shown potential for therapies and procedures to help manage BVH.
A review by McCall and Yates (2011) discusses vestibular physical therapy as a treatment option for BVH that has been shown to improve dynamic gait stability in addition to dynamic visual acuity in approximately 50% of patients. This figure suggests that half of the BVH patient population may already have innate compensatory processes that render such treatment fruitless. Sensory substitution has been highlighted as an alternative treatment method for BVH. This technique offers information typically processed by the vestibular system in an alternate modality such as visual, auditory, or tactile. The use of visual cues, auditory cues, head-mounted vibrotactile devices, or electrotactile feedback to the tongue are examples of alternate means of providing sensory feedback for the patient. Current research shows promise of a vestibular prosthesis in humans, which will function similarly to a cochlear implant in that an electrode array will be inserted into the semicircular canal. Conversely, the electrical stimulation for the vestibular prosthesis would be controlled by an accelerometer to detect head motion. It is believed that this stimulation will elicit appropriate eye movement compensation.
In summation, BVH is a debilitating disorder affecting both peripheral and central vestibular systems that most commonly yields postural instability, gait deficits, and oscillopsia due to a slip of the visual target across the retina interfering with the VOR (Herdman et al., 2007; Guinand et al., 2012; Ward et al., 2013). Central basis for BVH would likely also have central auditory findings, as these pathways are very close in proximity to each other, especially in the brainstem. The most commonly reported etiology of BVH is vestibulotoxicity due to use of aminoglycoside antibiotics (Schubert & Minor, 2004; Ward et al., 2013). This disorder can be identified through numerous tests, with dynamic visual acuity testing being one of the most clinically useful (Guinand et al., 2012; Herdman et al., 2007; Herdman et al., 1998; Schubert & Minor, 2004; Vital et al., 2010). Treatment options are widely varied for this disorder and should be individualized to meet the specific needs of the patient.
Stephanie Waryasz is a third year doctoral student of Audiology at the University of Connecticut. She completed her undergraduate Bachelor of Science degree in Communication Disorders at Southern Connecticut State University graduating with departmental honors. At Southern Connecticut State University, she completed an undergraduate thesis on the topic of mild traumatic brain injury and the treatment of blast victims in VA facilities returning from the Iraq and Afghanistan wars. Currently, Stephanie is examining the effects of sports-related concussion on auditory processing in university athletes for her Au.D. capstone research project at U Conn. Stephanie also enjoys volunteering for the Healthy Hearing Initiative at the Special Olympics in New Haven, CT and for Hear Here Hartford in Wethersfield, CT – an organization that helps to empower teens and young adults with hearing loss.
References
Braswell, J., & Rine, R. M. (2006). Evidence that vestibular hypofunction affects reading acuity in children. International Journal of Pediatric Otorhinolaryngology, 70, 1957–1965.
Guinand, N., Pijnenburg, M., Janssen, M., & Kingma, H. (2012). Visual acuity while walking and oscillopsia severity in healthy subjects and patients with unilateral and bilateral vestibular function loss. Arch Otolaryngol Head Neck Surg, 138(3), 301–306.
Herdman, S. J., Hall, C. D., Schubert, M. C., Das, V. E., & Tusa, R. J. (2007). Recovery of dynamic visual acuity in bilateral vestibular hypofunction. Arch Otolaryngol Head Neck Surg, 133, 383–389.
Herdman, S. J., Tusa, R. J., Blatt, P., Suzuki, A., Venuto, P., & Roberts, D. (1998). Computerized dynamic visual acuity test in the assessment of vestibular deficits. Am J Otol, 19, 790–796.
McCall, A. A., & Yates, B. J. (2011). Compensation following bilateral vestibular damage. Frontiers in Neurology, 2, 1–13.
Minor, L. B. (1998). Gentamicin-induced bilateral vestibular hypofunction. JAMA, 279(7), 541–544.
Schubert, M. C., & Minor, L. B. (2004). Vestibulo-ocular physiology underlying vestibular hypofunction. Physical Therapy, 84(4), 373–385.
Vital, D., Hegemann, S. C. A., Straumann, D., Bergamin, O., Bockisch, C. J., Angehrn, D., … Probst, R. (2010). A new dynamic visual acuity test to assess peripheral vestibular hypofunction. Arch Otolaryngol Head Neck Surg, 136(7), 686–691.
Ward, B. K., Agrawal, Y., Hoffman, H. J., Carey, J. P., & Della Santina, C. C. (2013).
