Mikulec Anthony A, McKenna Michael J, Ramsey Mitchell J, Rosowski John J, Herrmann Barbara S, Rauch Steven D, Curtin Hugh D, Merchant Saumil N
Department of Otology and Laryngology, Harvard Medical School, and the Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114, USA.
Otol Neurotol. 2004 Mar;25(2):121-9. doi: 10.1097/00129492-200403000-00007.
The objective of this study was to describe superior semicircular canal dehiscence (SSCD) presenting as otherwise unexplained conductive hearing loss without vestibular symptoms.
Retrospective.
Tertiary referral center.
The study comprised 8 patients (10 ears), 5 males and 5 females aged 27 to 59 years. All 10 ears had SSCD on high-resolution computed tomography scan of the temporal bone. DIAGNOSTIC TESTS AND RESULTS: All 10 ears had significant conductive hearing loss. The air-bone gaps were largest in the lower frequencies at 250, 500, and 1000 Hz; the mean gaps for these 3 frequencies for the 10 ears were 49, 37, and 35 dB, respectively. Bone-conduction thresholds below 2000 Hz were negative (-5 dB to -15 dB) at one or more frequencies in 8 of the 10 ears. There were no middle ear abnormalities to explain the air-bone gaps in these 10 ears. Computed tomography scan and laboratory testing indicated lack of middle ear pathology; acoustic reflexes were present, vestibular evoked myogenic potentials (VEMPs) were present with abnormally low thresholds, and umbo velocity measured by laser Doppler vibrometry was above mean normal. Middle ear exploration was negative in six ears; of these six, stapedectomy had been performed in three ears and ossiculoplasty in two ears, but the air-bone gap was unchanged postoperatively. The data are consistent with the hypothesis that the SSCD introduced a third mobile window into the inner ear, which in turn produced the conductive hearing loss by 1) shunting air-conducted sound away from the cochlea, thus elevating air-conduction thresholds; and 2) increasing the difference in impedance between the oval and round windows, thus improving thresholds for bone-conducted sound.
SSCD can present with a conductive hearing loss that mimics otosclerosis and could explain some cases of persistent conductive hearing loss after uneventful stapedectomy. Audiometric testing with attention to absolute bone-conduction thresholds, acoustic reflex testing, VEMP testing, laser vibrometry of the umbo, and computed tomograph scanning can help to identify patients with SSCD presenting with conductive hearing loss without vertigo.
本研究的目的是描述表现为原因不明的传导性听力损失且无前庭症状的上半规管裂（SSCD）。
回顾性研究。
三级转诊中心。
本研究包括8例患者（10耳），5例男性和5例女性，年龄在27至59岁之间。颞骨高分辨率计算机断层扫描显示所有10耳均有SSCD。诊断测试及结果：所有10耳均有明显的传导性听力损失。气骨导差在250、500和1000Hz的低频处最大；这10耳在这3个频率的平均气骨导差分别为49dB、37dB和35dB。10耳中有8耳在2000Hz以下的一个或多个频率处骨导阈值为阴性（-5dB至-15dB）。这10耳中没有中耳异常来解释气骨导差。计算机断层扫描和实验室检查表明无中耳病变；存在声反射，前庭诱发肌源性电位（VEMP）存在且阈值异常低，激光多普勒振动测量法测量的鼓膜脐速度高于正常均值。6耳中耳探查结果为阴性；其中6耳中，3耳已行镫骨切除术，2耳已行听骨链成形术，但术后气骨导差未改变。数据与以下假设一致，即SSCD在内耳引入了第三个活动窗，进而通过以下方式导致传导性听力损失：1）将气导声音从耳蜗分流，从而提高气导阈值；2）增加椭圆窗和圆窗之间的阻抗差异，从而改善骨导声音的阈值。
SSCD可表现为类似耳硬化症的传导性听力损失，并可解释一些镫骨切除术后持续性传导性听力损失的病例。关注绝对骨导阈值的听力测试、声反射测试、VEMP测试、鼓膜脐激光振动测量以及计算机断层扫描有助于识别表现为无眩晕的传导性听力损失的SSCD患者。
