Endolymphatic Imaging Of Healthy Subjects Using MRI

Background:Meniere's disease(MD) is an idiopathic inner ear disease which has the manifestations of recurrent rotatory dizziness attack, fluctuating sensory hearing loss, tinnitus and fullness of inner ear. The basic pathology of MD is endolymphatic hydrops. In clinic, pathological examinations can not be done in patients with MD and there is no other examinations to check out endolymphatic hydrops, so the diagnosis of MD mostly relys on typical symptoms and assistance of electrocochleography (EcochG), vestibular evoked myogenic potential (VEMP), glycerol test, vestibular function examination and so on, but without objective imaging diagnosis. In the early stage of MD, it is always lack of typical manifestations, so the diagnosis and antidiastole are very difficult. So it's very helpful to diagnosis endolymphatic hydrops if there is a method to image endolymphatic space of inner ear using MRI. Endolymphatic imaging is an international focus recently. The endolymphatic space of inner ear can be imaged by use of enhancer, and the administrating route has advanced from systemic to local, from invasive to non-invasive. But there is no research of endolymphatic imaging in healthy subjects yet.Objective:To prove the feasibility and security of endolymphatic imaging via non-invasive intratympanic gadopentetic acid perfusion through eustachian tube in healthy subjects.Method:There were 28 healthy adult in this study and they were randomly devided into group A and group B. Under observation of auricular endoscope in acoustic duct, we administrated diluted gadopentetic acid(without dexamethasone) to group A and diluted gadopentetic acid(with dexamethasone) to group B via non-invasive intratympanic gadopentetic acid perfusion through eustachian tube. We performed three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging (3D-FLAIR MRI) and two-dimensional fluid-attenuated inversion recovery magnetic resonance imaging (2D-FLAIR MRI) of inner ear on MR machine (3T) 24 hours later. We performed inner ear MRI twice to subject No.A9 8 hours and 24 hours later. We performed pure-tone audiometric testing, acoustic impedance audiometry, EcochG and VEMP before administration and pure-tone audiometric testing, acoustic impedance audiometry 1-2 weeks and a month later after administration.Results:1. We could see fluid level in mid-ear cavity via auricular endoscope in 9 subjects of group A and 8 of group B when administrating.2. We could see perilymphatic enhancement in 3D-FLAIR and 2D-FLAIR MR images of inner ear in the subjects proposed in result 1. There is no enhancement in scalea media, utricle and sacculus. Subject No.A9 undergone MRI 8 and 24 hours later after administration, we could see that the diffusion of gadopentetic acid is more extensive in the MR images of 24 hours than those of 8 hours. The achievement ratio of this endolymphatic imaging method is 61%. In the early stage of our experiment the achievement ratio of the 18 subjects is 44%, and in the late stage the achievement ratio of the 10 subjects is 90%.3. In the period of administration, there was transient painful sensory in all of the 28 subjects when installing catheter into eustachian tube. Transient rotatory dizziness happened in 6 of the 28 subjects, fullness of ear happened in 19 subjects, tinnitus which sound like flowing water happened in 20 subjects. Cough happened in 1 subject. All of the symptoms disappeared in 5 minutes after administration.4. We followed up 25 subjects in 1-2 weeks, the results of pure-tone audiometric testing and acoustic impedance audiometry of 24 subjects were normal, and had no significant differences to those examined before administration. In subjects B5, we could see the slight hearing loss of air conduction, but the result of acoustic impedance audiometry of was normal.We followed up 24 subjects after a month, the results of pure-tone audiometric testing and acoustic impedance audiometry were normal, and had no significant differences to those examined before administration.Conclusion:Intratympanic gadopentetic acid perfusion through eustachian tube is a safe, efficient, non-invasive administrating method which has less pain and complications. The MR images of inner ear after administration can distinguish perilymphatic and endolymphatic spaces. The gadopentetic acid moved from initial part of basal turn and vestibular to apical turn and semicircular canals. Dexamethasone has little influence to visualization degree of the inner ear in healthy subjects.