Prevalence and impact of bilateral vestibular hypofunction: Results from the 2008 US National Health Interview Survey. JAMA Otolaryngology-Head & Neck Surgery, 139(8), 803–810.
This article is a publication of the Pathways Society. Copyright Hearing Health & Technology Matters. All rights reserved, 2014. For permission to republish this article, please contact Dr. Frank Musiek.
Bilateral vestibular hypofunction: An interesting problem
By Pathways On September 3, 2014 · Add Comment
Although Pathways primarily focuses on neuroaudiology and CAPD, we will occasionally have articles on closely related issues such as the one below reviewing bilateral vestibular hypofunction, which is not only a peripheral, but also a central vestibular problem.
Bilateral vestibular hypofunction: An interesting problem
Stephanie A. Waryasz, B.S.
University of Connecticut
Bilateral vestibular hypofunction (BVH) is a disorder that creates reduced or absent function on both sides of the vestibular system, as its name implies. The disorder is characterized by general imbalance, especially during movement, movement-induced dizziness and movement-induced vision instability, also known as oscillopsia. Such symptoms are usually debilitating and greatly affects one’s ability to participate in activities daily living such as walking, driving, and reading, which can consequently impact a person’s employability, social life, and emotional well-being (Braswell & Rine, 2006; Herdman, Hall, Schubert, Das, & Tusa, 2007; Guinand, Pijnenburg, Janssen, & Kingma, 2012; Ward, Agrawal, Hoffman, Carey, & Della Santina, 2013).
BVH has also been associated with certain cognitive deficits such as spatial learning and spatial memory deficits due to a 17% reduction in hippocampal volume and decreased metabolic activity within the anterior hippocampus (McCall & Yates, 2011). From data analysis of the 2008 US National Health Interview Survey, it is believed that severe to profound BVH affects upwards of 28 in 100,000 adults in the United States or 64,046 Americans (Ward et al., 2013). These prevalence estimates are considered to be conservative, as people with confounding neurological and visual conditions, which could comorbidly exist with BVH, were excluded from the criteria used by Ward et al. (2013). Furthermore, Ward et al. (2013) used strict criteria to estimate the prevalence of BVH based on affirmations to case history questions that are known symptoms of severe to profound BVH. By extrapolating United States estimates, Ward et al. (2013) suggest that 1.8 million people worldwide could be affected by BVH, with the caveat that prevalence of BVH may vary geographically based on medical treatments such as the use of vestibulotoxic drugs.
Etiology
The most common etiology of BVH is systemic vestibulotoxicity from aminoglycoside antibiotics, specifically gentamicin and streptomycin (Schubert & Minor, 2004; Ward et al., 2013). These types of antibiotics are known for more selectively damaging vestibular hair cells while oftentimes leaving auditory hair cells unharmed, depending on the medication dosage administered (Schubert & Minor, 2004). The incidence of BVH ranges between 3%-4% when a patient is treated with gentamicin (Schubert & Minor, 2004). The incidence of BVH increases to between 12.5% and 30% for patients treated with both gentamicin and renal dialysis simultaneously (Schubert & Minor, 2004). These figures further emphasize the vulnerability and susceptibility of vestibular hair cells to drug-induced toxicity effects.
Less common etiologies of BVH include meningitis, head trauma, transient ischemic episodes of vessels supplying the vestibular system, bilateral tumors on cranial nerve VIII including vestibular schwannoma tumors, and sequential cases of unilateral vestibular neuronitis (Schubert & Minor, 2004). Ménière’s disease, encephalitis, labyrinthitis, autoimmune disease, and iatrogenic damage due to surgical procedures such as cochlear implantation have also been cited as potential etiologies of BVH (McCall & Yates, 2011; Ward et al., 2013;).
Pathological Process
The pathological process of BVH suggests a deficit in the vestibular system that results in inadequate compensatory eye movements during head movement that creates a slip of visual targets across the retina (McCall & Yates, 2011; Schubert & Minor, 2004), which consequently yields oscillopsia, one of the critical symptoms of BVH for differential diagnosis (Ward et al., 2013). This deficit makes it impossible for the vestibulo-ocular reflex (VOR) to respond appropriately. The VOR is responsible for generating compensatory eye movements that correspond to opposite head movements, ultimately stabilizing vision and gaze (Guinand et al., 2012; Vital et al., 2010). VOR deficits contribute to issues with gait, postural instability, and disequilibrium upon movement (Schubert & Minor, 2004). Such deficits are enhanced with an increase the velocity of head movements (Guinand et al., 2012; Vital et al., 2010).
