| Objective Examination animal models of endolymphatic hydrops by electrocochleogram, auditory brainstem response and histologic morphometry was undertaken to investigate the correlation between morphologic and functional changes in cochleas, and to provide animal experiment data for verification and rectification of internal ear finite element model.Methods 1. Thirty albino guinea pigs were randomly divided into three groups. One group is control group (n=10), the animals were sham operated. The other group is model group (n=20), and they were operated on the right ears to result in endolymphatic hydrops with the method of slight destruction of endolymphatic sac and duct from extradural posterior cranial fossa approach. The left ears remained as internal histologic controls. The model group is randomly divided into model-4-weeks group (n=10) and model-8-weeks group (n=10).2. Electrocochleogram was tested with preoperative animals, control group, model-4-weeks group and model-8-weeks group. Hearing was assessed from 2 kHz to 32 kHz by auditory brainstem response.3. Histologic morphometry after 5 animals in every group were killed was used to quantify turn-specific hydrops by testing scala media area ratio. Statistical analysis was undertaken to investigate the correlation between scala media area ratio and hearing loss.4.5 animals in every group were killed was tested by scanning electron microscope to quantify turn-specific stereocilia of cochlea hair cells. Statistical analysis was undertaken to investigate the correlation between cochlea hair cells damage and hearing loss.Results 1.The SP/AP ratio of electrocochleogram in control group, model-4-weeks group and model-8-weeks group were 0.0668±0.06,0.3273±0.14, 0.4256±0.14 respectively. There were significant differences between model groups and control group (P<0.05)2. The results of hearing threshold of ABR revealed that the operated ears of model groups were higher than the preoperative results in frequency of 2 kHz and 4 kHz. There were significant differences respectively in this two frequencies (P<0.05), but there were no significant differences in other frequencies.3. The results of turn-specific SMA ratio revealed that the model groups were more than control group. There were significant differences respectively (P<0.05) Hearing loss in the frequencies of 2 kHz and 4 kHz correlated with turn-specific hydrops. However, turn-specific hydrops did not reliably correlate with the magnitude of hearing loss at anatomically appropriate frequency ranges. The results of maximum SMA ratio correlated with SP/AP ratio of electrocochleogram.4. The results of quantify turn-specific stereocilia of cochlea hair cells revealed that the model groups were less than control group in apical and subapical turn. There were significant differences respectively (P<0.05). The quantity of stereocilia of cochlea hair cells in apical turn correlated with hearing loss in 2 kHz, and the quantity of stereocilia of cochlea hair cells in subapical turn correlated with hearing loss in 4 kHz.Conclusions 1.The animal models of endolymphatic hydrops can be induced by surgical obstruction of the endolymphatic sac and duct, and we found that there are low-tone hearing loss in the the animal models.2.The SP/AP ratio of electrocochleogram can reveal early endolymphatic hydrops.3.There are turn-specific hydrops in the the animal model especially in subapical and suprabasilar turn, and the damage of cochlea hair cells occurs in apical and subapical turn. This is correlated with low-tone hearing loss. |
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