Medical Central Resource
Bilateral Large Vestibular Aqueduct Syndrome
David White
4/10/97
Presentation
13 year old female with sensorineural hearing loss.
Imaging Technique
CT
MRI
Imaging Findings
CT: There is enlargement of the bilateral vestibular aqueducts (5 mm's)
MR: There is enlargement of the bilateral endolymphatic ducts and sacs.
Diagnosis
Bilateral Large Vestibular Aqueduct Syndrome
Discussion
Because of its high spatial resolution and contrast, CT has been the mainstay of imaging of the inner ear. FSE pulse sequences, with inherent decreased magnetic susceptibility signal loss, are capable of producing excellent quality high resolution T2-weighted images.
The normal endolymphatic duct (ELD) origionates from the anteromedial wall of the vestibule and courses posterolaterally in the bony vestibular aqueduct to merge with the endolymphatic sac (ELS), still in the bony canal. The ELS then emerges from the canal and is positioned between the leaves of the dura overlying the posterior temporal bone. The function of the ELD and ELS are not well known, however they are felt to be responsible for regulating endolymph pressure within the membranous labyrinth.
The large vestibular aqueduct syndrome is thought to be a result of abnormal embryologic development of the ELD and ELS. Hearing is typically present at birth, followed by a stepwise pattern of hearing loss, which may not begin until the teenage years. Onset of hearing loss often follows trauma or other activity that increases CSF pressure. This syndrome is more common in boys and is perhaps the most commonly overlooked cause of hearing loss in children.
Imaging findings:
- CT: Enlargement of the vestibular aqueduct, as described by Dahlen, et. al. and Valvassori, is diagnosed when the aqueduct measures >1.5mm at its midpoint between the common crus and the external aperture. Associated inner ear anomalies, such as enlargement of the upper vestibule, are not uncommon.
- MR: In up to 25% of normal patients, the endolymphatic duct and sac may not be visualized. When visualized, the duct should measure <1.5mm, in transverse diameter.
Submitted by: David K. White,Capt,USAF,MC,Wilford Hall Medical Center
Reviewed by: Richard Dahlen,Maj,USAF,MC,Wilford Hall Medical Center
References
- Dahlen, et.al., Overlapping Thin-Sedtion Fast Spin-Echo MR of the Large Vestibular Aqueduct Sysndrome. AJNR Am J Neuroradiol 18:67-75, January 1997.
- Valvassori GE. The large vestibular aqueduct and associated anomalies of the inner ear. Otolaryngol C/in North Am 1983;16:95-101.
- Imaging of the Temporal Bone, 2nd Ed.Schwartz and Harnsberger Thieme, 1992. pp.199, 208-209.
- Handbook of Head and Neck Imaging, 2nd Ed. H. Ric Harnsberger Mosby, 1995. p.451.
