Atlas of HeadNeck and Spine Normal Imaging Variants by unknow

Author:unknow
Language: eng
Format: epub
ISBN: 9783319954417
Publisher: Springer International Publishing

5.4.1 Vestibular Aqueduct: Normal Size and Appearance

The vestibular aqueduct (VA) connects the endolymphatic sac to the vestibule (serving as a conduit between the inner ear and cranial vault and carrying endolymph); the endolymphatic duct runs within the VA. Regarding the size of the VA, there are several methods of measuring it. A smaller than average VA is considered a normal variant, but an enlarged VA (EVA) is usually pathologic. EVA is one of the most common abnormalities identified in children with sensorineural hearing loss. This is particularly true in those with non–syndromic hearing loss, in whom up to 32% are found to have EVA. When present, EVA is usually bilateral, occurring in 55–94% of affected children, but it can be unilateral as well. While the type of hearing loss is typically sensorineural, there may be a conductive component, potentially due to the “third window” effect of the EVA. The relationship of the degree of the VA enlargement to the severity of hearing loss has been controversial, with some authors reporting a correlation, while others report no association. A 2018 study by Song et al. found hearing loss in 90.2% of EVA ears; of those ears, purely sensorineural hearing loss was found in 92%, with mixed hearing loss in 4.8%, and conductive hearing loss in 2.4%; dizziness was found in 63.6%.

An accepted method of VA measurement is to measure the AP diameter of the aqueduct at its midportion, where quantitatively it should measure less than 1.5 mm, and qualitatively it should be smaller than the adjacent limb of the posterior semicircular canal. An enlarged vestibular aqueduct may be an isolated finding but is frequently seen with Incomplete Partition type 2 and Pendred syndrome. A small VA is typically not present (and is more commonly related to suboptimal slice selection plane), but if present may be associated with Ménière disease, which is typically a clinical diagnosis. However, the exact cause and specific HRMRI diagnostic criteria of Ménière are still being debated. Hence, in summary, it is normal to have a small VA in patients without Ménière disease, but there is a maximum size threshold (1.5–2 mm) that raises the question of EVA syndrome (Figs. 5.17 and 5.18).

Fig. 5.17Comparison cases: Normal versus abnormal vestibular aqueduct sizes in two different patients with unilateral and bilateral vestibular aqueduct enlargement. Top row: In a 6-month-old female with a failed newborn hearing screen of the right ear, axial HRCT shows a normal left vestibular aqueduct (diameter less than 1 mm, arrows, right) and an enlarged right vestibular aqueduct (diameter 2.6 mm, dashed arrow, left). Note that the abnormal right aqueduct (dashed arrow, left) is larger than the diameter of the adjacent crus of the posterior semicircular canal (dotted arrow, left), while the normal left vestibular aqueduct (arrows, right) is smaller than the adjacent posterior semicircular canal (black arrow, right) Bottom row: In a 51-year-old female with bilateral hearing loss since childhood, there are enlarged vestibular aqueducts bilaterally on axial HRCT, which are 2.9 mm on the right side (bracket, left image) and 2.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.