上鼓室耳小骨骨性固着症とprimary mastoid cystの併発例

Epitympanic Ossicular Fixation with Primary Mastoid Cyst

I．緒言

　手術の既往がなく乳突洞に嚢胞が発生するpri—mary mastoid cystは比較的稀な疾患とされ，成因としては慢性炎症，外傷，先天異常などが考えられている。症状はさまざまであるが，特徴的な臨床像に乏しく，巨大な嚢胞を形成するまで症状が出現せず，X線撮影により発見される^1）ことも多く，また多くの報告では乳突蜂巣の骨破壊を伴うX線透過像が認められている。

　一方つち骨・きぬた骨と上鼓室との固着は，つち骨癒着症が代表的なものとして知られており，鼓室硬化症，中耳癒着症，耳硬化症の部分症状，先天性奇形，慢性炎症刺激による靱帯の骨化などが原因^2）と考えられている。

A 50-year-old man suffered from progressive left hearing loss and tinnitus for the past ten years. The tympanic membrane showed a mild retraction in the pars flaccida and the malleus was extremely immobile. An audiogram showed a severe com-bined hearing loss with a moderate increase of a bone conduction. Computed tomography revealed a isodensity mass in the mastoid and suggested that the malleus head and incus body were con-nected with the scutum.

He underwent exploratory mastoidectomy. The mass in the mastoid was a cholesterol cyst with osseous obstruction of the aditus and bony fixation of the malleus head and incus body to the lateral wall of the epitympanum was present. Posterior tympanotomy was done and bony fixation was removed. Post-operatively, the hearing was im-proved and tinnitus ceased.