Effect of an enlarged endolymphatic duct on bone conduction threshold.
An enlarged endolymphatic duct and sac (EDS) that makes contact with the cerebrospinal fluid–dural interface plays an important role in the pathway of bone conduction and enhances bone conduction at lower frequencies. Objectives. We investigated whether the bone conduction threshold was improved when the EDS was enlarged. Subjects and methods. Twenty-three patients (46 ears) with large vestibular aqueducts underwent standard pure tone audiometry (PTA) and magnetic resonance imaging (MRI) to investigate the relation between the diameter of the endolymphatic duct (ED) and the air or bone conduction threshold. We also investigated the relation between the volume of the EDS and the air or bone conduction threshold. Results. All ears had a mixed type hearing loss. The air–bone gaps were significantly larger at 250 and 500 Hz than at higher frequencies. The bone conduction thresholds were significantly lower at 250 Hz and 1000 Hz when the diameter of the ED was large, whereas there was no relation between the diameter of the ED and the air conduction threshold. In addition, there was no correlation between the volume of the EDS and air or bone conduction thresholds.
Sato
Eisuke
E
Department of Otorhinolaryngology, Nagoya University School of Medicine, Nagoya, Japan.  satoe@ccf.org
Sugiura
Makoto
M
Naganawa
Shinji
S
Yoshino
Takahiko
T
Mizuno
Terukazu
T
Otake
Hironao
H
Ishida
Ieda Maria
IM
Nakashima
Tsutomu
T