Presentation
Progressive sensorineural hearing loss. Work-up for cochlear implantation. There is no other significant chronic medical abnormality.
Patient Data
The osseous vestibular aqueducts are enlarged bilaterally. They measure 1.9 mm on the right and 2.9mm on the left, at their midpoints (normal measurement is up to 1.5 mm).
There is no abnormal regional bone erosion to suggest an endolymphatic tumor.
There is minimal right mastoid tip opacification.
High-resolution CT imaging of the temporal bones is otherwise normal.
There are enlarged endolymphatic ducts and endolymphatic sacs bilaterally. There are no endolymphatic sac tumors bilaterally. There is bilateral mastoid tip opacification consistent with uncomplicated mastoid effusions.
There are no other associated congenital ear anomalies identified, specifically, the cochlear and semi-circular canals appear normal.
Case Discussion
An example of bilateral enlarged vestibular aqueducts on CT imaging for cochlear implant work-up.
MRI greatly increases the confidence of the diagnosis with the identification of bilateral enlarged endolymphatic ducts and sacs as demonstrated.
3D high-resolution and thin-slice T2 gradient-echo acquisition of the temporal bones is an essential sequence for assessment and pre-operative planning for cochlear implantation 2.
Enlarged endolymphatic ducts and sacs may be mistaken for flow-related artefacts and or thrombosis within the regional sigmoid sinuses. Occasionally they have also been reported as arachnoid cysts or arachnoid granulations. A careful analysis of the findings will prevent these misdiagnoses.
Enlarged endolymphatic ducts and sacs can be congenital or acquired 2.
The presence of loose connective and fibrous tissue predominantly in the posterior part of the enlarged duct near the sigmoid sinus, accounts for the low signal intensity that is often seen 2. This differential signal intensity between the anterior and posterior duct and sac is well demonstrated in the T2 gradient echo thin-slice acquisition.
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