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Figure 22b.  (a) Dilated vestibular aqueduct in a patient with bilateral sensorineural hearing loss (worse on the right side). Axial CT scan of the right temporal bone shows a dilated vestibular aqueduct (white arrow). The diameter of the duct is greater than that of the adjacent posterior semicircular canal (black arrow). (b) Axial CT scan obtained in a different patient demonstrates a normal-sized vestibular aqueduct (white arrow). The posterior semicircular canal (black arrow) is shown for comparison.