伝音性難聴の鑑別診断—耳小骨奇形および外傷性伝音難聴について

Differential Diagnosis of Conductive Deafness with Intact Tympanic Membrane

I．はじめに

　鼓膜正常な伝音性難聴において術前に中耳内の病態を正確に把握することは，手術方法の選択，術後成績の見通しに関して重要な意義を持つ。一般に鼓膜正常耳の中耳病態の診断は近年computedtomographyが耳科学領域に盛んに用いられるようになったとはいえ，依然として聴覚学的諸検査に負うところは大きい。

　なかんずくstatic impedance，ティンパノメトリー，耳小骨筋反射の有用性はすでに多数の研究者によって証明され^1〜7），臨床的に広く応用されている。

　今回われわれは自験例18例を対象に当科で最もルーチンに行われている純音聴力検査，ティンパノメトリー，耳小骨筋反射の術前検査成績に基づき，これら3検査併用での診断率を求め若干の考察を加えたので報告する。

　The efficacy of tympanometry, acoustic reflex testing and pure tone audiometry in assessment of conductive deafness with intact tympanic membrane in 18 patients was evaluated retrospectively. The preoperative diagnosis was compared with the postoperative diagnosis, and usefulness of the tests was evaluated. There were 15 cases of congenital and 3 cases of posttraumatic deafness.

　Conductive hearing loss curves on puretone audiogram were classified into stiffness type, middle ear blockage type and the others. Tympanograms were classified according to jerger's classification into Type A, As, An and the others. Acoustic reflex tests were compared with each other, and divided into positive, low and negative reflex types.

　Preoperative diagnosis of fixation or discontinuity of the ossicular chain was compared with the postoperative diagnosis. From the results obtained the following conclusions were obtained.

　1. An air-bone gap of over 35 dB at 4,000 Hz is suggestive of ossicular discontinuity. Less than 35 dB A-B gap suggests ossicular fixation in congenital conductive deafness.

　2. Tympanometry is also useful for the differentiations of fixation and discontinuity of the ossicular chain.

　3. Comparison of ipsilateral and contralateral acoustic reflexes of the affected ear is some-times useful for determining the site of discontinuity of the ossicular chain.