Vestibular evoked myogenic potentials in delayed endolymphatic hydrops

OBJECTIVE/HYPOTHESIS: Vestibular evoked myogenic potential (VEMP) has become an established test to explore the sacculo-collic reflex. The study aims to investigate the VEMPs in cases of delayed endolymphatic hydrops because greatly dilated saccule was observed in histopathological specimens of delayed endolymphatic hydrops. STUDY DESIGN: Prospective study. METHODS: Twenty patients with delayed endolymphatic hydrops were subjected to pure-tone audiometry, caloric testing, and VEMP test. Delayed VEMP was defined as the latency of peak I exceeding 22.6 milliseconds or of peak II exceeding 33.1 milliseconds. Interaural amplitude difference over the sum of amplitudes of both ears was measured, and when the ratio exceeded 0.36, it was identified as augmented VEMP or depressed VEMP depending on whether the amplitude of the lesioned side was greater or less than the opposite side. RESULTS: The VEMP test revealed that 9 patients (45%) were normal, 6 (30%) exhibited absent VEMPs, and 5 (25%) displayed abnormal VEMPs, including delayed VEMPs in 2, depressed VEMPs in 2, and augmented VEMPs in 1. The caloric test indicated that 9 (47%) of the 19 ears exhibited normal caloric response, whereas 10 ears displayed abnormal caloric responses including canal paresis in 8 and absent caloric response in 2. Six ears had preserved both the caloric response and the VEMPs, whereas no ear demonstrated both absent caloric response and absent VEMPs. CONCLUSIONS: The residual caloric as well as saccular functions after ear insult may determine whether delayed endolymphatic hydrops will occur. These findings suggest that patients with sudden deafness or juvenile unilateral total deafness should undergo caloric testing and VEMP test to predict the occurrence of delayed endolymphatic hydrops in the future.     

Glycerol pure tone audiometry and glycerol vestibular evoked myogenic potential: representing specific status of endolymphatic hydrops in the inner ear

This prospective study attempts to explore the effect of glycerol on vestibular evoked myogenic potential (VEMP) in patients with definite unilateral Meniere’s disease (MD) and to investigate whether the test reflects different pathologic states of endolymphatic hydrops (EH) in the inner ear by comparing the results of glycerol pure tone audiometry (PTA). Twenty-eight patients with definite unilateral MD were studied. As a control group, 11 patients with vestibular neuritis were selected. Sixteen ears of normal volunteers were enrolled to acquire normal range of the test. Each MD patient underwent glycerol testing measure with both conventional PTA and VEMP testing. Eleven vestibular neuritis patients also underwent glycerol-VEMP testing. The difference ratio was adopted to compare the changes in p1-n1 amplitude and latency of VEMP after the administration of glycerol (1.3 g/kg). Significant changes in the VEMP wave after the glycerol loading were seen in amplitude, but not in latency with MD patients. On the affected side, the amplitude of the p1-n1 biphasic wave significantly increased in 11 of 28 (39.3%) ears and decreased in 2 (7.1%) ears. On the unaffected side, 5 (17.9%) ears showed significant increase in amplitude. Significant changes in PTA were noted after administration of glycerol in 14 of 28 (50%) patients with MD. However, there was no statistically significant correlation between the test results. Glycerol administration had no significant effect on VEMP in patients with vestibular neuritis. The amplitude of VEMP in some patients with MD was increased, but the latency was not influenced by oral administration of glycerol. The severity of EH appears to vary in different parts of the inner ear. Glycerol-VEMP test results in patients with vestibular neuritis suggest that the VEMP reflects potential abnormality in the sacculocollic pathway, while glycerol-VEMP identifies the existence of EH in the saccule. VEMP and PTA after glycerol administration provide potential status of MD.     