Clinical Assessment
Clinical tests often used to diagnose BVH include the head thrust test to examine the VOR (Minor, 1998; McCall & Yates, 2011), various Romberg stances and tandem walks to view static imbalance (Minor, 1998; McCall & Yates, 2011), rapid full-body turns or external perturbations such as light shoves can help to assess dynamic imbalance (Minor, 1998; McCall & Yates, 2011), optokinetic testing presents with a severe reduction in nystagmus or no nystagmus with BVH (McCall & Yates, 2011), and caloric testing, which can identify reduced gaze stabilization of the VOR in the low frequency range (Vital et al., 2010). Due to the symptomology of BVH indicating severe deficits in gaze stabilization especially with movement, perhaps one of the best tests to assess BVH is the dynamic visual acuity test (Guinand et al., 2012; Herdman et al., 2007; Herdman et al., 1998; Schubert & Minor, 2004; Vital et al., 2010).
The dynamic visual acuity test assesses visual acuity while the head is in motion, which is typically self-generated (Schubert & Minor, 2004). Additionally, it examines the capacity of the VOR to maintain gaze stability during such head movement (Minor, 1998). Many different versions of this test exist, ranging from bedside to computerized to using scleral search coils to performing functional assessment on a treadmill (Guinand et al., 2012; Herdman et al., 2007; Herdman et al., 1998; Minor, 1998; Schubert & Minor, 2004; Vital et al., 2010). The bedside test can be performed informally by having the patient read a newspaper with the head remaining still, then having the patient try to continue reading while moving their head from side to side at a rate of about 2 cycles per second (Minor, 1998).
A more formal option would be to utilize computerized dynamic visual acuity testing. Herdman and colleagues (1998 & 2007) researched a method of calculating dynamic visual acuity by counting the total number of errors in identifying the orientation of the computerized optotype “E” while the subject’s head was moved predictability to the right or to the left. This quantity was then subtracted from the subject’s static visual acuity score to yield their dynamic visual acuity score. Herdman et al. (1998) reported 96.2% sensitivity, 100% specificity, and 97.5% overall accuracy in using this test to identify subjects with BVH in comparison to normal control subjects. The capacity of this test to distinguish between unilateral vestibular hypofunction (UVH) and BVH was also noted.
Dynamic Visual Acuity Testing Research
Vital et al. (2010) created a different computerized dynamic visual acuity test to assess peripheral vestibular function. This study assessed the subject’s ability to compute differences between visual acuity in static and dynamic conditions during active and passive horizontal head rotations at velocities exceeding 100°/sec and exceeding 150°/sec, respectively. Velocities were measured with a Sparkfun velocity sensory fixed to a headset worn by each subject. An active head rotation was generated by the subject’s participation in active movements. The passive head rotations were delivered by the examiner at random intervals by holding the head laterally on both sides outside of the subject’s visual field. To obtain the visual acuity level for each condition, the subject needed to identify the orientation of Landolt rings, a common optotype used for vision tests that looks like the letter “C”. Landolt rings were presented in sets of five for each visual acuity level.
The test terminated after the subject was unable to correctly identify at least three Landolt ring orientations at a given visual acuity level. To help with fixation during head rotation, a small dot was placed on the center of the monitor, which was only extinguished immediately before a Landolt ring was presented.
Vital and colleagues (2010) also verified their computerized results with quantitative horizontal head impulse testing (qHIT) with scleral search coils around the cornea of the right eye. The researchers noted that this test was clinically useful in identifying semicircular canal function in the high frequency range, which was reported to be more important in the assessment of gaze stabilization of the VOR.
The benefit of this test is that it can be easily administered within the office excluding the scleral search coil verification. However, the researchers warn that the examiner should be experienced with this test before utilizing it and the patient should be trained to minimize learning curve effects. The sensitivity of this test for identifying BVH was reported to be 100% and the specificity was reported to be 94% when performing passive rotation with the head velocity exceeding 150°/sec.
Guinand et al. (2012) created a unique type of dynamic visual acuity test that assessed functional dynamic visual acuity while on a treadmill. The difference between static and dynamic visual acuity was computed to determine the subject’s total dynamic visual acuity. Subjects were asked to read Sloan letters placed 2.8 meters away starting at the 20/25 visual acuity line. The visual acuity value of the most finite visual acuity with at least three correct responses was recorded as the acuity level for that test. Dynamic visual acuity testing was performed at three different velocities on a treadmill: 2 km/hr, 4 km/hr, and 6 km/hr. Researchers reported 97% sensitivity to identifying BVH when the visual acuity was measured at all three velocities. The sensitivity decreased to 76% if only 2 km/hr was recorded in the dynamic condition and 84% sensitivity if only 4 km/hr was recorded. If the dynamic testing was conducted at both 2 and 4 km/hr the sensitivity increased to 95%. Specificity was not reported by Guinand and colleagues (2012).
