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KMID : 0350519950480010247
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Journal of Catholic Medical College
1995 Volume.48 No. 1 p.247 ~ p.255
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Histological Changes of the Tympanic Membrane and the Mucosa of the Middle Ear After Application of 5% Tetracaine and 95% Dimethylsulfoxide in the Guinea Pig
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Abstract
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Topical anesthesia and infiltration block with local anesthetics have been used frequently for minor procedures such as myringotomy and insertion of tympanostomy tube. Topical anesthesia has some advantages ; simple, easy to perform and cost
effective,
but it's effect is not satisfactory and complete. Dimethylsulfoxide was used to-improve the effect of topically applied anesthetics.
The purpose of this study was to investigate morphological effect of tetracaine and dimethyl sulfoxide on the tympanic membrane and the mucosa of the middle ear in the guinea pig by light microscopy.
Forty eight healthy guunea pigs, weighing about 300 g, exhibiting normal external auditory canal and tympanic membrane, were equally divided into two groups. The left external auditory canals of the first group were treated with 5% tetracaine
base
in
95% dimethyl sulfoxide solution for 15 minutes. The left external anditory canals of the cecond group were treated with 95% dimethyl dulfoxide alone. The four left temporal bones of animals in each group were taken on 4 hours, 1st-day, 3rd-day,
7th-day,
14th-day 28th-day after the application of the agents. Normal control groups were observed on the specimens of the contralateral side in the above groups.
The initial change observed was damage of the outer epithelial layers of the tympanic membrane, later also accompanied by changes in the corresponding inner mucosal layer. No perforations were observed macroscopically. The healing process was
characterized by hyperplasia of the connective tissue layers of the tympanic membrane. However, the most prominent feature of this process was the regeneration of the outer and inner epithelium of the tympanic membrane. Tetracaine base in
dimethyl
sulfoxide caused a loss of epithelium of the outer and inner layer on the 3rd day. Regeneration started on the 7th day in the tympanic membranes treated tith tetracaine membranes treated with tetracaine base in dimethyl sulfoxide or dimethyl
sulfoxide
alone. On the 28th day, tympanic membrane was recovered to normal tympanic membrane. We could find minor swelling of the mucosa of the middle ear and attic effusion on the 3rd and 7th day. But marked histological changes were not found on the
mucosa of
the oval window and round window. And the histological changes were similar for two agents tested, although minor diferences in degree were noted between two groups.
As a results of the above observation, it could be concluded that an transient structural changes in the tympanic membrane were obvious when using these clinically potent agents, but it did not leave irreversible structural changes.
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