迟发性膜迷路积水的诊断

目的：探讨迟发性膜迷路积水（DEH）的诊断手段及意义。方法：15例DEH患者,分别行纯音听阈及耳蜗电图检查、前庭双温试验和前庭诱发的肌源性电位检查（VEMP）,用以诊断及判断DEH的侧别和病变累及范围。结果：15例患者均为中～重度以上感音神经性聋。积水与听力下降同侧10例,对侧4例,双侧1例。水平半规管和球囊均有积水5例,水平半规管积水6例,球囊积水2例。VEMP异常者7例,其中1例患侧p13-n23振幅消失,2例p13潜伏期延长,4例患侧p13-n23低振幅。结论：DEH的诊断除了纯音测听外,耳蜗电图检查、前庭双温试验和VEMP检查是重要的实验室检查,应列为诊断常规。     

Vestibular evoked myogenic potentials of undiagnosed dizziness

OBJECTIVE: Recording of vestibular evoked myogenic potentials (VEMP) can facilitate the evaluation of otolith function. The dizziness caused by otolith lesions is not completely understood. To clarify which symptoms of dizziness originate from the otolith organs, we examined the relationship between symptoms and VEMP results in patients with undiagnosed dizziness. METHODS: The subjects were 18 patients with undiagnosed dizziness aged less than 40 years who underwent VEMP examination. The VEMP results were evaluated using the interaural ratio of p13-n23 amplitude. RESULTS: Abnormal VEMP results were obtained in five of seven patients who experienced a sensation of falling (p=0.013), in none of the three patients who experienced a swaying sensation (p>0.05), and in one of eight patients who experienced a floating sensation (p>0.05). Five of six patients with abnormal VEMP results complained of disequilibrium lasting a few seconds. CONCLUSIONS: Dizziness with a sensation of falling lasting for a few seconds was related to abnormal VEMP results, suggesting that it resulted from saccular dysfunction. VEMP examination may be considered a useful modality in the diagnosis of dizziness of unknown origin.     

Vestibular evoked myogenic potentials and glycerol testing

OBJECTIVES/HYPOTHESIS: The objective was to evaluate dizziness as the first symptom of endolymphatic hydrops, which could provide valuable information on the initial stages of endolymphatic hydrops development. STUDY DESIGN: The present investigation was specifically designed to establish whether a combination of the traditional glycerol test and the vestibular evoked myogenic potential (VEMP) glycerol test is capable of diagnosing endolymphatic hydrops early and to identify potential Meniere's disease. The study was limited to patients who complained of dizziness as their only vestibular symptom. METHODS: Thirty-eight consecutive patients with dizziness who had received no treatment were investigated. Each patient underwent glycerol testing measured with both conventional pure-tone audiometry and vestibular evoked myogenic potential testing. For the vestibular evoked myogenic potential glycerol test, an increase of more than 20% in both latency and amplitude after glycerol intake was considered an improvement.RESULTS In one patient, the reappearance of the vestibular evoked myogenic potentials was observed. In another six patients, there was an increase in the vestibular evoked myogenic potential amplitudes, unilaterally in four cases and bilaterally in two. One patient showed a bilateral improvement in amplitude and an unilateral amelioration in latency. CONCLUSION: The assumption of saccular dilation as a sign of early Meniere's disease was not supported by the literature, which considered saccular hydrops as the final progression of the dilation of the endolymphatic compartments into the cochlea. These data seem to indicate that in our patients a saccular dysfunction rather than an early saccular hydrops has been documented, confirming vestibular evoked myogenic potential testing as an intriguing diagnostic option for a lesion of this structure. The vestibular evoked myogenic potential glycerol test proved capable of identifying dysfunctions of the saccule that were not otherwise detectable by the routine methods. Therefore, the vestibular evoked myogenic potential glycerol test should be considered as an additional method of diagnosis in patients with vertigo or dizziness.     

Vestibular evoked myogenic potentials in Behcet’s disease

The aim of this study was to investigate vestibular evoked myogenic potentials (VEMPs) and their clinical significance in Behcet’s disease. Twenty-six patients with Behcet’s disease and 25 healthy volunteers were evaluated for pure tone audiometry, caloric response, and VEMPs. Sensorineural hearing loss was found in 53.8% of patients with Behcet’s disease, which was significantly higher than controls. Four patients had canal paresis, but no controls; this difference was not significant. Although VEMP recordings were elicited in all study subjects, mean p13 and n23 latencies were prolonged in Behcet’s patients compared with controls. Seven patients had delayed VEMP responses. There were no correlations regarding p13 values and age, duration or activity of disease, vertigo, or sensorineural hearing loss. The results of this preliminary study suggest an association between delayed VEMP responses and Behcet’s disease. Further research with large samples is needed to confirm that VEMP testing is useful to diagnose and follow vestibular dysfunction in Behcet’s disease. This study has been presented at the XXIX. National Otolaryngology Head and Neck Surgery Congress, Antalya, Turkey, May 26–31, 2007. This study was supported by a Baskent University Research Foundation grant (Project No. KA04/188).     