The benefits of this type of testing include its simple and cost-effective procedure that could be performed in less than 10 minutes without prior training for the patient or the test administrator. The main drawback to this test is that it requires a treadmill, which may not be accessible to all clinicians who would like to assess dynamic visual acuity. The researchers also noted that this test may be clinically useful in assessing functional outcomes of a vestibular training protocol. Additionally, this test could be used to assess candidacy for treatment options such as vestibular prosthesis implantation and post-surgical functional assessment. A summary of the three previously reviewed types of dynamic visual assessment tests (Guinand et al., 2012; Herdman et al., 2007; Herdman et al., 1998; Vital et al., 2010) can be seen in the Table below.
Table: A review of different dynamic visual acuity (DVA) assessment measures to identify bilateral vestibular hypofunction (BVH) with reported benefits, drawbacks, and clinical utility of each protocol from supporting research.
Table: A review of different dynamic visual acuity (DVA) assessment measures to identify bilateral vestibular hypofunction (BVH) with reported benefits, drawbacks, and clinical utility of each protocol from supporting research.
Due to the disease process of BVH, spontaneous recovery is rare (McCall & Yates, 2011). Therefore, techniques are necessary to provide relief to patients dealing with the debilitating effects of this disorder. There is currently no standardized treatment for BVH; however, research has shown potential for therapies and procedures to help manage BVH.
A review by McCall and Yates (2011) discusses vestibular physical therapy as a treatment option for BVH that has been shown to improve dynamic gait stability in addition to dynamic visual acuity in approximately 50% of patients. This figure suggests that half of the BVH patient population may already have innate compensatory processes that render such treatment fruitless. Sensory substitution has been highlighted as an alternative treatment method for BVH. This technique offers information typically processed by the vestibular system in an alternate modality such as visual, auditory, or tactile. The use of visual cues, auditory cues, head-mounted vibrotactile devices, or electrotactile feedback to the tongue are examples of alternate means of providing sensory feedback for the patient. Current research shows promise of a vestibular prosthesis in humans, which will function similarly to a cochlear implant in that an electrode array will be inserted into the semicircular canal. Conversely, the electrical stimulation for the vestibular prosthesis would be controlled by an accelerometer to detect head motion. It is believed that this stimulation will elicit appropriate eye movement compensation.
In summation, BVH is a debilitating disorder affecting both peripheral and central vestibular systems that most commonly yields postural instability, gait deficits, and oscillopsia due to a slip of the visual target across the retina interfering with the VOR (Herdman et al., 2007; Guinand et al., 2012; Ward et al., 2013). Central basis for BVH would likely also have central auditory findings, as these pathways are very close in proximity to each other, especially in the brainstem. The most commonly reported etiology of BVH is vestibulotoxicity due to use of aminoglycoside antibiotics (Schubert & Minor, 2004; Ward et al., 2013). This disorder can be identified through numerous tests, with dynamic visual acuity testing being one of the most clinically useful (Guinand et al., 2012; Herdman et al., 2007; Herdman et al., 1998; Schubert & Minor, 2004; Vital et al., 2010). Treatment options are widely varied for this disorder and should be individualized to meet the specific needs of the patient.
Stephanie Waryasz is a third year doctoral student of Audiology at the University of Connecticut. She completed her undergraduate Bachelor of Science degree in Communication Disorders at Southern Connecticut State University graduating with departmental honors. At Southern Connecticut State University, she completed an undergraduate thesis on the topic of mild traumatic brain injury and the treatment of blast victims in VA facilities returning from the Iraq and Afghanistan wars. Currently, Stephanie is examining the effects of sports-related concussion on auditory processing in university athletes for her Au.D. capstone research project at U Conn. Stephanie also enjoys volunteering for the Healthy Hearing Initiative at the Special Olympics in New Haven, CT and for Hear Here Hartford in Wethersfield, CT – an organization that helps to empower teens and young adults with hearing loss.
References
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This article is a publication of the Pathways Society. Copyright Hearing Health & Technology Matters. All rights reserved, 2014. For permission to republish this article, please contact Dr. Frank Musiek.
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