Vestibular evoked myogenic potentials of haemodialysed patients with end stage renal disease

End stage renal disease (ESRD) can cause malfunction of multiple organs, including auditory and vestibular systems. During recent years, a significant amount of research has demonstrated the direct involvement of the otolith organs in stabilizing body and gaze which led to the development of specific functional tests. Stable gaze and body are more important in patients with ESRD, as they have an increased risk of bone fracture. The aim of this study was to investigate saccule and related neural pathways in haemodialysed patients with chronic renal failure. Twenty patients (40 ears) with ESRD were tested for vestibular evoked myogenic potentials (VEMP). Results were compared with those of 16 healthy controls (32 ears). VEMP response was significantly different between subjects and patients with ESRD. There was a significant difference between the presence and absence of VEMP waves in ESRD patient when compared with creatinine levels.     

Comparison of furosemide-loading cervical vestibular-evoked myogenic potentials with magnetic resonance imaging for the evaluation of endolymphatic hydrops

Abstract

Background

Furosemide-loading cervical vestibular-evoked myogenic potential (FVEMP), in which vestibular function is improved via diuretics-induced dehydration, can be used to estimate the presence of endolymphatic hydrops, one characteristic of Menière’s disease. Inner ear magnetic resonance imaging (MRI) can also reveal endolymphatic hydrops.

Aims/Objective: This study aimed to compare and confirm the usefulness of these two examination methods for the diagnosis of Menière’s disease.     

前庭诱发肌源性电位的正常人群观察

目的:观察我国正常青年人群中前庭诱发肌源性电位(VEMP)出现的阳性率及各项参数指标。方法:选取52例(男31例,女21例)21~22岁正常健康人群,以短声为刺激声,单耳给声,同侧胸锁乳突肌(SCM)记录。结果:47例2耳均可引出VEMP,5例2耳均不能引出。总104耳中,94耳阳性,10耳阴性,阳性率90%。统计阳性耳各参数:p1潜伏期(15.97±3.22)ms、n2潜伏期(24.41±2.46)ms、p1n2间期(8.41±2.06)ms,幅值(33.27±14.37)μV,阈值(93.67±5.20)dB nHL。统计47例正常人同一个体耳内差异的各参数为p1潜伏期(0.97±1.31)ms,n2潜伏期(1.23±1.30)ms,p1n2间期(0.95±1.21)ms,幅值(10.04±11.88)μV,阈值(2.29±2.56)dB nHL。男女各参数比较差异无统计学意义。结论:绝大部分正常人可引出VEMP。VEMP的引出体现该侧耳球囊→前庭下神经→脑干前庭神经核→前庭脊髓通路→颈肌运动神经元这条反射途径的完整性。VEMP可能成为一种检测前庭终器及其传导通路完整性的方法。     

Vestibular evoked myogenic potentials in children after cochlear implantation

Objective

The aim of this study was to report the effect of unilateral cochlear implantation to vestibular system using vestibular evoked myogenic potentials (VEMPs) by air-conduction in a sample of children aged less than 5 years.

Materials

This study consisted of 10 children (6 boys and 4 girls), who underwent cochlear implantation surgery at our clinic, and 8 normal hearing children (5 boys and 3 girls) matched for age. The VEMPs were performed before, 10 days, and 6 months after surgery. Both the implanted and unimplanted ears of each child were evaluated, with the cochlear implant both off and on.

Results

Preoperatively, six (60%) children had abnormal VEMPs responses on both ears. In the postoperative sessions, no child showed any VEMPs response on the implanted side. The VEMPs were not recorded on the unimplanted side either, except for one case. At 6 months, the VEMPs response on the unimplanted side of three children became normal when the cochlear implant was on, and in two children with the device off.

Conclusion

In the postoperative 6-month-period, the disappearance of VEMPs suggests that the saccule of children can be extensively damaged following cochlear implantation. A recovery of VEMPs can take place on the unimplanted side, with the cochlear implant both on and off. Despite this saccular injury, the absence of clinical signs in children could be explained by their ability to effectively compensate for such vestibular deficits.     

Low-frequency distortion product otoacoustic emission test compared to ECoG in diagnosing endolymphatic hydrops

Previous studies assumed that specific audiometric measures like low-frequency biasing were noninvasive and inexpensive techniques for diagnosing endolymphatic hydrops (EH). The aim of this study was to compare the results of low-frequency DPOAE (LF-DPOAE) with those of transtympanic electrocochleography (ECoG) in patients with Menière’s disease (MD). The prospective study included 50 patients, 22 to 72 years old, who were diagnosed with Menière’s disease according to the criteria laid down by the American Academy of Otolaryngology—Head and Neck Surgery (AAO-HNS) in 1995. LF-DPOAE and ECoG were performed on the same day after standard audiometry. Enlarged amplitude of summation potential to action potential ratio was used as the diagnostic criterion for EH. The results were compared to those of LF-DPOAE. In this audiometric examination we used the modulation index (MI) to detect EH if MI < 0.5. ECoG yielded a result in 46 of the 50 patients examined. An enlarged SP/AP ratio was found in 23 patients (50%). The results of 33 patients could be compared, i.e. assessable results in both tests. The two tests yielded the same results in 13 patients and different ones in 20 patients. ROC analysis and Mann–Whitney statistics showed no significant correlation between the two tests. With ECoG as the gold standard for verifying EH, we found that LF-DPOAE is not yet a suitable method for diagnosing EH.     

前庭诱发肌源性电位对眩晕患者的诊断价值

目的通过记录、分析眩晕患者的前庭诱发肌源性电位(VEMP),了解眩晕患者的球囊功能。方法对15例梅尼埃病患者和16例突聋伴眩晕患者行VEMP检查,分析其VEMP的不同表现形式,并将该结果与冷热试验结果比较。结果正常双侧短纯音刺激p13波和n23波出现率为100%,30%梅尼埃病患者、50%突聋伴眩晕患者VEMP不能正常引出,VEMP患侧有3种表现形式：无反应,振幅正常,振幅低。结论VEMP检查有助于客观评价眩晕患者球囊功能。     

Electrophysiological measures of cochlear function in guinea pigs with long-term endolymphatic hydrops

Experimental endolymphatic hydrops was induced in guinea pigs by obliteration of the endolymphtic sac and duct. From 3 to 24 months after this operation, cochlear action potential (AP) audiograms and AP tuning curves were measured. The purpose of this study was to establish parallels, if any, between this supposed animal model of Menière's disease and the auditory symptoms of the disease in man. In some animals, low and middle frequency AP threshold elevations were observed whilst higher frequency regions maintained normal sensitivity. Other animals developed flat or very gradually sloping AP audiograms. These patterns are qualitatively similar to those found clinically in Menière's disease. AP tuning curves measured in frequency regions of threshold elevation indicated a deterioration of cochlear frequency selectivity; psychophysical and electrocochleographic studies demonstrate related changes in Menière's patients. One animal exhibited modifications in AP thresholds and tuning as a result of glycerol administration. These observations improve our confidence in the validity of this animal model for further studies of the pathophysiology of Menière's disease.     

Vestibular evoked myogenic potentials in brainstem stroke

OBJECTIVES/HYPOTHESIS: Despite its widespread application in the posterior fossa tumor, the study of vestibular evoked myogenic potential (VEMP) in cases of posterior fossa stroke remains scarce. The purpose of the study was to establish the role of VEMP in patients with brainstem stroke. STUDY DESIGN: Retrospective study. METHODS: Patients with acute vertigo were admitted and underwent a battery of auditory vestibular tests including caloric and VEMP tests; then they were surveyed by magnetic resonance imaging scan. Seven patients (two men and five women) were demonstrated as having brainstem stroke, including infarction in five patients and hemorrhage in two. RESULTS: Clinical manifestations consisted of dizziness/vertigo in all patients, spontaneous nystagmus in five (71%), and ataxia in three. No patients had experienced conscious change or conventional neurological deficits (eg, long tract signs). Electronystagmography revealed abnormal findings on eye tracking test in 100% of patients, on optokinetic nystagmus test in 71% of the patients, and on caloric testing in 10 ears (71%), including absent ice-water caloric test response in 7 ears and canal paresis in 3 ears. Vestibular evoked myogenic potential testing displayed normal response in 3 ears and abnormal response in 11 ears (79%), including absent vestibular evoked myogenic potentials in 8 ears and delayed vestibular evoked myogenic potentials in 3 ears. When results of both caloric testing and VEMP test were combined, the abnormal rate increased to 93% (13 of 14 patients). CONCLUSIONS: Caloric testing assesses the vestibulo-ocular reflex, which passes upward through the upper brainstem, whereas VEMP testing evaluates the sacculocollic reflex, which travels downward through the lower brainstem. Hence, in evaluating the extension of brainstem stroke, both caloric and VEMP testing should be performed.     

Vestibular evoked myogenic potentials in benign paroxysmal positional vertigo and Meniere’s disease

The objective was to investigate vestibular evoked myogenic potentials (VEMP) in benign paroxysmal positional vertigo (BPPV) and Meniere’s disease, and to determine if this type of testing is valuable for assessing the vestibular system. A prospective controlled clinical study was designed in a tertiary referral center setting. The 62 participants included 17 healthy controls and 45 other subjects selected from patients who presented with the complaint of vertigo (25 diagnosed with BPPV and 20 diagnosed with Meniere’s disease). The main outcome measures of VEMP were recorded in all subjects and findings in each patient group were compared with control findings. The VEMP for the 30 affected ears in the 25 BPPV patients revealed prolonged latencies in eight ears and decreased amplitude in one ear (nine abnormal ears; 30% of total). The recordings for the 20 affected ears in the Meniere’s disease patients revealed four ears with no response, six ears with prolonged latencies (ten abnormal ears; 50% of total). Only two (5.9%) of the 34 control ears had abnormal VEMP. The rate of VEMP abnormalities in the control ears was significantly lower than the corresponding rates in the affected BPPV ears and the affected Meniere’s ears that were studied (P=0.012 and P<0.001, respectively). The results suggest that testing of VEMP is a promising method for diagnosing and following patients with BPPV paroxysmal positional vertigo and Meniere’s disease. Further investigations with this method in other neurotologic pathologies might also be informative.     

Vestibular evoked myogenic potentials in basilar artery migraine

OBJECTIVES/HYPOTHESIS: Because the sacculocollic reflex is a descending pathway passing through the territory of basilar artery, the aim of the study was to investigate whether hypoperfusion affects this pathway by applying vestibular evoked myogenic potential (VEMP) testing in patients with basilar artery migraine. STUDY DESIGN: A prospective study from May 2000 to April 2002. METHODS: Twenty patients were diagnosed as having basilar artery migraine according to the criteria of the International Headache Society and literature. Eight were male and 12 were female patients, and their ages ranged from 9 to 48 years (mean age, 40 y). Each patient underwent a battery of audio-vestibular tests. RESULTS: Electronystagmography disclosed abnormal eye tracking test in six patients (30%), and there were abnormal optokinetic nystagmus test results in nine patients (45%). Caloric test revealed canal paresis in seven patients, directional preponderance in four patients, and normal responses in nine patients (45%). Vestibular evoked myogenic potential testing disclosed absent vestibular evoked myogenic potentials in seven patients and delayed vestibular evoked myogenic potentials in two patients, with one patient showing absent vestibular evoked myogenic potentials on one side and delayed vestibular evoked myogenic potentials on the other side. The remaining 10 patients (50%) had bilateral normal vestibular evoked myogenic potentials. Five patients had preserved both caloric and VEMP test responses, six patients displayed absent caloric and VEMP test responses, and the remaining nine patients had either abnormal caloric test responses or abnormal vestibular evoked myogenic potentials, exhibiting a nonsignificant relationship between caloric test responses and vestibular evoked myogenic potentials. Relief of headache and vertigo was achieved after 3 months of medication. Ten asymptomatic patients with either absent or delayed vestibular evoked myogenic potentials before treatment underwent follow-up VEMP test, and nine patients (90%) displayed normal vestibular evoked myogenic potentials bilaterally. CONCLUSION: Vestibular evoked myogenic potential testing evaluates the sacculocollic reflex, which descends through the lower brainstem. Some patients with basilar artery migraine have absent or delayed vestibular evoked myogenic potentials, presumably because the descending pathway from the saccule through the brainstem to cranial nerve XI is interrupted, which is attributed to hypoperfusion in the territory of the basilar artery. After 3 months of medication, recovery of normal vestibular evoked myogenic potentials in an asymptomatic patient indicates reversible ischemia in the territory of the basilar artery.     

甘油对梅尼埃病患者前庭诱发的肌源性电位的影响

目的通过梅尼埃病患者前庭诱发的肌源性电位(vestibulare voked myogenic potential,VEMP)在甘油试验前后的变化情况,了解本项检查在梅尼埃病诊断中的意义。方法对明确诊断为梅尼埃病的10例患者进行甘油试验,比较甘油试验前后前庭诱发的肌源性电位的变化。甘油试验VEMP观察时间段选择两点,服用甘油前及服用甘油后3小时的振幅变化作为指标。结果8例单侧梅尼埃病,其中5例振幅改善(2例振幅增加,3例振幅从无到有),3例甘油试验后VEMP的振幅变差。2例双侧梅尼埃病,1例甘油试验后VEMP振幅从无到有,1例VEMP振幅改善。结论梅尼埃病患者甘油试验后,VEMP变化有以下三种情况:①从无到有;②引出的振幅降低;③引出的振幅提高。甘油试验纯音听力检查结合VEMP的甘油试验有助于梅尼埃病的诊断。     

Augmentation of vestibular evoked myogenic potentials: an indication for distended saccular hydrops

OBJECTIVE/HYPOTHESIS: Vestibular evoked myogenic potential (VEMP) testing has become a well-established test to explore the sacculo-collic pathways in human. The aim of the present study is to establish a clinical indication for saccular hydrops by VEMP testing. STUDY DESIGN: Prospective study. METHODS: Ten patients (three men and seven women) with Meniere's disease and 10 patients (four men and six women) with sudden deafness were admitted and given pure-tone audiometry and VEMP testing daily. Interaural amplitude difference over the sum of amplitudes of both ears was measured, and when the ratio exceeded 0.36, the test result was coined "augmented VEMP." RESULTS: During admission, three hydropic ears presented with augmented VEMP test results, with increased interaural amplitude difference ratio (mean difference ratio, 0.40+/-0.03). Seven hydropic ears had steady VEMP test results, with a mean interaural amplitude difference ratio of 0.15+/-0.07. Compared with the normal control ears, all had steady VEMP test results, with a mean interaural amplitude difference ratio of 0.14+/-0.11, which is significantly different from the hydropic ears with augmented VEMP test results (P <.05). In another 10 patients with sudden deafness, all had positive steady VEMP test results, with their mean interaural amplitude difference ratio of 0.14+/-0.12, which is similar to that in the control ears. CONCLUSIONS: Augmented VEMP test results are an indication of distended saccular hydrops, whose distended wall is in contact with the footplate. VEMP testing may be beneficial in differentiating the initial stage of Meniere's disease and sudden deafness.     

Vestibular evoked myogenic potentials (VEMP) can detect asymptomatic saccular hydrops

OBJECTIVE: The objective of this study was to explore the useful of vestibular evoked myogenic potential (VEMP) testing for detecting endolymphatic hydrops, especially in the second ear of patients with unilateral Ménière disease (MD). METHODS: This study was performed at a tertiary care academic medical center. Part I consisted of postmortem temporal bone specimens from the temporal bone collection of the Massachusetts Eye & Ear Infirmary; part II consisted of consecutive consenting adult patients (n = 82) with unilateral MD by American Academy of Otolaryngology-Head and Neck Surgery criteria case histories. Outcome measures consisted of VEMP thresholds in patients and histologic saccular endolymphatic hydrops in postmortem temporal bones. RESULTS: Saccular hydrops was observed in the asymptomatic ear in six of 17 (35%) of temporal bones from donors with unilateral MD. Clinic patients with unilateral MD showed elevated mean VEMP thresholds and altered VEMP tuning in their symptomatic ears and, to a lesser degree, in their asymptomatic ears. Specific VEMP frequency and tuning criteria were used to define a "Ménière-like" response. This "Ménière-like" response was seen in 27% of asymptomatic ears of our patients with unilateral MD. CONCLUSIONS: Bilateral involvement is seen in approximately one third of MD cases. Saccular hydrops appears to precede symptoms in bilateral MD. Changes in VEMP threshold and tuning appear to be sensitive to these structural changes in the saccule. If so, then VEMP may be useful as a detector of asymptomatic saccular hydrops and as a predictor of evolving bilateral MD.